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Tue, 25 Feb 2025 07:09:41 -0800 (PST) Date: Tue, 25 Feb 2025 10:09:40 -0500 From: Johannes Weiner To: Brendan Jackman Cc: Andrew Morton , Vlastimil Babka , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/3] mm: page_alloc: remove remnants of unlocked migratetype updates Message-ID: <20250225150940.GB1499716@cmpxchg.org> References: <20250225001023.1494422-1-hannes@cmpxchg.org> <20250225001023.1494422-3-hannes@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 6683C20008 X-Stat-Signature: jxkyrsy8zrrg5jdqumy14y3wzr7zan6a X-Rspam-User: X-HE-Tag: 1740496186-368884 X-HE-Meta: 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 aRIZJLPN 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, 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 Tue, Feb 25, 2025 at 01:43:35PM +0000, Brendan Jackman wrote: > On Mon, Feb 24, 2025 at 07:08:25PM -0500, Johannes Weiner wrote: > > The freelist hygiene patches made migratetype accesses fully protected > > under the zone->lock. Remove remnants of handling the race conditions > > that existed before from the MIGRATE_HIGHATOMIC code. > > > > Signed-off-by: Johannes Weiner > > Aside from my WARN bikeshedding, which isn't really about this patch > anyway: > > Reviewed-by: Brendan Jackman Thanks > > - if (is_migrate_highatomic(mt)) { > > - unsigned long size; > > - /* > > - * It should never happen but changes to > > - * locking could inadvertently allow a per-cpu > > - * drain to add pages to MIGRATE_HIGHATOMIC > > - * while unreserving so be safe and watch for > > - * underflows. > > - */ > > - size = max(pageblock_nr_pages, 1UL << order); > > - size = min(size, zone->nr_reserved_highatomic); > > - zone->nr_reserved_highatomic -= size; > > - } > > + size = max(pageblock_nr_pages, 1UL << order); > > + size = min(size, zone->nr_reserved_highatomic); > > + zone->nr_reserved_highatomic -= size; > > Now that the locking is a bit cleaner, would it make sense to add a > [VM_]WARN_ON[_ONCE] for underflow? Yeah I think that would be a nice additional cleanup. Do you want to send a patch? Otherwise, I can.