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SubjectRe: [PATCH] mm: proc: smaps_rollup: Fix pss_locked calculation
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On 1/29/19 1:15 AM, Andrew Morton wrote:
> On Sun, 20 Jan 2019 17:10:49 -0800 Sandeep Patil <sspatil@android.com> wrote:
>
>> The 'pss_locked' field of smaps_rollup was being calculated incorrectly
>> as it accumulated the current pss everytime a locked VMA was found.
>>
>> Fix that by making sure we record the current pss value before each VMA
>> is walked. So, we can only add the delta if the VMA was found to be
>> VM_LOCKED.
>>
>> ...
>>
>> --- a/fs/proc/task_mmu.c
>> +++ b/fs/proc/task_mmu.c
>> @@ -709,6 +709,7 @@ static void smap_gather_stats(struct vm_area_struct *vma,
>> #endif
>> .mm = vma->vm_mm,
>> };
>> + unsigned long pss;
>>
>> smaps_walk.private = mss;
>>
>> @@ -737,11 +738,12 @@ static void smap_gather_stats(struct vm_area_struct *vma,
>> }
>> }
>> #endif
>> -
>> + /* record current pss so we can calculate the delta after page walk */
>> + pss = mss->pss;
>> /* mmap_sem is held in m_start */
>> walk_page_vma(vma, &smaps_walk);
>> if (vma->vm_flags & VM_LOCKED)
>> - mss->pss_locked += mss->pss;
>> + mss->pss_locked += mss->pss - pss;
>> }
>
> This seems to be a rather obscure way of accumulating
> mem_size_stats.pss_locked. Wouldn't it make more sense to do this in
> smaps_account(), wherever we increment mem_size_stats.pss?
>
> It would be a tiny bit less efficient but I think that the code cleanup
> justifies such a cost?

Yeah, Sandeep could you add 'bool locked' param to smaps_account() and check it
there? We probably don't need the whole vma param yet.

Thanks.

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