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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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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.