From: Nhat Pham nphamcs@gmail.com

mainline inclusion from mainline-v6.8-rc1 commit 0a97c01cd20bb96359d8c9dedad92a061ed34e0b category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I8ZUJQ CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...

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Patch series "workload-specific and memory pressure-driven zswap writeback", v8.

There are currently several issues with zswap writeback:

1. There is only a single global LRU for zswap, making it impossible to perform worload-specific shrinking - an memcg under memory pressure cannot determine which pages in the pool it owns, and often ends up writing pages from other memcgs. This issue has been previously observed in practice and mitigated by simply disabling memcg-initiated shrinking:

https://lore.kernel.org/all/20230530232435.3097106-1-nphamcs@gmail.com/T/#u

But this solution leaves a lot to be desired, as we still do not have an avenue for an memcg to free up its own memory locked up in the zswap pool.

2. We only shrink the zswap pool when the user-defined limit is hit. This means that if we set the limit too high, cold data that are unlikely to be used again will reside in the pool, wasting precious memory. It is hard to predict how much zswap space will be needed ahead of time, as this depends on the workload (specifically, on factors such as memory access patterns and compressibility of the memory pages).

This patch series solves these issues by separating the global zswap LRU into per-memcg and per-NUMA LRUs, and performs workload-specific (i.e memcg- and NUMA-aware) zswap writeback under memory pressure. The new shrinker does not have any parameter that must be tuned by the user, and can be opted in or out on a per-memcg basis.

As a proof of concept, we ran the following synthetic benchmark: build the linux kernel in a memory-limited cgroup, and allocate some cold data in tmpfs to see if the shrinker could write them out and improved the overall performance. Depending on the amount of cold data generated, we observe from 14% to 35% reduction in kernel CPU time used in the kernel builds.

This patch (of 6):

The interface of list_lru is based on the assumption that the list node and the data it represents belong to the same allocated on the correct node/memcg. While this assumption is valid for existing slab objects LRU such as dentries and inodes, it is undocumented, and rather inflexible for certain potential list_lru users (such as the upcoming zswap shrinker and the THP shrinker). It has caused us a lot of issues during our development.

This patch changes list_lru interface so that the caller must explicitly specify numa node and memcg when adding and removing objects. The old list_lru_add() and list_lru_del() are renamed to list_lru_add_obj() and list_lru_del_obj(), respectively.

It also extends the list_lru API with a new function, list_lru_putback, which undoes a previous list_lru_isolate call. Unlike list_lru_add, it does not increment the LRU node count (as list_lru_isolate does not decrement the node count). list_lru_putback also allows for explicit memcg and NUMA node selection.

Link: https://lkml.kernel.org/r/20231130194023.4102148-1-nphamcs@gmail.com Link: https://lkml.kernel.org/r/20231130194023.4102148-2-nphamcs@gmail.com Signed-off-by: Nhat Pham nphamcs@gmail.com Suggested-by: Johannes Weiner hannes@cmpxchg.org Acked-by: Johannes Weiner hannes@cmpxchg.org Tested-by: Bagas Sanjaya bagasdotme@gmail.com Cc: Chris Li chrisl@kernel.org Cc: Dan Streetman ddstreet@ieee.org Cc: Domenico Cerasuolo cerasuolodomenico@gmail.com Cc: Michal Hocko mhocko@kernel.org Cc: Muchun Song muchun.song@linux.dev Cc: Roman Gushchin roman.gushchin@linux.dev Cc: Seth Jennings sjenning@redhat.com Cc: Shakeel Butt shakeelb@google.com Cc: Shuah Khan shuah@kernel.org Cc: Vitaly Wool vitaly.wool@konsulko.com Cc: Yosry Ahmed yosryahmed@google.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Ma Wupeng mawupeng1@huawei.com --- drivers/android/binder_alloc.c | 7 ++--- fs/dcache.c | 8 +++-- fs/gfs2/quota.c | 6 ++-- fs/inode.c | 4 +-- fs/nfs/nfs42xattr.c | 8 ++--- fs/nfsd/filecache.c | 4 +-- fs/xfs/xfs_buf.c | 6 ++-- fs/xfs/xfs_dquot.c | 2 +- fs/xfs/xfs_qm.c | 2 +- include/linux/list_lru.h | 56 +++++++++++++++++++++++++++++++--- mm/list_lru.c | 48 ++++++++++++++++++++++++----- mm/workingset.c | 4 +-- 12 files changed, 118 insertions(+), 37 deletions(-)

diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c index e3db8297095a..07bf2ec0cff9 100644 --- a/drivers/android/binder_alloc.c +++ b/drivers/android/binder_alloc.c @@ -234,7 +234,7 @@ static int binder_update_page_range(struct binder_alloc *alloc, int allocate, if (page->page_ptr) { trace_binder_alloc_lru_start(alloc, index);

- on_lru = list_lru_del(&binder_alloc_lru, &page->lru); + on_lru = list_lru_del_obj(&binder_alloc_lru, &page->lru); WARN_ON(!on_lru);

trace_binder_alloc_lru_end(alloc, index); @@ -285,7 +285,7 @@ static int binder_update_page_range(struct binder_alloc *alloc, int allocate,

trace_binder_free_lru_start(alloc, index);

- ret = list_lru_add(&binder_alloc_lru, &page->lru); + ret = list_lru_add_obj(&binder_alloc_lru, &page->lru); WARN_ON(!ret);

trace_binder_free_lru_end(alloc, index); @@ -848,7 +848,7 @@ void binder_alloc_deferred_release(struct binder_alloc *alloc) if (!alloc->pages[i].page_ptr) continue;

- on_lru = list_lru_del(&binder_alloc_lru, + on_lru = list_lru_del_obj(&binder_alloc_lru, &alloc->pages[i].lru); page_addr = alloc->buffer + i * PAGE_SIZE; binder_alloc_debug(BINDER_DEBUG_BUFFER_ALLOC, @@ -1281,4 +1281,3 @@ int binder_alloc_copy_from_buffer(struct binder_alloc *alloc, return binder_alloc_do_buffer_copy(alloc, false, buffer, buffer_offset, dest, bytes); } - diff --git a/fs/dcache.c b/fs/dcache.c index c27aa8ff78f4..0f8c85f0fc4f 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -437,7 +437,8 @@ static void d_lru_add(struct dentry *dentry) this_cpu_inc(nr_dentry_unused); if (d_is_negative(dentry)) this_cpu_inc(nr_dentry_negative); - WARN_ON_ONCE(!list_lru_add(&dentry->d_sb->s_dentry_lru, &dentry->d_lru)); + WARN_ON_ONCE(!list_lru_add_obj( + &dentry->d_sb->s_dentry_lru, &dentry->d_lru)); }

static void d_lru_del(struct dentry *dentry) @@ -447,7 +448,8 @@ static void d_lru_del(struct dentry *dentry) this_cpu_dec(nr_dentry_unused); if (d_is_negative(dentry)) this_cpu_dec(nr_dentry_negative); - WARN_ON_ONCE(!list_lru_del(&dentry->d_sb->s_dentry_lru, &dentry->d_lru)); + WARN_ON_ONCE(!list_lru_del_obj( + &dentry->d_sb->s_dentry_lru, &dentry->d_lru)); }

static void d_shrink_del(struct dentry *dentry) @@ -1278,7 +1280,7 @@ static enum lru_status dentry_lru_isolate(struct list_head *item, * * This is guaranteed by the fact that all LRU management * functions are intermediated by the LRU API calls like - * list_lru_add and list_lru_del. List movement in this file + * list_lru_add_obj and list_lru_del_obj. List movement in this file * only ever occur through this functions or through callbacks * like this one, that are called from the LRU API. * diff --git a/fs/gfs2/quota.c b/fs/gfs2/quota.c index 41d0232532a0..10b990f1dfda 100644 --- a/fs/gfs2/quota.c +++ b/fs/gfs2/quota.c @@ -258,7 +258,7 @@ static struct gfs2_quota_data *gfs2_qd_search_bucket(unsigned int hash, if (qd->qd_sbd != sdp) continue; if (lockref_get_not_dead(&qd->qd_lockref)) { - list_lru_del(&gfs2_qd_lru, &qd->qd_lru); + list_lru_del_obj(&gfs2_qd_lru, &qd->qd_lru); return qd; } } @@ -331,7 +331,7 @@ static void qd_put(struct gfs2_quota_data *qd) }

qd->qd_lockref.count = 0; - list_lru_add(&gfs2_qd_lru, &qd->qd_lru); + list_lru_add_obj(&gfs2_qd_lru, &qd->qd_lru); spin_unlock(&qd->qd_lockref.lock); }

@@ -1505,7 +1505,7 @@ void gfs2_quota_cleanup(struct gfs2_sbd *sdp) lockref_mark_dead(&qd->qd_lockref); spin_unlock(&qd->qd_lockref.lock);

- list_lru_del(&gfs2_qd_lru, &qd->qd_lru); + list_lru_del_obj(&gfs2_qd_lru, &qd->qd_lru); list_add(&qd->qd_lru, &dispose); } spin_unlock(&qd_lock); diff --git a/fs/inode.c b/fs/inode.c index ae1a6410b53d..1eb944b8f100 100644 --- a/fs/inode.c +++ b/fs/inode.c @@ -464,7 +464,7 @@ static void __inode_add_lru(struct inode *inode, bool rotate) if (!mapping_shrinkable(&inode->i_data)) return;

- if (list_lru_add(&inode->i_sb->s_inode_lru, &inode->i_lru)) + if (list_lru_add_obj(&inode->i_sb->s_inode_lru, &inode->i_lru)) this_cpu_inc(nr_unused); else if (rotate) inode->i_state |= I_REFERENCED; @@ -482,7 +482,7 @@ void inode_add_lru(struct inode *inode)

static void inode_lru_list_del(struct inode *inode) { - if (list_lru_del(&inode->i_sb->s_inode_lru, &inode->i_lru)) + if (list_lru_del_obj(&inode->i_sb->s_inode_lru, &inode->i_lru)) this_cpu_dec(nr_unused); }

diff --git a/fs/nfs/nfs42xattr.c b/fs/nfs/nfs42xattr.c index 911f634ba3da..c3744b15579c 100644 --- a/fs/nfs/nfs42xattr.c +++ b/fs/nfs/nfs42xattr.c @@ -132,7 +132,7 @@ nfs4_xattr_entry_lru_add(struct nfs4_xattr_entry *entry) lru = (entry->flags & NFS4_XATTR_ENTRY_EXTVAL) ? &nfs4_xattr_large_entry_lru : &nfs4_xattr_entry_lru;

- return list_lru_add(lru, &entry->lru); + return list_lru_add_obj(lru, &entry->lru); }

static bool @@ -143,7 +143,7 @@ nfs4_xattr_entry_lru_del(struct nfs4_xattr_entry *entry) lru = (entry->flags & NFS4_XATTR_ENTRY_EXTVAL) ? &nfs4_xattr_large_entry_lru : &nfs4_xattr_entry_lru;

- return list_lru_del(lru, &entry->lru); + return list_lru_del_obj(lru, &entry->lru); }

/* @@ -349,7 +349,7 @@ nfs4_xattr_cache_unlink(struct inode *inode)

oldcache = nfsi->xattr_cache; if (oldcache != NULL) { - list_lru_del(&nfs4_xattr_cache_lru, &oldcache->lru); + list_lru_del_obj(&nfs4_xattr_cache_lru, &oldcache->lru); oldcache->inode = NULL; } nfsi->xattr_cache = NULL; @@ -474,7 +474,7 @@ nfs4_xattr_get_cache(struct inode *inode, int add) kref_get(&cache->ref); nfsi->xattr_cache = cache; cache->inode = inode; - list_lru_add(&nfs4_xattr_cache_lru, &cache->lru); + list_lru_add_obj(&nfs4_xattr_cache_lru, &cache->lru); }

spin_unlock(&inode->i_lock); diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c index 07bf219f9ae4..77f98a477bf0 100644 --- a/fs/nfsd/filecache.c +++ b/fs/nfsd/filecache.c @@ -322,7 +322,7 @@ nfsd_file_check_writeback(struct nfsd_file *nf) static bool nfsd_file_lru_add(struct nfsd_file *nf) { set_bit(NFSD_FILE_REFERENCED, &nf->nf_flags); - if (list_lru_add(&nfsd_file_lru, &nf->nf_lru)) { + if (list_lru_add_obj(&nfsd_file_lru, &nf->nf_lru)) { trace_nfsd_file_lru_add(nf); return true; } @@ -331,7 +331,7 @@ static bool nfsd_file_lru_add(struct nfsd_file *nf)

static bool nfsd_file_lru_remove(struct nfsd_file *nf) { - if (list_lru_del(&nfsd_file_lru, &nf->nf_lru)) { + if (list_lru_del_obj(&nfsd_file_lru, &nf->nf_lru)) { trace_nfsd_file_lru_del(nf); return true; } diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c index 4f175540dd22..187f33d2a282 100644 --- a/fs/xfs/xfs_buf.c +++ b/fs/xfs/xfs_buf.c @@ -169,7 +169,7 @@ xfs_buf_stale(

atomic_set(&bp->b_lru_ref, 0); if (!(bp->b_state & XFS_BSTATE_DISPOSE) && - (list_lru_del(&bp->b_target->bt_lru, &bp->b_lru))) + (list_lru_del_obj(&bp->b_target->bt_lru, &bp->b_lru))) atomic_dec(&bp->b_hold);

ASSERT(atomic_read(&bp->b_hold) >= 1); @@ -1052,7 +1052,7 @@ xfs_buf_rele( * buffer for the LRU and clear the (now stale) dispose list * state flag */ - if (list_lru_add(&bp->b_target->bt_lru, &bp->b_lru)) { + if (list_lru_add_obj(&bp->b_target->bt_lru, &bp->b_lru)) { bp->b_state &= ~XFS_BSTATE_DISPOSE; atomic_inc(&bp->b_hold); } @@ -1065,7 +1065,7 @@ xfs_buf_rele( * was on was the disposal list */ if (!(bp->b_state & XFS_BSTATE_DISPOSE)) { - list_lru_del(&bp->b_target->bt_lru, &bp->b_lru); + list_lru_del_obj(&bp->b_target->bt_lru, &bp->b_lru); } else { ASSERT(list_empty(&bp->b_lru)); } diff --git a/fs/xfs/xfs_dquot.c b/fs/xfs/xfs_dquot.c index ac6ba646624d..49f619f5aa96 100644 --- a/fs/xfs/xfs_dquot.c +++ b/fs/xfs/xfs_dquot.c @@ -1064,7 +1064,7 @@ xfs_qm_dqput( struct xfs_quotainfo *qi = dqp->q_mount->m_quotainfo; trace_xfs_dqput_free(dqp);

- if (list_lru_add(&qi->qi_lru, &dqp->q_lru)) + if (list_lru_add_obj(&qi->qi_lru, &dqp->q_lru)) XFS_STATS_INC(dqp->q_mount, xs_qm_dquot_unused); } xfs_dqunlock(dqp); diff --git a/fs/xfs/xfs_qm.c b/fs/xfs/xfs_qm.c index 086e78a6143a..5ef080c3c734 100644 --- a/fs/xfs/xfs_qm.c +++ b/fs/xfs/xfs_qm.c @@ -171,7 +171,7 @@ xfs_qm_dqpurge( * hits zero, so it really should be on the freelist here. */ ASSERT(!list_empty(&dqp->q_lru)); - list_lru_del(&qi->qi_lru, &dqp->q_lru); + list_lru_del_obj(&qi->qi_lru, &dqp->q_lru); XFS_STATS_DEC(dqp->q_mount, xs_qm_dquot_unused);

xfs_qm_dqdestroy(dqp); diff --git a/include/linux/list_lru.h b/include/linux/list_lru.h index b35968ee9fb5..d041355ec835 100644 --- a/include/linux/list_lru.h +++ b/include/linux/list_lru.h @@ -75,6 +75,8 @@ void memcg_reparent_list_lrus(struct mem_cgroup *memcg, struct mem_cgroup *paren * list_lru_add: add an element to the lru list's tail * @list_lru: the lru pointer * @item: the item to be added. + * @nid: the node id of the sublist to add the item to. + * @memcg: the cgroup of the sublist to add the item to. * * If the element is already part of a list, this function returns doing * nothing. Therefore the caller does not need to keep state about whether or @@ -87,12 +89,28 @@ void memcg_reparent_list_lrus(struct mem_cgroup *memcg, struct mem_cgroup *paren * * Return value: true if the list was updated, false otherwise */ -bool list_lru_add(struct list_lru *lru, struct list_head *item); +bool list_lru_add(struct list_lru *lru, struct list_head *item, int nid, + struct mem_cgroup *memcg);

/** - * list_lru_del: delete an element to the lru list - * @list_lru: the lru pointer + * list_lru_add_obj: add an element to the lru list's tail + * @lru: the lru pointer + * @item: the item to be added. + * + * This function is similar to list_lru_add(), but the NUMA node and the + * memcg of the sublist is determined by @item list_head. This assumption is + * valid for slab objects LRU such as dentries, inodes, etc. + * + * Return value: true if the list was updated, false otherwise + */ +bool list_lru_add_obj(struct list_lru *lru, struct list_head *item); + +/** + * list_lru_del: delete an element from the lru list + * @lru: the lru pointer * @item: the item to be deleted. + * @nid: the node id of the sublist to delete the item from. + * @memcg: the cgroup of the sublist to delete the item from. * * This function works analogously as list_lru_add in terms of list * manipulation. The comments about an element already pertaining to @@ -100,7 +118,21 @@ bool list_lru_add(struct list_lru *lru, struct list_head *item); * * Return value: true if the list was updated, false otherwise */ -bool list_lru_del(struct list_lru *lru, struct list_head *item); +bool list_lru_del(struct list_lru *lru, struct list_head *item, int nid, + struct mem_cgroup *memcg); + +/** + * list_lru_del_obj: delete an element from the lru list + * @lru: the lru pointer + * @item: the item to be deleted. + * + * This function is similar to list_lru_del(), but the NUMA node and the + * memcg of the sublist is determined by @item list_head. This assumption is + * valid for slab objects LRU such as dentries, inodes, etc. + * + * Return value: true if the list was updated, false otherwise. + */ +bool list_lru_del_obj(struct list_lru *lru, struct list_head *item);

/** * list_lru_count_one: return the number of objects currently held by @lru @@ -136,6 +168,22 @@ static inline unsigned long list_lru_count(struct list_lru *lru) void list_lru_isolate(struct list_lru_one *list, struct list_head *item); void list_lru_isolate_move(struct list_lru_one *list, struct list_head *item, struct list_head *head); +/** + * list_lru_putback: undo list_lru_isolate + * @lru: the lru pointer. + * @item: the item to put back. + * @nid: the node id of the sublist to put the item back to. + * @memcg: the cgroup of the sublist to put the item back to. + * + * Put back an isolated item into its original LRU. Note that unlike + * list_lru_add, this does not increment the node LRU count (as + * list_lru_isolate does not originally decrement this count). + * + * Since we might have dropped the LRU lock in between, recompute list_lru_one + * from the node's id and memcg. + */ +void list_lru_putback(struct list_lru *lru, struct list_head *item, int nid, + struct mem_cgroup *memcg);

typedef enum lru_status (*list_lru_walk_cb)(struct list_head *item, struct list_lru_one *list, spinlock_t *lock, void *cb_arg); diff --git a/mm/list_lru.c b/mm/list_lru.c index a05e5bef3b40..fcca67ac26ec 100644 --- a/mm/list_lru.c +++ b/mm/list_lru.c @@ -116,21 +116,19 @@ list_lru_from_kmem(struct list_lru *lru, int nid, void *ptr, } #endif /* CONFIG_MEMCG_KMEM */

-bool list_lru_add(struct list_lru *lru, struct list_head *item) +bool list_lru_add(struct list_lru *lru, struct list_head *item, int nid, + struct mem_cgroup *memcg) { - int nid = page_to_nid(virt_to_page(item)); struct list_lru_node *nlru = &lru->node[nid]; - struct mem_cgroup *memcg; struct list_lru_one *l;

spin_lock(&nlru->lock); if (list_empty(item)) { - l = list_lru_from_kmem(lru, nid, item, &memcg); + l = list_lru_from_memcg_idx(lru, nid, memcg_kmem_id(memcg)); list_add_tail(item, &l->list); /* Set shrinker bit if the first element was added */ if (!l->nr_items++) - set_shrinker_bit(memcg, nid, - lru_shrinker_id(lru)); + set_shrinker_bit(memcg, nid, lru_shrinker_id(lru)); nlru->nr_items++; spin_unlock(&nlru->lock); return true; @@ -140,15 +138,25 @@ bool list_lru_add(struct list_lru *lru, struct list_head *item) } EXPORT_SYMBOL_GPL(list_lru_add);

-bool list_lru_del(struct list_lru *lru, struct list_head *item) +bool list_lru_add_obj(struct list_lru *lru, struct list_head *item) { int nid = page_to_nid(virt_to_page(item)); + struct mem_cgroup *memcg = list_lru_memcg_aware(lru) ? + mem_cgroup_from_slab_obj(item) : NULL; + + return list_lru_add(lru, item, nid, memcg); +} +EXPORT_SYMBOL_GPL(list_lru_add_obj); + +bool list_lru_del(struct list_lru *lru, struct list_head *item, int nid, + struct mem_cgroup *memcg) +{ struct list_lru_node *nlru = &lru->node[nid]; struct list_lru_one *l;

spin_lock(&nlru->lock); if (!list_empty(item)) { - l = list_lru_from_kmem(lru, nid, item, NULL); + l = list_lru_from_memcg_idx(lru, nid, memcg_kmem_id(memcg)); list_del_init(item); l->nr_items--; nlru->nr_items--; @@ -160,6 +168,16 @@ bool list_lru_del(struct list_lru *lru, struct list_head *item) } EXPORT_SYMBOL_GPL(list_lru_del);

+bool list_lru_del_obj(struct list_lru *lru, struct list_head *item) +{ + int nid = page_to_nid(virt_to_page(item)); + struct mem_cgroup *memcg = list_lru_memcg_aware(lru) ? + mem_cgroup_from_slab_obj(item) : NULL; + + return list_lru_del(lru, item, nid, memcg); +} +EXPORT_SYMBOL_GPL(list_lru_del_obj); + void list_lru_isolate(struct list_lru_one *list, struct list_head *item) { list_del_init(item); @@ -175,6 +193,20 @@ void list_lru_isolate_move(struct list_lru_one *list, struct list_head *item, } EXPORT_SYMBOL_GPL(list_lru_isolate_move);

+void list_lru_putback(struct list_lru *lru, struct list_head *item, int nid, + struct mem_cgroup *memcg) +{ + struct list_lru_one *list = + list_lru_from_memcg_idx(lru, nid, memcg_kmem_id(memcg)); + + if (list_empty(item)) { + list_add_tail(item, &list->list); + if (!list->nr_items++) + set_shrinker_bit(memcg, nid, lru_shrinker_id(lru)); + } +} +EXPORT_SYMBOL_GPL(list_lru_putback); + unsigned long list_lru_count_one(struct list_lru *lru, int nid, struct mem_cgroup *memcg) { diff --git a/mm/workingset.c b/mm/workingset.c index da58a26d0d4d..bed78cf54fa4 100644 --- a/mm/workingset.c +++ b/mm/workingset.c @@ -615,12 +615,12 @@ void workingset_update_node(struct xa_node *node)

if (node->count && node->count == node->nr_values) { if (list_empty(&node->private_list)) { - list_lru_add(&shadow_nodes, &node->private_list); + list_lru_add_obj(&shadow_nodes, &node->private_list); __inc_lruvec_kmem_state(node, WORKINGSET_NODES); } } else { if (!list_empty(&node->private_list)) { - list_lru_del(&shadow_nodes, &node->private_list); + list_lru_del_obj(&shadow_nodes, &node->private_list); __dec_lruvec_kmem_state(node, WORKINGSET_NODES); } }

From: Domenico Cerasuolo cerasuolodomenico@gmail.com

mainline inclusion from mainline-v6.8-rc1 commit a65b0e7607ccb5e5184591f73e48512f25c76061 category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I8ZUJQ CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...

--------------------------------

Currently, we only have a single global LRU for zswap. This makes it impossible to perform worload-specific shrinking - an memcg cannot determine which pages in the pool it owns, and often ends up writing pages from other memcgs. This issue has been previously observed in practice and mitigated by simply disabling memcg-initiated shrinking:

https://lore.kernel.org/all/20230530232435.3097106-1-nphamcs@gmail.com/T/#u

This patch fully resolves the issue by replacing the global zswap LRU with memcg- and NUMA-specific LRUs, and modify the reclaim logic:

a) When a store attempt hits an memcg limit, it now triggers a synchronous reclaim attempt that, if successful, allows the new hotter page to be accepted by zswap. b) If the store attempt instead hits the global zswap limit, it will trigger an asynchronous reclaim attempt, in which an memcg is selected for reclaim in a round-robin-like fashion.

[nphamcs@gmail.com: use correct function for the onlineness check, use mem_cgroup_iter_break()] Link: https://lkml.kernel.org/r/20231205195419.2563217-1-nphamcs@gmail.com [nphamcs@gmail.com: drop the pool's reference at the end of the writeback step] Link: https://lkml.kernel.org/r/20231206030627.4155634-1-nphamcs@gmail.com Link: https://lkml.kernel.org/r/20231130194023.4102148-4-nphamcs@gmail.com Signed-off-by: Domenico Cerasuolo cerasuolodomenico@gmail.com Co-developed-by: Nhat Pham nphamcs@gmail.com Signed-off-by: Nhat Pham nphamcs@gmail.com Tested-by: Bagas Sanjaya bagasdotme@gmail.com Cc: Chris Li chrisl@kernel.org Cc: Dan Streetman ddstreet@ieee.org Cc: Johannes Weiner hannes@cmpxchg.org Cc: Michal Hocko mhocko@kernel.org Cc: Muchun Song muchun.song@linux.dev Cc: Roman Gushchin roman.gushchin@linux.dev Cc: Seth Jennings sjenning@redhat.com Cc: Shakeel Butt shakeelb@google.com Cc: Shuah Khan shuah@kernel.org Cc: Vitaly Wool vitaly.wool@konsulko.com Cc: Yosry Ahmed yosryahmed@google.com Signed-off-by: Andrew Morton akpm@linux-foundation.org

Conflicts: mm/swap_state.c mm/zswap.c Signed-off-by: Ma Wupeng mawupeng1@huawei.com --- include/linux/memcontrol.h | 5 + include/linux/zswap.h | 2 + mm/memcontrol.c | 3 + mm/swap.h | 3 +- mm/swap_state.c | 19 ++- mm/zswap.c | 268 ++++++++++++++++++++++++++++++------- 6 files changed, 243 insertions(+), 57 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index b0ee904aa1b5..760302ac08f7 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -1273,6 +1273,11 @@ static inline struct mem_cgroup *page_memcg_check(struct page *page) return NULL; }

+static inline struct mem_cgroup *get_mem_cgroup_from_objcg(struct obj_cgroup *objcg) +{ + return NULL; +} + static inline bool folio_memcg_kmem(struct folio *folio) { return false; diff --git a/include/linux/zswap.h b/include/linux/zswap.h index 2a60ce39cfde..e571e393669b 100644 --- a/include/linux/zswap.h +++ b/include/linux/zswap.h @@ -15,6 +15,7 @@ bool zswap_load(struct folio *folio); void zswap_invalidate(int type, pgoff_t offset); void zswap_swapon(int type); void zswap_swapoff(int type); +void zswap_memcg_offline_cleanup(struct mem_cgroup *memcg);

#else

@@ -31,6 +32,7 @@ static inline bool zswap_load(struct folio *folio) static inline void zswap_invalidate(int type, pgoff_t offset) {} static inline void zswap_swapon(int type) {} static inline void zswap_swapoff(int type) {} +static inline void zswap_memcg_offline_cleanup(struct mem_cgroup *memcg) {}

#endif

diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 346be8292294..cb5f68870c07 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -67,6 +67,7 @@ #include <linux/sched/isolation.h> #include <linux/parser.h> #include <linux/dynamic_pool.h> +#include <linux/zswap.h>

#ifdef CONFIG_MEMCG_SWAP_QOS #include <linux/blkdev.h> @@ -6543,6 +6544,8 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css) page_counter_set_min(&memcg->memory, 0); page_counter_set_low(&memcg->memory, 0);

+ zswap_memcg_offline_cleanup(memcg); + memcg_offline_kmem(memcg); reparent_shrinker_deferred(memcg); wb_memcg_offline(memcg); diff --git a/mm/swap.h b/mm/swap.h index 8a3c7a0ace4f..b54addaab860 100644 --- a/mm/swap.h +++ b/mm/swap.h @@ -50,7 +50,8 @@ struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask, struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask, struct vm_area_struct *vma, unsigned long addr, - bool *new_page_allocated); + bool *new_page_allocated, + bool skip_if_exists); struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t flag, struct vm_fault *vmf); struct page *swapin_readahead(swp_entry_t entry, gfp_t flag, diff --git a/mm/swap_state.c b/mm/swap_state.c index ddb3a65e5c6e..ceab83b90292 100644 --- a/mm/swap_state.c +++ b/mm/swap_state.c @@ -412,7 +412,7 @@ struct folio *filemap_get_incore_folio(struct address_space *mapping,

struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask, struct vm_area_struct *vma, unsigned long addr, - bool *new_page_allocated) + bool *new_page_allocated, bool skip_if_exists) { struct swap_info_struct *si; struct folio *folio; @@ -469,6 +469,17 @@ struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask, if (err != -EEXIST) goto fail_put_swap;

+ /* + * Protect against a recursive call to __read_swap_cache_async() + * on the same entry waiting forever here because SWAP_HAS_CACHE + * is set but the folio is not the swap cache yet. This can + * happen today if mem_cgroup_swapin_charge_folio() below + * triggers reclaim through zswap, which may call + * __read_swap_cache_async() in the writeback path. + */ + if (skip_if_exists) + goto fail_put_swap; + /* * We might race against __delete_from_swap_cache(), and * stumble across a swap_map entry whose SWAP_HAS_CACHE @@ -531,7 +542,7 @@ struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask, { bool page_was_allocated; struct page *retpage = __read_swap_cache_async(entry, gfp_mask, - vma, addr, &page_was_allocated); + vma, addr, &page_was_allocated, false);

if (page_was_allocated) swap_readpage(retpage, false, plug); @@ -650,7 +661,7 @@ struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask, /* Ok, do the async read-ahead now */ page = __read_swap_cache_async( swp_entry(swp_type(entry), offset), - gfp_mask, vma, addr, &page_allocated); + gfp_mask, vma, addr, &page_allocated, false); if (!page) continue; if (page_allocated) { @@ -816,7 +827,7 @@ static struct page *swap_vma_readahead(swp_entry_t fentry, gfp_t gfp_mask, pte_unmap(pte); pte = NULL; page = __read_swap_cache_async(entry, gfp_mask, vma, - addr, &page_allocated); + addr, &page_allocated, false); if (!page) continue; if (page_allocated) { diff --git a/mm/zswap.c b/mm/zswap.c index 37d2b1cb2ecb..51a2a7ddda5e 100644 --- a/mm/zswap.c +++ b/mm/zswap.c @@ -34,6 +34,7 @@ #include <linux/writeback.h> #include <linux/pagemap.h> #include <linux/workqueue.h> +#include <linux/list_lru.h>

#include "swap.h" #include "internal.h" @@ -171,8 +172,8 @@ struct zswap_pool { struct work_struct shrink_work; struct hlist_node node; char tfm_name[CRYPTO_MAX_ALG_NAME]; - struct list_head lru; - spinlock_t lru_lock; + struct list_lru list_lru; + struct mem_cgroup *next_shrink; };

/* @@ -288,15 +289,46 @@ static void zswap_update_total_size(void) zswap_pool_total_size = total; }

+/* should be called under RCU */ +#ifdef CONFIG_MEMCG +static inline struct mem_cgroup *mem_cgroup_from_entry(struct zswap_entry *entry) +{ + return entry->objcg ? obj_cgroup_memcg(entry->objcg) : NULL; +} +#else +static inline struct mem_cgroup *mem_cgroup_from_entry(struct zswap_entry *entry) +{ + return NULL; +} +#endif + +static inline int entry_to_nid(struct zswap_entry *entry) +{ + return page_to_nid(virt_to_page(entry)); +} + +void zswap_memcg_offline_cleanup(struct mem_cgroup *memcg) +{ + struct zswap_pool *pool; + + /* lock out zswap pools list modification */ + spin_lock(&zswap_pools_lock); + list_for_each_entry(pool, &zswap_pools, list) { + if (pool->next_shrink == memcg) + pool->next_shrink = mem_cgroup_iter(NULL, pool->next_shrink, NULL); + } + spin_unlock(&zswap_pools_lock); +} + /********************************* * zswap entry functions **********************************/ static struct kmem_cache *zswap_entry_cache;

-static struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp) +static struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp, int nid) { struct zswap_entry *entry; - entry = kmem_cache_alloc(zswap_entry_cache, gfp); + entry = kmem_cache_alloc_node(zswap_entry_cache, gfp, nid); if (!entry) return NULL; entry->refcount = 1; @@ -309,6 +341,61 @@ static void zswap_entry_cache_free(struct zswap_entry *entry) kmem_cache_free(zswap_entry_cache, entry); }

+/********************************* +* lru functions +**********************************/ +static void zswap_lru_add(struct list_lru *list_lru, struct zswap_entry *entry) +{ + int nid = entry_to_nid(entry); + struct mem_cgroup *memcg; + + /* + * Note that it is safe to use rcu_read_lock() here, even in the face of + * concurrent memcg offlining. Thanks to the memcg->kmemcg_id indirection + * used in list_lru lookup, only two scenarios are possible: + * + * 1. list_lru_add() is called before memcg->kmemcg_id is updated. The + * new entry will be reparented to memcg's parent's list_lru. + * 2. list_lru_add() is called after memcg->kmemcg_id is updated. The + * new entry will be added directly to memcg's parent's list_lru. + * + * Similar reasoning holds for list_lru_del() and list_lru_putback(). + */ + rcu_read_lock(); + memcg = mem_cgroup_from_entry(entry); + /* will always succeed */ + list_lru_add(list_lru, &entry->lru, nid, memcg); + rcu_read_unlock(); +} + +static void zswap_lru_del(struct list_lru *list_lru, struct zswap_entry *entry) +{ + int nid = entry_to_nid(entry); + struct mem_cgroup *memcg; + + rcu_read_lock(); + memcg = mem_cgroup_from_entry(entry); + /* will always succeed */ + list_lru_del(list_lru, &entry->lru, nid, memcg); + rcu_read_unlock(); +} + +static void zswap_lru_putback(struct list_lru *list_lru, + struct zswap_entry *entry) +{ + int nid = entry_to_nid(entry); + spinlock_t *lock = &list_lru->node[nid].lock; + struct mem_cgroup *memcg; + + rcu_read_lock(); + memcg = mem_cgroup_from_entry(entry); + spin_lock(lock); + /* we cannot use list_lru_add here, because it increments node's lru count */ + list_lru_putback(list_lru, &entry->lru, nid, memcg); + spin_unlock(lock); + rcu_read_unlock(); +} + /********************************* * rbtree functions **********************************/ @@ -393,9 +480,7 @@ static void zswap_free_entry(struct zswap_entry *entry) if (!entry->length) atomic_dec(&zswap_same_filled_pages); else { - spin_lock(&entry->pool->lru_lock); - list_del(&entry->lru); - spin_unlock(&entry->pool->lru_lock); + zswap_lru_del(&entry->pool->list_lru, entry); zpool_free(zswap_find_zpool(entry), entry->handle); zswap_pool_put(entry->pool); } @@ -629,21 +714,15 @@ static void zswap_invalidate_entry(struct zswap_tree *tree, zswap_entry_put(tree, entry); }

-static int zswap_reclaim_entry(struct zswap_pool *pool) +static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_one *l, + spinlock_t *lock, void *arg) { - struct zswap_entry *entry; + struct zswap_entry *entry = container_of(item, struct zswap_entry, lru); struct zswap_tree *tree; pgoff_t swpoffset; - int ret; + enum lru_status ret = LRU_REMOVED_RETRY; + int writeback_result;

- /* Get an entry off the LRU */ - spin_lock(&pool->lru_lock); - if (list_empty(&pool->lru)) { - spin_unlock(&pool->lru_lock); - return -EINVAL; - } - entry = list_last_entry(&pool->lru, struct zswap_entry, lru); - list_del_init(&entry->lru); /* * Once the lru lock is dropped, the entry might get freed. The * swpoffset is copied to the stack, and entry isn't deref'd again @@ -651,28 +730,32 @@ static int zswap_reclaim_entry(struct zswap_pool *pool) */ swpoffset = swp_offset(entry->swpentry); tree = zswap_trees[swp_type(entry->swpentry)]; - spin_unlock(&pool->lru_lock); + list_lru_isolate(l, item); + /* + * It's safe to drop the lock here because we return either + * LRU_REMOVED_RETRY or LRU_RETRY. + */ + spin_unlock(lock);

/* Check for invalidate() race */ spin_lock(&tree->lock); - if (entry != zswap_rb_search(&tree->rbroot, swpoffset)) { - ret = -EAGAIN; + if (entry != zswap_rb_search(&tree->rbroot, swpoffset)) goto unlock; - } + /* Hold a reference to prevent a free during writeback */ zswap_entry_get(entry); spin_unlock(&tree->lock);

- ret = zswap_writeback_entry(entry, tree); + writeback_result = zswap_writeback_entry(entry, tree);

spin_lock(&tree->lock); - if (ret) { - /* Writeback failed, put entry back on LRU */ - spin_lock(&pool->lru_lock); - list_move(&entry->lru, &pool->lru); - spin_unlock(&pool->lru_lock); + if (writeback_result) { + zswap_reject_reclaim_fail++; + zswap_lru_putback(&entry->pool->list_lru, entry); + ret = LRU_RETRY; goto put_unlock; } + zswap_written_back_pages++;

/* * Writeback started successfully, the page now belongs to the @@ -686,24 +769,91 @@ static int zswap_reclaim_entry(struct zswap_pool *pool) zswap_entry_put(tree, entry); unlock: spin_unlock(&tree->lock); - return ret ? -EAGAIN : 0; + spin_lock(lock); + return ret; +} + +static int shrink_memcg(struct mem_cgroup *memcg) +{ + struct zswap_pool *pool; + int nid, shrunk = 0; + + /* + * Skip zombies because their LRUs are reparented and we would be + * reclaiming from the parent instead of the dead memcg. + */ + if (memcg && !mem_cgroup_online(memcg)) + return -ENOENT; + + pool = zswap_pool_current_get(); + if (!pool) + return -EINVAL; + + for_each_node_state(nid, N_NORMAL_MEMORY) { + unsigned long nr_to_walk = 1; + + shrunk += list_lru_walk_one(&pool->list_lru, nid, memcg, + &shrink_memcg_cb, NULL, &nr_to_walk); + } + zswap_pool_put(pool); + return shrunk ? 0 : -EAGAIN; }

static void shrink_worker(struct work_struct *w) { struct zswap_pool *pool = container_of(w, typeof(*pool), shrink_work); + struct mem_cgroup *memcg; int ret, failures = 0;

+ /* global reclaim will select cgroup in a round-robin fashion. */ do { - ret = zswap_reclaim_entry(pool); - if (ret) { - zswap_reject_reclaim_fail++; - if (ret != -EAGAIN) + spin_lock(&zswap_pools_lock); + pool->next_shrink = mem_cgroup_iter(NULL, pool->next_shrink, NULL); + memcg = pool->next_shrink; + + /* + * We need to retry if we have gone through a full round trip, or if we + * got an offline memcg (or else we risk undoing the effect of the + * zswap memcg offlining cleanup callback). This is not catastrophic + * per se, but it will keep the now offlined memcg hostage for a while. + * + * Note that if we got an online memcg, we will keep the extra + * reference in case the original reference obtained by mem_cgroup_iter + * is dropped by the zswap memcg offlining callback, ensuring that the + * memcg is not killed when we are reclaiming. + */ + if (!memcg) { + spin_unlock(&zswap_pools_lock); + if (++failures == MAX_RECLAIM_RETRIES) break; + + goto resched; + } + + if (!mem_cgroup_tryget_online(memcg)) { + /* drop the reference from mem_cgroup_iter() */ + mem_cgroup_iter_break(NULL, memcg); + pool->next_shrink = NULL; + spin_unlock(&zswap_pools_lock); + if (++failures == MAX_RECLAIM_RETRIES) break; + + goto resched; } + spin_unlock(&zswap_pools_lock); + + ret = shrink_memcg(memcg); + /* drop the extra reference */ + mem_cgroup_put(memcg); + + if (ret == -EINVAL) + break; + if (ret && ++failures == MAX_RECLAIM_RETRIES) + break; + +resched: cond_resched(); } while (!zswap_can_accept()); zswap_pool_put(pool); @@ -764,8 +914,7 @@ static struct zswap_pool *zswap_pool_create(char *type, char *compressor) */ kref_init(&pool->kref); INIT_LIST_HEAD(&pool->list); - INIT_LIST_HEAD(&pool->lru); - spin_lock_init(&pool->lru_lock); + list_lru_init_memcg(&pool->list_lru, NULL); INIT_WORK(&pool->shrink_work, shrink_worker);

zswap_pool_debug("created", pool); @@ -831,6 +980,13 @@ static void zswap_pool_destroy(struct zswap_pool *pool)

cpuhp_state_remove_instance(CPUHP_MM_ZSWP_POOL_PREPARE, &pool->node); free_percpu(pool->acomp_ctx); + list_lru_destroy(&pool->list_lru); + + spin_lock(&zswap_pools_lock); + mem_cgroup_iter_break(NULL, pool->next_shrink); + pool->next_shrink = NULL; + spin_unlock(&zswap_pools_lock); + for (i = 0; i < ZSWAP_NR_ZPOOLS; i++) zpool_destroy_pool(pool->zpools[i]); kfree(pool); @@ -1076,7 +1232,7 @@ static int zswap_writeback_entry(struct zswap_entry *entry,

/* try to allocate swap cache page */ page = __read_swap_cache_async(swpentry, GFP_KERNEL, NULL, 0, - &page_was_allocated); + &page_was_allocated, true); if (!page) { ret = -ENOMEM; goto fail; @@ -1142,7 +1298,6 @@ static int zswap_writeback_entry(struct zswap_entry *entry, /* start writeback */ __swap_writepage(page, &wbc); put_page(page); - zswap_written_back_pages++;

return ret;

@@ -1199,6 +1354,7 @@ bool zswap_store(struct folio *folio) struct scatterlist input, output; struct crypto_acomp_ctx *acomp_ctx; struct obj_cgroup *objcg = NULL; + struct mem_cgroup *memcg = NULL; struct zswap_pool *pool; struct zpool *zpool; unsigned int dlen = PAGE_SIZE; @@ -1230,15 +1386,15 @@ bool zswap_store(struct folio *folio) zswap_invalidate_entry(tree, dupentry); } spin_unlock(&tree->lock); - - /* - * XXX: zswap reclaim does not work with cgroups yet. Without a - * cgroup-aware entry LRU, we will push out entries system-wide based on - * local cgroup limits. - */ objcg = get_obj_cgroup_from_folio(folio); - if (objcg && !obj_cgroup_may_zswap(objcg)) - goto reject; + if (objcg && !obj_cgroup_may_zswap(objcg)) { + memcg = get_mem_cgroup_from_objcg(objcg); + if (shrink_memcg(memcg)) { + mem_cgroup_put(memcg); + goto reject; + } + mem_cgroup_put(memcg); + }

/* reclaim space if needed */ if (zswap_is_full()) { @@ -1255,7 +1411,7 @@ bool zswap_store(struct folio *folio) }

/* allocate entry */ - entry = zswap_entry_cache_alloc(GFP_KERNEL); + entry = zswap_entry_cache_alloc(GFP_KERNEL, page_to_nid(page)); if (!entry) { zswap_reject_kmemcache_fail++; goto reject; @@ -1282,6 +1438,15 @@ bool zswap_store(struct folio *folio) if (!entry->pool) goto freepage;

+ if (objcg) { + memcg = get_mem_cgroup_from_objcg(objcg); + if (memcg_list_lru_alloc(memcg, &entry->pool->list_lru, GFP_KERNEL)) { + mem_cgroup_put(memcg); + goto put_pool; + } + mem_cgroup_put(memcg); + } + /* compress */ acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);

@@ -1358,9 +1523,8 @@ bool zswap_store(struct folio *folio) zswap_invalidate_entry(tree, dupentry); } if (entry->length) { - spin_lock(&entry->pool->lru_lock); - list_add(&entry->lru, &entry->pool->lru); - spin_unlock(&entry->pool->lru_lock); + INIT_LIST_HEAD(&entry->lru); + zswap_lru_add(&entry->pool->list_lru, entry); } spin_unlock(&tree->lock);

@@ -1373,6 +1537,7 @@ bool zswap_store(struct folio *folio)

put_dstmem: mutex_unlock(acomp_ctx->mutex); +put_pool: zswap_pool_put(entry->pool); freepage: zswap_entry_cache_free(entry); @@ -1467,9 +1632,8 @@ bool zswap_load(struct folio *folio) zswap_invalidate_entry(tree, entry); folio_mark_dirty(folio); } else if (entry->length) { - spin_lock(&entry->pool->lru_lock); - list_move(&entry->lru, &entry->pool->lru); - spin_unlock(&entry->pool->lru_lock); + zswap_lru_del(&entry->pool->list_lru, entry); + zswap_lru_add(&entry->pool->list_lru, entry); } zswap_entry_put(tree, entry); spin_unlock(&tree->lock);

From: Domenico Cerasuolo cerasuolodomenico@gmail.com

mainline inclusion from mainline-v6.8-rc1 commit a697dc2be925d4814f26d7588347ccdd2c5525ed category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I8ZUJQ CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...

--------------------------------

The memcg-zswap self test is updated to adjust to the behavior change implemented by commit 87730b165089 ("zswap: make shrinking memcg-aware"), where zswap performs writeback for specific memcg.

Link: https://lkml.kernel.org/r/20231130194023.4102148-6-nphamcs@gmail.com Signed-off-by: Domenico Cerasuolo cerasuolodomenico@gmail.com Signed-off-by: Nhat Pham nphamcs@gmail.com Tested-by: Bagas Sanjaya bagasdotme@gmail.com Acked-by: Chris Li chrisl@kernel.org (Google) Cc: Dan Streetman ddstreet@ieee.org Cc: Johannes Weiner hannes@cmpxchg.org Cc: Michal Hocko mhocko@kernel.org Cc: Muchun Song muchun.song@linux.dev Cc: Roman Gushchin roman.gushchin@linux.dev Cc: Seth Jennings sjenning@redhat.com Cc: Shakeel Butt shakeelb@google.com Cc: Shuah Khan shuah@kernel.org Cc: Vitaly Wool vitaly.wool@konsulko.com Cc: Yosry Ahmed yosryahmed@google.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Ma Wupeng mawupeng1@huawei.com --- tools/testing/selftests/cgroup/test_zswap.c | 74 ++++++++++++++------- 1 file changed, 50 insertions(+), 24 deletions(-)

diff --git a/tools/testing/selftests/cgroup/test_zswap.c b/tools/testing/selftests/cgroup/test_zswap.c index 49def87a909b..753a3b9de1ad 100644 --- a/tools/testing/selftests/cgroup/test_zswap.c +++ b/tools/testing/selftests/cgroup/test_zswap.c @@ -50,9 +50,9 @@ static int get_zswap_stored_pages(size_t *value) return read_int("/sys/kernel/debug/zswap/stored_pages", value); }

-static int get_zswap_written_back_pages(size_t *value) +static int get_cg_wb_count(const char *cg) { - return read_int("/sys/kernel/debug/zswap/written_back_pages", value); + return cg_read_key_long(cg, "memory.stat", "zswp_wb"); }

static int allocate_bytes(const char *cgroup, void *arg) @@ -68,45 +68,71 @@ static int allocate_bytes(const char *cgroup, void *arg) return 0; }

+static char *setup_test_group_1M(const char *root, const char *name) +{ + char *group_name = cg_name(root, name); + + if (!group_name) + return NULL; + if (cg_create(group_name)) + goto fail; + if (cg_write(group_name, "memory.max", "1M")) { + cg_destroy(group_name); + goto fail; + } + return group_name; +fail: + free(group_name); + return NULL; +} + /* * When trying to store a memcg page in zswap, if the memcg hits its memory - * limit in zswap, writeback should not be triggered. - * - * This was fixed with commit 0bdf0efa180a("zswap: do not shrink if cgroup may - * not zswap"). Needs to be revised when a per memcg writeback mechanism is - * implemented. + * limit in zswap, writeback should affect only the zswapped pages of that + * memcg. */ static int test_no_invasive_cgroup_shrink(const char *root) { - size_t written_back_before, written_back_after; int ret = KSFT_FAIL; - char *test_group; + size_t control_allocation_size = MB(10); + char *control_allocation, *wb_group = NULL, *control_group = NULL;

/* Set up */ - test_group = cg_name(root, "no_shrink_test"); - if (!test_group) - goto out; - if (cg_create(test_group)) + wb_group = setup_test_group_1M(root, "per_memcg_wb_test1"); + if (!wb_group) + return KSFT_FAIL; + if (cg_write(wb_group, "memory.zswap.max", "10K")) goto out; - if (cg_write(test_group, "memory.max", "1M")) + control_group = setup_test_group_1M(root, "per_memcg_wb_test2"); + if (!control_group) goto out; - if (cg_write(test_group, "memory.zswap.max", "10K")) + + /* Push some test_group2 memory into zswap */ + if (cg_enter_current(control_group)) goto out; - if (get_zswap_written_back_pages(&written_back_before)) + control_allocation = malloc(control_allocation_size); + for (int i = 0; i < control_allocation_size; i += 4095) + control_allocation[i] = 'a'; + if (cg_read_key_long(control_group, "memory.stat", "zswapped") < 1) goto out;

- /* Allocate 10x memory.max to push memory into zswap */ - if (cg_run(test_group, allocate_bytes, (void *)MB(10))) + /* Allocate 10x memory.max to push wb_group memory into zswap and trigger wb */ + if (cg_run(wb_group, allocate_bytes, (void *)MB(10))) goto out;

- /* Verify that no writeback happened because of the memcg allocation */ - if (get_zswap_written_back_pages(&written_back_after)) - goto out; - if (written_back_after == written_back_before) + /* Verify that only zswapped memory from gwb_group has been written back */ + if (get_cg_wb_count(wb_group) > 0 && get_cg_wb_count(control_group) == 0) ret = KSFT_PASS; out: - cg_destroy(test_group); - free(test_group); + cg_enter_current(root); + if (control_group) { + cg_destroy(control_group); + free(control_group); + } + cg_destroy(wb_group); + free(wb_group); + if (control_allocation) + free(control_allocation); return ret; }

From: Nhat Pham nphamcs@gmail.com

mainline inclusion from mainline-v6.8-rc1 commit 501a06fe8e4c185bbda371b8cedbdf1b23a633d8 category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I8ZUJQ CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...

--------------------------------

During our experiment with zswap, we sometimes observe swap IOs due to occasional zswap store failures and writebacks-to-swap. These swapping IOs prevent many users who cannot tolerate swapping from adopting zswap to save memory and improve performance where possible.

This patch adds the option to disable this behavior entirely: do not writeback to backing swapping device when a zswap store attempt fail, and do not write pages in the zswap pool back to the backing swap device (both when the pool is full, and when the new zswap shrinker is called).

This new behavior can be opted-in/out on a per-cgroup basis via a new cgroup file. By default, writebacks to swap device is enabled, which is the previous behavior. Initially, writeback is enabled for the root cgroup, and a newly created cgroup will inherit the current setting of its parent.

Note that this is subtly different from setting memory.swap.max to 0, as it still allows for pages to be stored in the zswap pool (which itself consumes swap space in its current form).

This patch should be applied on top of the zswap shrinker series:

https://lore.kernel.org/linux-mm/20231130194023.4102148-1-nphamcs@gmail.com/

as it also disables the zswap shrinker, a major source of zswap writebacks.

For the most part, this feature is motivated by internal parties who have already established their opinions regarding swapping - the workloads that are highly sensitive to IO, and especially those who are using servers with really slow disk performance (for instance, massive but slow HDDs). For these folks, it's impossible to convince them to even entertain zswap if swapping also comes as a packaged deal. Writeback disabling is quite a useful feature in these situations - on a mixed workloads deployment, they can disable writeback for the more IO-sensitive workloads, and enable writeback for other background workloads.

For instance, on a server with HDD, I allocate memories and populate them with random values (so that zswap store will always fail), and specify memory.high low enough to trigger reclaim. The time it takes to allocate the memories and just read through it a couple of times (doing silly things like computing the values' average etc.):

zswap.writeback disabled: real 0m30.537s user 0m23.687s sys 0m6.637s 0 pages swapped in 0 pages swapped out

zswap.writeback enabled: real 0m45.061s user 0m24.310s sys 0m8.892s 712686 pages swapped in 461093 pages swapped out

(the last two lines are from vmstat -s).

[nphamcs@gmail.com: add a comment about recurring zswap store failures leading to reclaim inefficiency] Link: https://lkml.kernel.org/r/20231221005725.3446672-1-nphamcs@gmail.com Link: https://lkml.kernel.org/r/20231207192406.3809579-1-nphamcs@gmail.com Signed-off-by: Nhat Pham nphamcs@gmail.com Suggested-by: Johannes Weiner hannes@cmpxchg.org Reviewed-by: Yosry Ahmed yosryahmed@google.com Acked-by: Chris Li chrisl@kernel.org Cc: Dan Streetman ddstreet@ieee.org Cc: David Heidelberg david@ixit.cz Cc: Domenico Cerasuolo cerasuolodomenico@gmail.com Cc: Hugh Dickins hughd@google.com Cc: Jonathan Corbet corbet@lwn.net Cc: Konrad Rzeszutek Wilk konrad.wilk@oracle.com Cc: Michal Hocko mhocko@kernel.org Cc: Mike Rapoport (IBM) rppt@kernel.org Cc: Muchun Song muchun.song@linux.dev Cc: Roman Gushchin roman.gushchin@linux.dev Cc: Sergey Senozhatsky senozhatsky@chromium.org Cc: Seth Jennings sjenning@redhat.com Cc: Shakeel Butt shakeelb@google.com Cc: Tejun Heo tj@kernel.org Cc: Vitaly Wool vitaly.wool@konsulko.com Cc: Zefan Li lizefan.x@bytedance.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Ma Wupeng mawupeng1@huawei.com --- Documentation/admin-guide/cgroup-v2.rst | 15 ++++++++++ Documentation/admin-guide/mm/zswap.rst | 10 +++++++ include/linux/memcontrol.h | 12 ++++++++ include/linux/zswap.h | 5 ++++ mm/memcontrol.c | 38 +++++++++++++++++++++++++ mm/page_io.c | 6 ++++ mm/shmem.c | 3 +- mm/zswap.c | 13 +++++++-- 8 files changed, 98 insertions(+), 4 deletions(-)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst index e998aa071ced..45a8b6743352 100644 --- a/Documentation/admin-guide/cgroup-v2.rst +++ b/Documentation/admin-guide/cgroup-v2.rst @@ -1645,6 +1645,21 @@ PAGE_SIZE multiple when read back. limit, it will refuse to take any more stores before existing entries fault back in or are written out to disk.

+ memory.zswap.writeback + A read-write single value file. The default value is "1". The + initial value of the root cgroup is 1, and when a new cgroup is + created, it inherits the current value of its parent. + + When this is set to 0, all swapping attempts to swapping devices + are disabled. This included both zswap writebacks, and swapping due + to zswap store failures. If the zswap store failures are recurring + (for e.g if the pages are incompressible), users can observe + reclaim inefficiency after disabling writeback (because the same + pages might be rejected again and again). + + Note that this is subtly different from setting memory.swap.max to + 0, as it still allows for pages to be written to the zswap pool. + memory.pressure A read-only nested-keyed file.

diff --git a/Documentation/admin-guide/mm/zswap.rst b/Documentation/admin-guide/mm/zswap.rst index 62fc244ec702..b42132969e31 100644 --- a/Documentation/admin-guide/mm/zswap.rst +++ b/Documentation/admin-guide/mm/zswap.rst @@ -153,6 +153,16 @@ attribute, e. g.::

Setting this parameter to 100 will disable the hysteresis.

+Some users cannot tolerate the swapping that comes with zswap store failures +and zswap writebacks. Swapping can be disabled entirely (without disabling +zswap itself) on a cgroup-basis as follows: + + echo 0 > /sys/fs/cgroup/<cgroup-name>/memory.zswap.writeback + +Note that if the store failures are recurring (for e.g if the pages are +incompressible), users can observe reclaim inefficiency after disabling +writeback (because the same pages might be rejected again and again). + When there is a sizable amount of cold memory residing in the zswap pool, it can be advantageous to proactively write these cold pages to swap and reclaim the memory for other use cases. By default, the zswap shrinker is disabled. diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 760302ac08f7..d9b910fac70b 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -241,6 +241,12 @@ struct mem_cgroup {

#if defined(CONFIG_MEMCG_KMEM) && defined(CONFIG_ZSWAP) unsigned long zswap_max; + + /* + * Prevent pages from this memcg from being written back from zswap to + * swap, and from being swapped out on zswap store failures. + */ + bool zswap_writeback; #endif

unsigned long soft_limit; @@ -1996,6 +2002,7 @@ static inline void count_objcg_event(struct obj_cgroup *objcg, bool obj_cgroup_may_zswap(struct obj_cgroup *objcg); void obj_cgroup_charge_zswap(struct obj_cgroup *objcg, size_t size); void obj_cgroup_uncharge_zswap(struct obj_cgroup *objcg, size_t size); +bool mem_cgroup_zswap_writeback_enabled(struct mem_cgroup *memcg); #else static inline bool obj_cgroup_may_zswap(struct obj_cgroup *objcg) { @@ -2009,6 +2016,11 @@ static inline void obj_cgroup_uncharge_zswap(struct obj_cgroup *objcg, size_t size) { } +static inline bool mem_cgroup_zswap_writeback_enabled(struct mem_cgroup *memcg) +{ + /* if zswap is disabled, do not block pages going to the swapping device */ + return true; +} #endif

#endif /* _LINUX_MEMCONTROL_H */ diff --git a/include/linux/zswap.h b/include/linux/zswap.h index 08c240e16a01..f0f6d8a04c81 100644 --- a/include/linux/zswap.h +++ b/include/linux/zswap.h @@ -35,6 +35,7 @@ void zswap_swapoff(int type); void zswap_memcg_offline_cleanup(struct mem_cgroup *memcg); void zswap_lruvec_state_init(struct lruvec *lruvec); void zswap_page_swapin(struct page *page); +bool is_zswap_enabled(void); #else

struct zswap_lruvec_state {}; @@ -55,6 +56,10 @@ static inline void zswap_swapoff(int type) {} static inline void zswap_memcg_offline_cleanup(struct mem_cgroup *memcg) {} static inline void zswap_lruvec_state_init(struct lruvec *lruvec) {} static inline void zswap_page_swapin(struct page *page) {} +static inline bool is_zswap_enabled(void) +{ + return false; +} #endif

#endif /* _LINUX_ZSWAP_H */ diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 9d8092048603..8e3dd875a4ae 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -6437,6 +6437,8 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css) WRITE_ONCE(memcg->soft_limit, PAGE_COUNTER_MAX); #if defined(CONFIG_MEMCG_KMEM) && defined(CONFIG_ZSWAP) memcg->zswap_max = PAGE_COUNTER_MAX; + WRITE_ONCE(memcg->zswap_writeback, + !parent || READ_ONCE(parent->zswap_writeback)); #endif #ifdef CONFIG_MEMCG_V1_RECLAIM memcg->high_async_ratio = HIGH_ASYNC_RATIO_BASE; @@ -9052,6 +9054,12 @@ void obj_cgroup_uncharge_zswap(struct obj_cgroup *objcg, size_t size) rcu_read_unlock(); }

+bool mem_cgroup_zswap_writeback_enabled(struct mem_cgroup *memcg) +{ + /* if zswap is disabled, do not block pages going to the swapping device */ + return !is_zswap_enabled() || !memcg || READ_ONCE(memcg->zswap_writeback); +} + static u64 zswap_current_read(struct cgroup_subsys_state *css, struct cftype *cft) { @@ -9082,6 +9090,31 @@ static ssize_t zswap_max_write(struct kernfs_open_file *of, return nbytes; }

+static int zswap_writeback_show(struct seq_file *m, void *v) +{ + struct mem_cgroup *memcg = mem_cgroup_from_seq(m); + + seq_printf(m, "%d\n", READ_ONCE(memcg->zswap_writeback)); + return 0; +} + +static ssize_t zswap_writeback_write(struct kernfs_open_file *of, + char *buf, size_t nbytes, loff_t off) +{ + struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of)); + int zswap_writeback; + ssize_t parse_ret = kstrtoint(strstrip(buf), 0, &zswap_writeback); + + if (parse_ret) + return parse_ret; + + if (zswap_writeback != 0 && zswap_writeback != 1) + return -EINVAL; + + WRITE_ONCE(memcg->zswap_writeback, zswap_writeback); + return nbytes; +} + static struct cftype zswap_files[] = { { .name = "zswap.current", @@ -9094,6 +9127,11 @@ static struct cftype zswap_files[] = { .seq_show = zswap_max_show, .write = zswap_max_write, }, + { + .name = "zswap.writeback", + .seq_show = zswap_writeback_show, + .write = zswap_writeback_write, + }, { } /* terminate */ }; #endif /* CONFIG_MEMCG_KMEM && CONFIG_ZSWAP */ diff --git a/mm/page_io.c b/mm/page_io.c index af65db0be731..d7defb114b34 100644 --- a/mm/page_io.c +++ b/mm/page_io.c @@ -201,6 +201,12 @@ int swap_writepage(struct page *page, struct writeback_control *wbc) folio_end_writeback(folio); return 0; } + + if (!mem_cgroup_zswap_writeback_enabled(folio_memcg(folio))) { + folio_mark_dirty(folio); + return AOP_WRITEPAGE_ACTIVATE; + } + __swap_writepage(&folio->page, wbc); return 0; } diff --git a/mm/shmem.c b/mm/shmem.c index de9a884b10e8..d4ecbd131c01 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -1521,8 +1521,7 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)

mutex_unlock(&shmem_swaplist_mutex); BUG_ON(folio_mapped(folio)); - swap_writepage(&folio->page, wbc); - return 0; + return swap_writepage(&folio->page, wbc); }

mutex_unlock(&shmem_swaplist_mutex); diff --git a/mm/zswap.c b/mm/zswap.c index 2146f2dad4cd..894ccae11a39 100644 --- a/mm/zswap.c +++ b/mm/zswap.c @@ -150,6 +150,11 @@ static bool zswap_shrinker_enabled = IS_ENABLED( CONFIG_ZSWAP_SHRINKER_DEFAULT_ON); module_param_named(shrinker_enabled, zswap_shrinker_enabled, bool, 0644);

+bool is_zswap_enabled(void) +{ + return zswap_enabled; +} + /********************************* * data structures **********************************/ @@ -593,7 +598,8 @@ static unsigned long zswap_shrinker_scan(struct shrinker *shrinker, struct zswap_pool *pool = container_of(shrinker, struct zswap_pool, shrinker); bool encountered_page_in_swapcache = false;

- if (!zswap_shrinker_enabled) { + if (!zswap_shrinker_enabled || + !mem_cgroup_zswap_writeback_enabled(sc->memcg)) { sc->nr_scanned = 0; return SHRINK_STOP; } @@ -634,7 +640,7 @@ static unsigned long zswap_shrinker_count(struct shrinker *shrinker, struct lruvec *lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(sc->nid)); unsigned long nr_backing, nr_stored, nr_freeable, nr_protected;

- if (!zswap_shrinker_enabled) + if (!zswap_shrinker_enabled || !mem_cgroup_zswap_writeback_enabled(memcg)) return 0;

#ifdef CONFIG_MEMCG_KMEM @@ -950,6 +956,9 @@ static int shrink_memcg(struct mem_cgroup *memcg) struct zswap_pool *pool; int nid, shrunk = 0;

+ if (!mem_cgroup_zswap_writeback_enabled(memcg)) + return -EINVAL; + /* * Skip zombies because their LRUs are reparented and we would be * reclaiming from the parent instead of the dead memcg.