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mm/ksm: fix ksm_zero_pages accounting

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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.dev
Fixes: e2942062e0 ("ksm: count all zero pages placed by KSM")
Fixes: 6080d19f07 ("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>
This commit is contained in:
Chengming Zhou 2024-05-28 13:15:22 +08:00 committed by Andrew Morton
parent 730cdc2c72
commit c2dc78b86e
4 changed files with 21 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
fs/proc/base.c
View File

@ -3214,7 +3214,7 @@ static int proc_pid_ksm_stat(struct seq_file *m, struct pid_namespace *ns,
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);

17
include/linux/ksm.h
View File

@ -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))

2
include/linux/mm_types.h
View File

@ -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 {

11
mm/ksm.c
View File

@ -296,7 +296,7 @@ static bool ksm_use_zero_pages __read_mostly;
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_struct *vma, struct page *page,
* 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
@ -3374,7 +3373,7 @@ 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 */
@ -3663,7 +3662,7 @@ 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);
@ -3672,7 +3671,7 @@ static ssize_t general_profit_show(struct kobject *kobj,
{
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);