[PATCH openEuler-1.0-LTS 0/2] mm: introduce ZRAM-Reclaim module for optimized swap-based reclaim
In ZRAM + HDD storage environments, the default LRU-based reclaim policy often struggles to effectively balance anonymous and file-backed pages. The existing algorithm tends to over-reclaim file pages under memory pressure, causing excessive disk I/O and poor system responsiveness when ZRAM is used as a compressed swap device. The historical VM assumption treats anonymous pages as "expensive" to reclaim (requires swap I/O) and file pages as "cheap" (just drop clean cache). However, this assumption is inverted for ZRAM + slow disk scenarios: reclaiming anonymous pages from ZRAM (decompress + discard) is significantly cheaper than reclaiming file pages which may require disk reads to fault back in. This series introduces CONFIG_ZRAM_RECLAIM, a new reclaim policy module that addresses this problem through: 1) Per-lruvec refault cost tracking for anonymous and file pages 2) Dynamic scan balancing based on observed refault pressure 3) CPU vendor auto-tuning for Hisilicon ARM64 platforms The key observation is that when anonymous pages are being refaulted frequently while file pages are not, the system should prioritize reclaiming anonymous pages (which are cheap to re-fault from ZRAM) over file pages (which are expensive to read from disk). Implementation overview: Patch 1 adds the core infrastructure: Kconfig option, mem_cgroup extensions, cost tracking counters, and the scan balancing logic. Patch 2 hooks the module into existing VM paths: do_swap_page for anonymous refaults, workingset_refault for file refaults, and get_scan_count for reclaim decisions. The feature depends on MEMCG and is controlled by the per-memcg 'more_zram' flag, allowing fine-grained control per cgroup. Testing on Hisilicon TSV200 platform with ZRAM as swap device shows significant reduction in file page thrashing and improved application launch times under memory pressure. Ze Zuo (2): mm: add ZRAM-Reclaim infrastructure and policy core mm: hook ZRAM-Reclaim into swap and refault paths include/linux/memcontrol.h | 6 + include/linux/zram_reclaim.h | 25 ++++ mm/Kconfig | 9 ++ mm/Makefile | 1 + mm/memory.c | 8 ++ mm/vmscan.c | 6 + mm/workingset.c | 3 + mm/zram_reclaim.c | 244 +++++++++++++++++++++++++++++++++++ 8 files changed, 302 insertions(+) create mode 100644 include/linux/zram_reclaim.h create mode 100644 mm/zram_reclaim.c -- 2.33.0
Introduce CONFIG_ZRAM_RECLAIM, a new configurable reclaim module optimized for ZRAM + HDD environments. This patch adds the core infrastructure including Kconfig option, data structures, cost tracking counters, and the main policy logic. Data structure changes: - Extend struct mem_cgroup with conditionally compiled fields: 'more_zram' flag to indicate ZRAM-heavy workload 'zram_limit_ratio' for future limit control 'anon_cost' and 'file_cost' for tracking refault pressure - struct mem_cgroup_per_node is not directly extended; instead, per-lruvec cost counters are stored in the existing lruvec structure through atomic_long_t fields. The nodeinfo array remains the last member of mem_cgroup for ABI compatibility. Core policy logic: - zram_reclaim_balance_scan(): called from get_scan_count() to dynamically adjust reclaim scan balance. When 'more_zram' is set, it checks if anonymous refault pressure exceeds thresholds: threshold = max(5000UL, total_anon >> 10) overloaded = (anon_cost > threshold) && (anon_cost > file_cost * weight + 1) If overloaded, swappiness is forced to 150 and function returns false to let normal scan proceed with elevated swappiness. Otherwise, returns true to skip balance logic. Cost tracking (to be hooked in patch 2): - zram_reclaim_refault_cost() records refault events for file pages - Similar helper for anon pages called from do_swap_page - Counters decay automatically: when anon_cost + file_cost exceeds total_lruvec_size >> 10, both counters are halved CPU vendor auto-tuning: - On ARM64 with Hisilicon CPUs, automatically initialize zram_file_weight_default based on CPU part number: TSV110: weight = 64 TSV200+: weight = 100 - The weight controls the threshold for overload detection - Uses early_initcall() to run before other mm initializations The feature depends on MEMCG and adds no overhead when CONFIG_ZRAM_RECLAIM is disabled. Signed-off-by: Ze Zuo <zuoze1@huawei.com> Signed-off-by: Nanyong Sun <sunnanyong@huawei.com> --- include/linux/memcontrol.h | 6 + include/linux/zram_reclaim.h | 25 ++++ mm/Kconfig | 9 ++ mm/Makefile | 1 + mm/zram_reclaim.c | 244 +++++++++++++++++++++++++++++++++++ 5 files changed, 285 insertions(+) create mode 100644 include/linux/zram_reclaim.h create mode 100644 mm/zram_reclaim.c diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 9e4d2fbc3..9eabc7179 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -346,6 +346,12 @@ struct mem_cgroup_extension { spinlock_t split_queue_lock; struct list_head split_queue; unsigned long split_queue_len; +#ifdef CONFIG_ZRAM_RECLAIM + unsigned int zram_reclaim; + unsigned int zram_limit_ratio; + atomic_long_t anon_cost; + atomic_long_t file_cost; +#endif struct mem_cgroup memcg; }; diff --git a/include/linux/zram_reclaim.h b/include/linux/zram_reclaim.h new file mode 100644 index 000000000..e820201b5 --- /dev/null +++ b/include/linux/zram_reclaim.h @@ -0,0 +1,25 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _LINUX_ZRAM_RECLAIM_H +#define _LINUX_ZRAM_RECLAIM_H + +#include <linux/memcontrol.h> + +#ifdef CONFIG_ZRAM_RECLAIM +void zram_reclaim_refault_cost(struct mem_cgroup *memcg, struct lruvec *lruvec, + bool file, unsigned long nr_pages); + +bool zram_reclaim_scan_balance(struct lruvec *lruvec, struct mem_cgroup *memcg, + int *swappiness); +#else +static inline void zram_reclaim_refault_cost(struct mem_cgroup *memcg, + struct lruvec *lruvec, + bool file, + unsigned long nr_pages) +{ } + +static inline bool zram_reclaim_scan_balance(struct lruvec *lruvec, + struct mem_cgroup *memcg, + int *swappiness) +{ return false; } +#endif +#endif /* _LINUX_ZRAM_RECLAIM_H */ diff --git a/mm/Kconfig b/mm/Kconfig index e607d1576..71ff835a2 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -528,6 +528,15 @@ config MEMCG_QOS If unsure, say "n". + +config ZRAM_RECLAIM + bool "Optimized Reclaim Policy for ZRAM Environments" + depends on MEMCG + help + Enable advanced memory reclaim strategy for ZRAM + HDD environments. + Isolates the custom policy logic into a separate module, supporting + CPU-based auto-tuning (e.g., HISI) and proactive anon reclaim. + config CMA bool "Contiguous Memory Allocator" depends on HAVE_MEMBLOCK && MMU diff --git a/mm/Makefile b/mm/Makefile index 7f19e97ce..bb4646ad9 100644 --- a/mm/Makefile +++ b/mm/Makefile @@ -111,3 +111,4 @@ obj-$(CONFIG_ASCEND_SHARE_POOL) += share_pool.o obj-$(CONFIG_MEMCG_MEMFS_INFO) += memcg_memfs_info.o obj-$(CONFIG_MEMORY_RELIABLE) += mem_reliable.o obj-$(CONFIG_CLEAR_FREELIST_PAGE) += clear_freelist_page.o +obj-$(CONFIG_ZRAM_RECLAIM) += zram_reclaim.o diff --git a/mm/zram_reclaim.c b/mm/zram_reclaim.c new file mode 100644 index 000000000..215b734d0 --- /dev/null +++ b/mm/zram_reclaim.c @@ -0,0 +1,244 @@ +// SPDX-License-Identifier: GPL-2.0 +#include <linux/zram_reclaim.h> + +static unsigned int zram_file_weight_default; +static unsigned int zram_fallback_swappiness; + +/** + * zram_reclaim_refault_cost - Record IO reclaim cost and decay historical + * data dynamically. + * @mem_cgroup: The mem_cgroup to update. + * @file: True if file page cost, false if anon page cost. + * @nr_pages: Number of pages involved in the cost event. + */ +void zram_reclaim_refault_cost(struct mem_cgroup *memcg, struct lruvec *lruvec, + bool file, unsigned long nr_pages) +{ + unsigned long a, f, total; + struct mem_cgroup_extension *memcg_ext; + + if (!memcg) + return; + + memcg_ext = to_memcg_ext(memcg); + if (!memcg_ext->zram_reclaim) + return; + + if (file) + atomic_long_add(nr_pages, &memcg_ext->file_cost); + else + atomic_long_add(nr_pages, &memcg_ext->anon_cost); + + a = atomic_long_read(&memcg_ext->anon_cost); + f = atomic_long_read(&memcg_ext->file_cost); + + total = lruvec_lru_size(lruvec, LRU_INACTIVE_ANON, MAX_NR_ZONES) + + lruvec_lru_size(lruvec, LRU_ACTIVE_ANON, MAX_NR_ZONES) + + lruvec_lru_size(lruvec, LRU_INACTIVE_FILE, MAX_NR_ZONES) + + lruvec_lru_size(lruvec, LRU_ACTIVE_FILE, MAX_NR_ZONES); + + if (a + f > (total >> 2)) { + atomic_long_sub(a >> 1, &memcg_ext->anon_cost); + atomic_long_sub(f >> 1, &memcg_ext->file_cost); + } +} + +bool zram_reclaim_scan_balance(struct lruvec *lruvec, + struct mem_cgroup *memcg, + int *swappiness) +{ + bool zram_overloaded; + unsigned int abs, weight = zram_file_weight_default; + struct mem_cgroup_extension *memcg_ext; + unsigned long total_anon, total_file, a_cost, f_cost; + + if (!memcg || !weight) + return false; + + memcg_ext = to_memcg_ext(memcg); + if (!memcg_ext->zram_reclaim) + return false; + + a_cost = atomic_long_read(&memcg_ext->anon_cost); + f_cost = atomic_long_read(&memcg_ext->file_cost); + + /* + * Workload Classifier: Avoid forcing ANON reclaim when anon is scarce + * (total_anon < total_file / 2). Prevents this cgroup from becoming + * a "memory black hole" that starves other cgroups of reclaim pressure. + */ + total_anon = lruvec_lru_size(lruvec, LRU_ACTIVE_ANON, MAX_NR_ZONES) + + lruvec_lru_size(lruvec, LRU_INACTIVE_ANON, MAX_NR_ZONES); + total_file = lruvec_lru_size(lruvec, LRU_ACTIVE_FILE, MAX_NR_ZONES) + + lruvec_lru_size(lruvec, LRU_INACTIVE_FILE, MAX_NR_ZONES); + + /* + * Cost threshold: 0.1% of total_anon (min 5000). For 400GB cgroup, + * this is ~3s ZRAM latency, enough to absorb concurrency spikes. + */ + abs = max(5000UL, total_anon >> 10); + + /* Skip aggressive strategy for Cache-heavy workloads */ + if (total_anon * 2 < total_file) + return false; + + /* + * Check ZRAM usage ratio limit to prevent ZRAM exhaustion. + * + * For cgroups with swap accounting enabled, calculate the actual + * swap usage: + * nr_swap = memsw - memory + * swap_ratio = nr_swap / (nr_swap + total_anon) * 100 + * + * If swap_ratio exceeds zram_limit_ratio, fallback to default balance + * (stop aggressive SCAN_ANON). + */ + if (do_swap_account) { + unsigned int limit = READ_ONCE(memcg_ext->zram_limit_ratio); + + if (!limit) + return false; + + unsigned long nr_mem = page_counter_read(&memcg->memory); + unsigned long nr_swap_total = page_counter_read(&memcg->memsw); + + if (nr_swap_total <= nr_mem) + return false; + + unsigned long nr_swap = nr_swap_total - nr_mem; + unsigned long total = nr_swap + total_anon; + + if (total && (u64)nr_swap * 100 > (u64)limit * total) + return false; + } + + /* + * Double Gate: Force SCAN_ANON only when both conditions hold: + * 1. Absolute overload: anon_cost > 0.1% of total_anon (abs_thresh) + * 2. Relative pain: anon_cost > file_cost * weight (ZRAM worse + * than HDD) + */ + zram_overloaded = (a_cost > abs) && (a_cost > f_cost * weight + 1); + + if (!zram_overloaded) + return true; + + *swappiness = zram_fallback_swappiness ?: 150; + + return false; +} + +static int memory_zram_reclaim_show(struct seq_file *m, void *v) +{ + struct mem_cgroup *memcg = mem_cgroup_from_css(seq_css(m)); + struct mem_cgroup_extension *memcg_ext = to_memcg_ext(memcg); + + if (memcg_ext->zram_reclaim) + seq_printf(m, "1 %u\n", memcg_ext->zram_limit_ratio); + else + seq_printf(m, "%u\n", memcg_ext->zram_limit_ratio); + return 0; +} + +static ssize_t memory_zram_reclaim_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)); + struct mem_cgroup_extension *memcg_ext = to_memcg_ext(memcg); + char *token; + unsigned long enable; + unsigned long ratio = 0; + int ret; + + if (!zram_file_weight_default) + return -EOPNOTSUPP; + + /* Parse first token (enable) */ + token = strsep(&buf, " \t"); + if (!token) + return -EINVAL; + + ret = kstrtoul(token, 0, &enable); + if (ret) + return ret; + + if (enable != 0 && enable != 1) + return -EINVAL; + + /* Parse second token (ratio) if exists */ + if (buf) { + token = strstrip(buf); + if (token && *token) { + ret = kstrtoul(token, 0, &ratio); + if (ret) + return ret; + if (ratio == 0 || ratio > 100) + return -EINVAL; + } + } + + /* Handle disable */ + if (enable == 0) { + memcg_ext->zram_reclaim = 0; + return nbytes; + } + + /* Handle enable */ + if (ratio == 0) { + /* echo 1 (no ratio specified): use default 30 */ + ratio = 30; + } + + /* + * Dynamic update restriction: + * Cannot change ratio while already enabled + */ + if (memcg_ext->zram_reclaim && ratio != memcg_ext->zram_limit_ratio) { + pr_warn("Disable zram_reclaim first (write 0) to change limit ratio.\n"); + return -EBUSY; + } + + /* Apply new settings */ + memcg_ext->zram_reclaim = 1; + memcg_ext->zram_limit_ratio = ratio; + + return nbytes; +} + +static int __init zram_reclaim_sysfs_init(void) +{ + static struct cftype zram_files[] = { + { + .name = "zram_reclaim", + .flags = CFTYPE_NOT_ON_ROOT, + .seq_show = memory_zram_reclaim_show, + .write = memory_zram_reclaim_write, + }, + { }, + }; + return cgroup_add_legacy_cftypes(&memory_cgrp_subsys, zram_files); +} +subsys_initcall(zram_reclaim_sysfs_init); + +static int __init zram_reclaim_init(void) +{ +#ifdef CONFIG_ARM64 + u64 midr = read_cpuid_id(); + + /* Based on latency measurements (HDD ~10ms vs ZRAM ~3-10us), + * one HDD Refault costs roughly 100 times as much as a ZRAM SwapIn. + * Update the default penalty factor to better reflect this gap and + * prevent the strategy from giving up on ZRAM protection too early. + */ + if (MIDR_IMPLEMENTOR(midr) == ARM_CPU_IMP_HISI) { + u32 part = MIDR_PARTNUM(midr); + + if (part == HISI_CPU_PART_TSV110) + zram_file_weight_default = 64; + else if (part >= HISI_CPU_PART_TSV200) + zram_file_weight_default = 100; + } +#endif + return 0; +} +early_initcall(zram_reclaim_init); -- 2.33.0
Integrate the ZRAM-Reclaim module with core VM paths to enable real-time refault tracking and dynamic scan balance adjustments. Three key hooks are added: 1) Anonymous refault tracking in do_swap_page(): When a swapped-out anonymous page is faulted back in, record a cost event for anonymous pages. This indicates that anonymous memory is actively being used and reclaiming it would incur a decompression cost on refault. 2) File refault tracking in workingset_refault(): When a file page is reactivated from the shadow entries, record a cost event for file pages. This indicates file cache pressure and helps detect when file pages are being thrashed. 3) Scan balance integration in get_scan_count(): Call zram_reclaim_balance_scan() before making scan balance decisions. If the function returns true, skip the default balance logic and set scan_balance = SCAN_ANON. The function may also modify swappiness internally when overload conditions are detected. The tracking uses zram_reclaim_refault_cost() (named lru_note_cost in the original implementation) to update the per-lruvec anon_cost and file_cost counters. These counters are then used by the policy logic introduced in patch 1 to determine if anonymous refault pressure exceeds thresholds. Implementation notes: - The workingset_refault and do_swap_page hooks are guarded by CONFIG_ZRAM_RECLAIM to avoid overhead when the feature is disabled - Each swap-in or refault operation records a cost of 1 page - The lruvec and memcg are looked up from the page and pgdat Signed-off-by: Ze Zuo <zuoze1@huawei.com> Signed-off-by: Nanyong Sun <sunnanyong@huawei.com> --- mm/memory.c | 8 ++++++++ mm/vmscan.c | 6 ++++++ mm/workingset.c | 3 +++ 3 files changed, 17 insertions(+) diff --git a/mm/memory.c b/mm/memory.c index a54204f0f..737ec36ac 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -71,6 +71,7 @@ #include <linux/oom.h> #include <linux/ktask.h> #include <linux/share_pool.h> +#include <linux/zram_reclaim.h> #include <asm/io.h> #include <asm/mmu_context.h> @@ -3068,6 +3069,13 @@ skip_uswap: goto out_page; } +#ifdef CONFIG_ZRAM_RECLAIM + if (memcg) + zram_reclaim_refault_cost(memcg, + mem_cgroup_lruvec(page_pgdat(page), memcg), + false, 1); +#endif + /* * Back out if somebody else already faulted in this pte. */ diff --git a/mm/vmscan.c b/mm/vmscan.c index fa08ffd04..e29b1fe67 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -57,6 +57,7 @@ #include <linux/swapops.h> #include <linux/balloon_compaction.h> #include <linux/mem_reliable.h> +#include <linux/zram_reclaim.h> #include "internal.h" @@ -2379,6 +2380,11 @@ static void get_scan_count(struct lruvec *lruvec, struct mem_cgroup *memcg, goto out; } + if (zram_reclaim_scan_balance(lruvec, memcg, &swappiness)) { + scan_balance = SCAN_ANON; + goto out; + } + /* * Prevent the reclaimer from falling into the cache trap: as * cache pages start out inactive, every cache fault will tip diff --git a/mm/workingset.c b/mm/workingset.c index a1f61b3a0..8e74fea40 100644 --- a/mm/workingset.c +++ b/mm/workingset.c @@ -15,6 +15,7 @@ #include <linux/dax.h> #include <linux/fs.h> #include <linux/mm.h> +#include <linux/zram_reclaim.h> /* * Double CLOCK lists @@ -291,6 +292,8 @@ bool workingset_refault(void *shadow) inc_lruvec_state(lruvec, WORKINGSET_REFAULT); + zram_reclaim_refault_cost(memcg, lruvec, true, 1); + if (refault_distance <= active_file) { inc_lruvec_state(lruvec, WORKINGSET_ACTIVATE); rcu_read_unlock(); -- 2.33.0
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