linux-kernel - Re: [PATCH v2 8/8] mm: Centralize & improve oom reporting in show

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Message-ID: <Ymeh51L7XGTeCkDG@dhcp22.suse.cz>
Date:   Tue, 26 Apr 2022 09:40:23 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Kent Overstreet <kent.overstreet@...il.com>
Cc:     Roman Gushchin <roman.gushchin@...ux.dev>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, hch@....de, hannes@...xchg.org,
        akpm@...ux-foundation.org, linux-clk@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-input@...r.kernel.org,
        rostedt@...dmis.org
Subject: Re: [PATCH v2 8/8] mm: Centralize & improve oom reporting in
 show_mem.c

On Tue 26-04-22 03:26:12, Kent Overstreet wrote:
[...]
> Anyways, the reason I think this allocation is fine is it's GFP_NOWAIT and it's
> completely fine if it fails - all we lose is some diagnostics, and also it's
> released right away.

I think you are still missing the PF_MEMALLOC point. Please have a look
how this leads to no reclaim recursion so GFP_NOWAIT has no meaning when
you are allocating from PF_MEMALLOC context (which the oom killer and
any reclaim path is). Also have a look at how __gfp_pfmemalloc_flags
makes the allocation request from that context ALLOC_NO_WATERMARKS.
See?
-- 
Michal Hocko
SUSE Labs