Re: [PATCH v3] vm_swappiness=0 should still try to avoid swapping anon memory

[Nico Pache <npache@redhat.com>]

On 8/10/21 5:17 PM, Shakeel Butt wrote:
> On Tue, Aug 10, 2021 at 12:24 PM Nico Pache <npache@redhat.com> wrote:
>>
>>
> [...]
>>>
>>> I'm wondering how you're getting anon scans with swappiness=0. If you
>>> look at get_scan_count(), SCAN_FRACT with swappines=0 should always
>>> result in ap = fraction[0] = 0, which never yields any anon scan
>>> targets. So I'm thinking you're running into sc->file_is_tiny
>>> situations, meaning remaining file pages alone are not enough to
>>> restore watermarks anymore. Is that possible?
>>
>> Yes DEACTIVATE_ANON is enabling the file_is_tiny case in shrink_node(). That is what im trying to prevent in the swappiness=0 case.
>>
> 
> Can you please explain how DEACTIVATE_ANON is enabling the file_is_tiny case?


You're right. Just did a second pass... I misinterpreted the assignment to
file_is_tiny. This is not the case that is causing the issue. So back to the
SCAN_FRACT case. From my testing the refaulting still seems to be causing the
issue; however, to your point in earlier discussions, if swappiness=0 then the
get_scan_count *should* be 0.
So my patch does solve the issue by preventing the shrink_list from deactivating
the anon, but it may be hiding some other issue that is the ultimate cause.

Thanks for pointing that out!
-- Nico