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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1vyXid-0000000Gxx9-2zeM; Fri, 06 Mar 2026 16:08:03 +0000 Date: Fri, 6 Mar 2026 16:08:03 +0000 From: Matthew Wilcox To: Usama Arif Cc: "David Hildenbrand (Arm)" , Andrew Morton , npache@redhat.com, ziy@nvidia.com, linux-mm@kvack.org, matthew.brost@intel.com, joshua.hahnjy@gmail.com, hannes@cmpxchg.org, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, apopple@nvidia.com, linux-kernel@vger.kernel.org, kernel-team@meta.com Subject: Re: [PATCH] mm: migrate: requeue destination folio on deferred split queue Message-ID: References: <20260306133556.2051251-1-usama.arif@linux.dev> <64051a59-680f-40ae-b291-b884aeb7c77b@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <64051a59-680f-40ae-b291-b884aeb7c77b@linux.dev> X-Rspamd-Queue-Id: 70881180014 X-Stat-Signature: 7w8tsk9gfcgcdtpyt17idfyxbb6dqarp X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1772813295-134711 X-HE-Meta: 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 QNH3+CBn ln6wZ+CF2MKfZmpjMlWoBO9NTD8zN2OGlY4FnbUeFxDmVBAbN14KV2zBlk4IJwU3HvvL+fr9OC7mah/s1KMOgAy9oGyKNp+bQcf4SlnAcdBLnY4i/BtDQ6N0yU0tiY/xXjcpXFedzrewCvO+/ZIPUgBgMOCkGfcjdVbDhkIv/TdTVCZ+oihNu5dSSMMxA7a7xfm6yGMTGLKZnqwiHLrrzcWMEGLKgQxYzaLmkS04Qr38bEXbSF7FJwxx1sYeOj2AyuDcH3G8W6b54UjZ9MH9yp0JI2L3ZP8+vPd5FY+fmLFPsLDSbUNKqN/QtgSyVebR1pNlY Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Mar 06, 2026 at 05:12:38PM +0300, Usama Arif wrote: > + /* > + * Record whether the source folio is on the deferred split queue > + * before move_to_new_folio(), which unqueues it via > + * __folio_migrate_mapping(). > + */ > + if (folio_test_large(src) && folio_test_large_rmappable(src) && > + !data_race(list_empty(&src->_deferred_list))) Why do you need data_race() here? list_empty() contains a READ_ONCE() so shouldn't be necessary? > + old_page_state |= PAGE_WAS_ON_DEFERRED_SPLIT; You've done a great job of the naming. So much so that the comment seems entirely unnecessary? > + /* > + * Requeue the destination folio on the deferred split queue if > + * the source was on the queue. The source is unqueued in > + * __folio_migrate_mapping(), so we record and check the state > + * from before move_to_new_folio(). > + */ > + if (old_page_state & PAGE_WAS_ON_DEFERRED_SPLIT) > + deferred_split_folio(dst, false); Again, I'm not sure the comment says anything that the code doesn't?