On 08.05.24 11:55, Chengming Zhou wrote:
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.
Signed-off-by: Chengming Zhou <chengming.zhou@xxxxxxxxx>
---
fs/proc/base.c | 2 +-
include/linux/ksm.h | 22 +++++++++++++++++++---
include/linux/mm_types.h | 2 +-
mm/ksm.c | 11 +++++------
4 files changed, 26 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..bfc2cf756b0d 100644
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -33,16 +33,32 @@ 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 get_ksm_zero_pages(void)
+{
+ return atomic_long_read(&ksm_zero_pages);
+}
I suggest inlining that one. The naming of the function also is a bit
inconsistent staring at the others.
+
+static inline long mm_ksm_zero_pages(struct mm_struct *mm)
+{
+ return atomic_long_read(&mm->ksm_zero_pages);
+}
+
Apart from that LGTM
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
--
Cheers,
David / dhildenb
