linux-kernel - Re: [PATCH] mm/page_alloc: Clarify some migratetype fallback code

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Message-ID: <CA+i-1C1m-p0GkYE8QTd39qEG3Pb_QMsEs=dLH1_87giDVhVH2A@mail.gmail.com>
Date: Fri, 21 Feb 2025 18:24:45 +0100
From: Brendan Jackman <jackmanb@...gle.com>
To: Johannes Weiner <hannes@...xchg.org>
Cc: Vlastimil Babka <vbabka@...e.cz>, Andrew Morton <akpm@...ux-foundation.org>, 
	Mel Gorman <mgorman@...hsingularity.net>, Michal Hocko <mhocko@...nel.org>, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, Yosry Ahmed <yosry.ahmed@...ux.dev>
Subject: Re: [PATCH] mm/page_alloc: Clarify some migratetype fallback code

On Tue, 18 Feb 2025 at 21:38, Johannes Weiner <hannes@...xchg.org> wrote:
>
> @@ -1930,7 +1929,7 @@ steal_suitable_fallback(struct zone *zone, struct page *page,
/*
 * This can happen due to races and we want to prevent broken
 * highatomic accounting.
 */
>         if (is_migrate_highatomic(block_type))
> -               goto single_page;
> +               return NULL;

Side question: when does this happen? Might have a spooky gap in my
understanding here as I thought the only reason the pageblock typed
was changed without the zone lock held was during memory hotplug.