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Thu, 21 Mar 2024 11:05:36 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id 8LM4MIAU/GUXKwAAD6G6ig (envelope-from ); Thu, 21 Mar 2024 11:05:36 +0000 Date: Thu, 21 Mar 2024 12:07:02 +0100 From: Oscar Salvador To: Vlastimil Babka Cc: Matthew Wilcox , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Michal Hocko , 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: X-Rspamd-Queue-Id: 078B4160019 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: 75fwhfkttjbntuwbrgy9onn87s31k9z9 X-HE-Tag: 1711019138-963354 X-HE-Meta: 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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 Thu, Mar 21, 2024 at 11:50:36AM +0100, Vlastimil Babka wrote: > Yeah I think we could keep that logic. I am all for keeping it. > But we could also simply subtract the refcount of the old handle (the > "allocated for migration") in __folio_copy_owner() no? Then we wouldn't need > the extra migrate_handle. Since new_page will have the old handle pointing to the old stack after the call, we could uncharge the old_page to the migrate_stack, which new_page->_handle holds before it gets changed. So we basically swap it. It could work, but I kinda have a bittersweet feeling here. I am trying to work towards to reduce the number of lookups in the hlist, but for the approach described above I would need to lookup the stack for new_page->handle in order to substract the page. OTHO, I understand that adding migrate_handle kinda wasted memory. 16MB for 16GB of memory. > Also we might have more issues here. Most page owner code takes care to set > everything for all pages within a folio, but __folio_copy_owner() and > __set_page_owner_migrate_reason() don't. I did not check deeply but do not we split the folio upon migration in case it is large? Which means we should reach split_page_owner() before the copy takes place. Do I get it right? -- Oscar Salvador SUSE Labs