Re: Regression of madvise(MADV_COLD) on shmem?

[Ivan Teterevkov <ivan.teterevkov@nutanix.com>]

On 05-Mar-22 9:49 AM, Yu Zhao wrote:
> On Sat, Mar 5, 2022 at 2:17 AM Yu Zhao <yuzhao@google.com> wrote:
>>
>> On Fri, Mar 4, 2022 at 5:18 PM Minchan Kim <minchan@kernel.org> wrote:
>>>
>>> On Fri, Mar 04, 2022 at 05:55:58PM +0000, Ivan Teterevkov wrote:
>>>> It makes me think there may be a regression in MADV_COLD. Please let me know
>>>> what do you reckon?
>>>
>>> Since deactive_page is called, I guess that's not a regression(?) from [1]
>>>
>>> Then, my random guess that you mentioned "Swap" as regression might be
>>> related to "workingset detection for anon page" since kernel changes balancing
>>> policy between file and anonymous LRU, which was merged into v5.8.
>>> It would be helpful to see if you try it on v5.7 and v5.8.
>>>
>>> [1] 12e967fd8e4e6, mm: do not allow MADV_PAGEOUT for CoW page
>>
>> Yes, I noticed this for a while. With commit b518154e59a ("mm/vmscan:
>> protect the workingset on anonymous LRU"), anon/shmem pages start on
>> the inactive lru, and in this case, deactive_page() is a NOP. Before
>> 5.9, anon/shmem pages start on the active lru, deactive_page() moves
>> zero pages in the test to the inactive lru and therefore protests the
>> "blob".
>>
>> This should fix the problem for your test case:
>>

Thank you, it does fix the test case in 5.17.0-rc6+.

>> I'll leave it to Minchan to decide whether this is worth fixing,
>> together with this one:
>>

I suppose add_page_to_lru_list_tail() makes madvise(MADV_COLD) more 
"insistent" with moving the pages at the end of the inactive LRU, but 
perhaps that's aligned with its purpose?

Cheers,
Ivan