From: xu xin <xu.xin16@zte.com.cn> mainline inclusion from mainline-v6.6-rc1 commit 79271476b3362a9e69adae949a520647f8af3559 category: feature bugzilla: https://atomgit.com/openeuler/kernel/issues/10169 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- Patch series "ksm: support tracking KSM-placed zero-pages", v10. The core idea of this patch set is to enable users to perceive the number of any pages merged by KSM, regardless of whether use_zero_page switch has been turned on, so that users can know how much free memory increase is really due to their madvise(MERGEABLE) actions. But the problem is, when enabling use_zero_pages, all empty pages will be merged with kernel zero pages instead of with each other as use_zero_pages is disabled, and then these zero-pages are no longer monitored by KSM. The motivations to do this is seen at: https://lore.kernel.org/lkml/202302100915227721315@zte.com.cn/ In one word, we hope to implement the support for KSM-placed zero pages tracking without affecting the feature of use_zero_pages, so that app developer can also benefit from knowing the actual KSM profit by getting KSM-placed zero pages to optimize applications eventually when /sys/kernel/mm/ksm/use_zero_pages is enabled. This patch (of 5): When use_zero_pages of ksm is enabled, madvise(addr, len, MADV_UNMERGEABLE) and other ways (like write 2 to /sys/kernel/mm/ksm/run) to trigger unsharing will *not* actually unshare the shared zeropage as placed by KSM (which is against the MADV_UNMERGEABLE documentation). As these KSM-placed zero pages are out of the control of KSM, the related counts of ksm pages don't expose how many zero pages are placed by KSM (these special zero pages are different from those initially mapped zero pages, because the zero pages mapped to MADV_UNMERGEABLE areas are expected to be a complete and unshared page). To not blindly unshare all shared zero_pages in applicable VMAs, the patch use pte_mkdirty (related with architecture) to mark KSM-placed zero pages. Thus, MADV_UNMERGEABLE will only unshare those KSM-placed zero pages. In addition, we'll reuse this mechanism to reliably identify KSM-placed ZeroPages to properly account for them (e.g., calculating the KSM profit that includes zeropages) in the latter patches. The patch will not degrade the performance of use_zero_pages as it doesn't change the way of merging empty pages in use_zero_pages's feature. Link: https://lkml.kernel.org/r/202306131104554703428@zte.com.cn Link: https://lkml.kernel.org/r/20230613030928.185882-1-yang.yang29@zte.com.cn Signed-off-by: xu xin <xu.xin16@zte.com.cn> Acked-by: David Hildenbrand <david@redhat.com> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> Cc: Xuexin Jiang <jiang.xuexin@zte.com.cn> Reviewed-by: Xiaokai Ran <ran.xiaokai@zte.com.cn> Reviewed-by: Yang Yang <yang.yang29@zte.com.cn> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Conflicts: mm/ksm.c Signed-off-by: Jinjiang Tu <tujinjiang@huawei.com> --- include/linux/ksm.h | 6 ++++++ mm/ksm.c | 31 ++++++++++++++++++++++++++++--- 2 files changed, 34 insertions(+), 3 deletions(-) diff --git a/include/linux/ksm.h b/include/linux/ksm.h index 286944d61a4a..63cd98cd75bf 100644 --- a/include/linux/ksm.h +++ b/include/linux/ksm.h @@ -28,6 +28,12 @@ int ksm_disable_merge_any(struct mm_struct *mm); int __ksm_enter(struct mm_struct *mm); void __ksm_exit(struct mm_struct *mm); +/* + * To identify zeropages that were mapped by KSM, we reuse the dirty bit + * in the PTE. If the PTE is dirty, the zeropage was mapped by KSM when + * deduplicating memory. + */ +#define is_ksm_zero_pte(pte) (is_zero_pfn(pte_pfn(pte)) && pte_dirty(pte)) static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm) { diff --git a/mm/ksm.c b/mm/ksm.c index d77fa56ec369..63b3b0b23e78 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -454,6 +454,27 @@ static inline bool ksm_test_exit(struct mm_struct *mm) return atomic_read(&mm->mm_users) == 0; } +static inline bool is_ksm_zero_page(struct mm_struct *mm, struct page *page, + unsigned long addr) +{ + pmd_t *pmd; + pte_t *ptep; + spinlock_t *ptl; + bool is_dirty; + + if (!is_zero_pfn(page_to_pfn(page))) + return false; + + pmd = mm_find_pmd(mm, addr); + if (!pmd) + return false; + + ptep = pte_offset_map_lock(mm, pmd, addr, &ptl); + is_dirty = !!pte_dirty(*ptep); + pte_unmap_unlock(ptep, ptl); + return is_dirty; +} + /* * We use break_ksm to break COW on a ksm page: it's a stripped down * @@ -480,7 +501,7 @@ static int break_ksm(struct vm_area_struct *vma, unsigned long addr) FOLL_GET | FOLL_MIGRATION | FOLL_REMOTE); if (IS_ERR_OR_NULL(page)) break; - if (PageKsm(page)) + if (PageKsm(page) || is_ksm_zero_page(vma->vm_mm, page, addr)) ret = handle_mm_fault(vma, addr, FAULT_FLAG_WRITE | FAULT_FLAG_REMOTE); else @@ -1208,8 +1229,12 @@ static int replace_page(struct vm_area_struct *vma, struct page *page, page_add_anon_rmap(kpage, vma, addr, false); newpte = mk_pte(kpage, vma->vm_page_prot); } else { - newpte = pte_mkspecial(pfn_pte(page_to_pfn(kpage), - vma->vm_page_prot)); + /* + * Use pte_mkdirty to mark the zero page mapped by KSM, and then + * we can easily track all KSM-placed zero pages by checking if + * the dirty bit in zero page's PTE is set. + */ + newpte = pte_mkdirty(pte_mkspecial(pfn_pte(page_to_pfn(kpage), vma->vm_page_prot))); /* * We're replacing an anonymous page with a zero page, which is * not anonymous. We need to do proper accounting otherwise we -- 2.43.0