linux-kernel - Re: [PATCH] MM: discard __GFP

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Message-id: <163727657594.13692.10357464624495712361@noble.neil.brown.name>
Date:   Fri, 19 Nov 2021 10:02:55 +1100
From:   "NeilBrown" <neilb@...e.de>
To:     "Mel Gorman" <mgorman@...hsingularity.net>
Cc:     "Michal Hocko" <mhocko@...e.com>,
        "Andrew Morton" <akpm@...ux-foundation.org>,
        "Thierry Reding" <thierry.reding@...il.com>,
        "Matthew Wilcox" <willy@...radead.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, "Mel Gorman" <mgorman@...e.de>
Subject: Re: [PATCH] MM: discard __GFP_ATOMIC

On Fri, 19 Nov 2021, Mel Gorman wrote:
> On Thu, Nov 18, 2021 at 10:22:36AM +0100, Michal Hocko wrote:
> > [Cc Mel]
> > 
> 
> I think this patch should be ok. There are few direct users of __GFP_HIGH
> and some of them are borderline silly (e.g. mm/shmem.c specifying
> __GFP_HIGH|__GFP_NOMEMALLOC) while others just look questionable (
> drivers/md/raid10.c seems to assume __GFP_HIGH guarantees allocation
> success). Xen appears to be the worst abuser of __GFP_HIGH.

That __GFP_HIGH in raid10.c is passed to mempool_alloc(), so there is no
assumption that __GFP_HIGH will provide guarantees - the mempool does
that.
The comment - which I wrote 4 years ago and don't recall at all -
suggest it was purely about performance - get error handling out of the
way quickly.  I doubt I could justify it if challenged...

Thanks,
NeilBrown


> 
> -- 
> Mel Gorman
> SUSE Labs
> 
>