On 2024/5/8 20:36, David Hildenbrand wrote:
> 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.
Good point, I will inline it.
>
>> +
>> +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>
>
Thanks!
