linux-kernel - Re: [PATCH mm-unstable v1] mm/page_alloc: try not to overestimate free highatomic

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Message-ID: <ZxYNLb0CiZyw31_q@tiehlicka>
Date: Mon, 21 Oct 2024 10:13:33 +0200
From: Michal Hocko <mhocko@...e.com>
To: Yu Zhao <yuzhao@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Link Lin <linkl@...gle.com>
Subject: Re: [PATCH mm-unstable v1] mm/page_alloc: try not to overestimate
 free highatomic

On Sat 19-10-24 23:13:15, Yu Zhao wrote:
> OOM kills due to vastly overestimated free highatomic reserves were
> observed:
> 
>   ... invoked oom-killer: gfp_mask=0x100cca(GFP_HIGHUSER_MOVABLE), order=0 ...
>   Node 0 Normal free:1482936kB boost:0kB min:410416kB low:739404kB high:1068392kB reserved_highatomic:1073152KB ...
>   Node 0 Normal: 1292*4kB (ME) 1920*8kB (E) 383*16kB (UE) 220*32kB (ME) 340*64kB (E) 2155*128kB (UE) 3243*256kB (UE) 615*512kB (U) 1*1024kB (M) 0*2048kB 0*4096kB = 1477408kB
> 
> The second line above shows that the OOM kill was due to the following
> condition:
> 
>   free (1482936kB) - reserved_highatomic (1073152kB) = 409784KB < min (410416kB)
> 
> And the third line shows there were no free pages in any
> MIGRATE_HIGHATOMIC pageblocks, which otherwise would show up as type
> 'H'. Therefore __zone_watermark_unusable_free() overestimated free
> highatomic reserves. IOW, it underestimated the usable free memory by
> over 1GB, which resulted in the unnecessary OOM kill.

Why doesn't unreserve_highatomic_pageblock deal with this situation?

-- 
Michal Hocko
SUSE Labs