Re: [PATCH] mm: page_io: fix psi memory pressure error on cold swapins

[Minchan Kim]

On Mon, Feb 14, 2022 at 04:49:21PM -0500, Johannes Weiner wrote:
> Once upon a time, all swapins counted toward memory pressure[1]. Then
> Joonsoo introduced workingset detection for anonymous pages and we
> gained the ability to distinguish hot from cold swapins[2][3]. But we
> failed to update swap_readpage() accordingly, and now we account
> partial memory pressure in the swapin path of cold memory.
> 
> Not for all situations - which adds more inconsistency: paths using
> the conventional submit_bio() and lock_page() route will not see much
> pressure - unless storage itself is heavily congested and the bio
> submissions stall. ZRAM and ZSWAP do most of the work directly from
> swap_readpage() and will see all swapins reflected as pressure.
> 
> Restore consistency by making all swapin stall accounting conditional
> on the page actually being part of the workingset.
> 
> [1] commit 937790699be9 ("mm/page_io.c: annotate refault stalls from swap_readpage")
> [2] commit aae466b0052e ("mm/swap: implement workingset detection for anonymous LRU")
> [3] commit cad8320b4b39 ("mm/swap: don't SetPageWorkingset unconditionally during swapin")
> 
> Reported-by: CGEL <cgel.zte@xxxxxxxxx>
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>

Acked-by: Minchan Kim <minchan@xxxxxxxxxx>