The patch titled Subject: mm/ksm: fix ksm_zero_pages accounting has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-ksm-fix-ksm_zero_pages-accounting.patch
This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...
This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days
------------------------------------------------------ From: Chengming Zhou chengming.zhou@linux.dev Subject: mm/ksm: fix ksm_zero_pages accounting Date: Tue, 28 May 2024 13:15:22 +0800
We normally ksm_zero_pages++ in ksmd when page is merged with zero page, but ksm_zero_pages-- is done from page tables side, where there is no any accessing protection of ksm_zero_pages.
So we can read very exceptional value of ksm_zero_pages in rare cases, such as -1, which is very confusing to users.
Fix it by changing to use atomic_long_t, and the same case with the mm->ksm_zero_pages.
Link: https://lkml.kernel.org/r/20240528-b4-ksm-counters-v3-2-34bb358fdc13@linux.d... Fixes: e2942062e01d ("ksm: count all zero pages placed by KSM") Fixes: 6080d19f0704 ("ksm: add ksm zero pages for each process") Signed-off-by: Chengming Zhou chengming.zhou@linux.dev Acked-by: David Hildenbrand david@redhat.com Cc: Andrea Arcangeli aarcange@redhat.com Cc: Hugh Dickins hughd@google.com Cc: Ran Xiaokai ran.xiaokai@zte.com.cn Cc: Stefan Roesch shr@devkernel.io Cc: xu xin xu.xin16@zte.com.cn Cc: Yang Yang yang.yang29@zte.com.cn Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
fs/proc/base.c | 2 +- include/linux/ksm.h | 17 ++++++++++++++--- include/linux/mm_types.h | 2 +- mm/ksm.c | 11 +++++------ 4 files changed, 21 insertions(+), 11 deletions(-)
--- a/fs/proc/base.c~mm-ksm-fix-ksm_zero_pages-accounting +++ a/fs/proc/base.c @@ -3214,7 +3214,7 @@ static int proc_pid_ksm_stat(struct seq_ mm = get_task_mm(task); if (mm) { seq_printf(m, "ksm_rmap_items %lu\n", mm->ksm_rmap_items); - seq_printf(m, "ksm_zero_pages %lu\n", mm->ksm_zero_pages); + seq_printf(m, "ksm_zero_pages %ld\n", mm_ksm_zero_pages(mm)); seq_printf(m, "ksm_merging_pages %lu\n", mm->ksm_merging_pages); seq_printf(m, "ksm_process_profit %ld\n", ksm_process_profit(mm)); mmput(mm); --- a/include/linux/ksm.h~mm-ksm-fix-ksm_zero_pages-accounting +++ a/include/linux/ksm.h @@ -33,16 +33,27 @@ void __ksm_exit(struct mm_struct *mm); */ #define is_ksm_zero_pte(pte) (is_zero_pfn(pte_pfn(pte)) && pte_dirty(pte))
-extern unsigned long ksm_zero_pages; +extern atomic_long_t ksm_zero_pages; + +static inline void ksm_map_zero_page(struct mm_struct *mm) +{ + atomic_long_inc(&ksm_zero_pages); + atomic_long_inc(&mm->ksm_zero_pages); +}
static inline void ksm_might_unmap_zero_page(struct mm_struct *mm, pte_t pte) { if (is_ksm_zero_pte(pte)) { - ksm_zero_pages--; - mm->ksm_zero_pages--; + atomic_long_dec(&ksm_zero_pages); + atomic_long_dec(&mm->ksm_zero_pages); } }
+static inline long mm_ksm_zero_pages(struct mm_struct *mm) +{ + return atomic_long_read(&mm->ksm_zero_pages); +} + static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm) { if (test_bit(MMF_VM_MERGEABLE, &oldmm->flags)) --- a/include/linux/mm_types.h~mm-ksm-fix-ksm_zero_pages-accounting +++ a/include/linux/mm_types.h @@ -985,7 +985,7 @@ struct mm_struct { * Represent how many empty pages are merged with kernel zero * pages when enabling KSM use_zero_pages. */ - unsigned long ksm_zero_pages; + atomic_long_t ksm_zero_pages; #endif /* CONFIG_KSM */ #ifdef CONFIG_LRU_GEN_WALKS_MMU struct { --- a/mm/ksm.c~mm-ksm-fix-ksm_zero_pages-accounting +++ a/mm/ksm.c @@ -296,7 +296,7 @@ static bool ksm_use_zero_pages __read_mo static bool ksm_smart_scan = true;
/* The number of zero pages which is placed by KSM */ -unsigned long ksm_zero_pages; +atomic_long_t ksm_zero_pages = ATOMIC_LONG_INIT(0);
/* The number of pages that have been skipped due to "smart scanning" */ static unsigned long ksm_pages_skipped; @@ -1429,8 +1429,7 @@ static int replace_page(struct vm_area_s * 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))); - ksm_zero_pages++; - mm->ksm_zero_pages++; + ksm_map_zero_page(mm); /* * We're replacing an anonymous page with a zero page, which is * not anonymous. We need to do proper accounting otherwise we @@ -3373,7 +3372,7 @@ static void wait_while_offlining(void) #ifdef CONFIG_PROC_FS long ksm_process_profit(struct mm_struct *mm) { - return (long)(mm->ksm_merging_pages + mm->ksm_zero_pages) * PAGE_SIZE - + return (long)(mm->ksm_merging_pages + mm_ksm_zero_pages(mm)) * PAGE_SIZE - mm->ksm_rmap_items * sizeof(struct ksm_rmap_item); } #endif /* CONFIG_PROC_FS */ @@ -3662,7 +3661,7 @@ KSM_ATTR_RO(pages_skipped); static ssize_t ksm_zero_pages_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf) { - return sysfs_emit(buf, "%ld\n", ksm_zero_pages); + return sysfs_emit(buf, "%ld\n", atomic_long_read(&ksm_zero_pages)); } KSM_ATTR_RO(ksm_zero_pages);
@@ -3671,7 +3670,7 @@ static ssize_t general_profit_show(struc { long general_profit;
- general_profit = (ksm_pages_sharing + ksm_zero_pages) * PAGE_SIZE - + general_profit = (ksm_pages_sharing + atomic_long_read(&ksm_zero_pages)) * PAGE_SIZE - ksm_rmap_items * sizeof(struct ksm_rmap_item);
return sysfs_emit(buf, "%ld\n", general_profit); _
Patches currently in -mm which might be from chengming.zhou@linux.dev are
mm-ksm-fix-ksm_pages_scanned-accounting.patch mm-ksm-fix-ksm_zero_pages-accounting.patch