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Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1rmeVk-00000002X1Z-05zV; Tue, 19 Mar 2024 18:48:32 +0000 Date: Tue, 19 Mar 2024 18:48:31 +0000 From: Matthew Wilcox To: Oscar Salvador Cc: Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Michal Hocko , Vlastimil Babka , Marco Elver , Andrey Konovalov , Alexander Potapenko , Tetsuo Handa Subject: Re: [PATCH v2 2/2] mm,page_owner: Fix accounting of pages when migrating Message-ID: References: <20240319183212.17156-1-osalvador@suse.de> <20240319183212.17156-3-osalvador@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240319183212.17156-3-osalvador@suse.de> X-Stat-Signature: j1hwhhnjm87wsomj5dyek1dnhjy5aaqf X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 2B018100009 X-Rspam-User: X-HE-Tag: 1710874114-959597 X-HE-Meta: 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 S7N7M15g YpeJEAA5mJQ9lQzDxM1cL3lddrGI54+LJgZeCIdj1nYFwZNIXAvRA2DP8/MmrRAvS8rcPJ93h8LKOgyPpH0d5vTjbIS1xGkK1Y8JxjAu2i5wXlyXQhHsrdq9GMzSZ19j1pLbeWtfz6pR/Sq1nQ0fDAHCP7uM9TIwnse4AF4joz8WKvRTkQOofX9RRnw== 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, Mar 19, 2024 at 07:32:12PM +0100, Oscar Salvador wrote: > Upon migration, new allocated pages are being given the handle of the old > pages. This is problematic because it means that for the stack which > allocated the old page, we will be substracting the old page + the new one > when that page is freed, creating an accounting imbalance. > > Fix this by adding a new migrate_handle in the page_owner struct, and > record the handle that allocated the new page in __folio_copy_owner(). > Upon freeing, we check whether we have a migrate_handle, and if we do, > we use migrate_handle for dec_stack_record_count(), which will > subtract those pages from its right handle. Is this the right way to fix this problem? I would have thought we'd be better off accounting this as migration freeing the old page and allocating the new page. If I understand correctly, this is the code which says "This page was last allocated by X and freed by Y", and I would think that being last freed (or allocated) by the migration code would be a very nice hint about where a problem might stem from.