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Fri, 21 Feb 2025 09:33:04 -0800 (PST) Date: Fri, 21 Feb 2025 12:33:03 -0500 From: Johannes Weiner To: Brendan Jackman Cc: Vlastimil Babka , Andrew Morton , Mel Gorman , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Yosry Ahmed Subject: Re: [PATCH] mm/page_alloc: Clarify some migratetype fallback code Message-ID: <20250221173303.GA1316314@cmpxchg.org> References: <20250214-clarify-steal-v1-1-79dc5adf1b79@google.com> <20250214212647.GB233399@cmpxchg.org> <764394d9-592c-4d68-8910-67362dd8810a@suse.cz> <20250218203830.GA1264207@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Queue-Id: 916DE100009 X-Rspamd-Server: rspam07 X-Stat-Signature: ijqgj1ijexrjddyjpsrfdezferf61fjy X-HE-Tag: 1740159186-758199 X-HE-Meta: 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 Ny9qN0q1 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000039, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Feb 21, 2025 at 06:24:45PM +0100, Brendan Jackman wrote: > On Tue, 18 Feb 2025 at 21:38, Johannes Weiner 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. Good job catching that. I don't think they are needed anymore after the hygiene patches. I had proposed removing them as a follow-up, but never got around to it: https://lore.kernel.org/linux-mm/20230912150320.GB3228@cmpxchg.org/ I'll send a proper patch.