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Message-Id: <20240513-b4-ksm-counters-v2-2-f2520183a8ca@linux.dev>
Date: Mon, 13 May 2024 10:48:37 +0800
From: Chengming Zhou <chengming.zhou@...ux.dev>
To: Andrew Morton <akpm@...ux-foundation.org>,
David Hildenbrand <david@...hat.com>, Hugh Dickins <hughd@...gle.com>,
Andrea Arcangeli <aarcange@...hat.com>, Stefan Roesch <shr@...kernel.io>,
xu xin <xu.xin16@....com.cn>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
zhouchengming@...edance.com, Chengming Zhou <chengming.zhou@...ux.dev>
Subject: [PATCH v2 2/2] mm/ksm: fix ksm_zero_pages accounting
We normally ksm_zero_pages++ in ksmd when page is merged with zero page,
but ksm_zero_pages-- is done from page tables side, which can't protected
by the ksmd mutex.
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.
Fixes: e2942062e01d ("ksm: count all zero pages placed by KSM")
Fixes: 6080d19f0704 ("ksm: add ksm zero pages for each process")
Acked-by: David Hildenbrand <david@...hat.com>
Signed-off-by: Chengming Zhou <chengming.zhou@...ux.dev>
---
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(-)
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 18550c071d71..72a1acd03675 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -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);
diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index 52c63a9c5a9c..11690dacd986 100644
--- a/include/linux/ksm.h
+++ b/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))
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 24323c7d0bd4..af3a0256fa93 100644
--- a/include/linux/mm_types.h
+++ b/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 {
diff --git a/mm/ksm.c b/mm/ksm.c
index 0f9c491552ff..6f461411d070 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -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
@@ -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(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);
--
2.45.0
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