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Tue, 29 Oct 2024 08:40:21 +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 Me59A3WfIGd0DQAAD6G6ig (envelope-from ); Tue, 29 Oct 2024 08:40:21 +0000 Date: Tue, 29 Oct 2024 09:40:04 +0100 From: Oscar Salvador To: Gregory Price Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel-team@meta.com, akpm@linux-foundation.org, ying.huang@intel.com, weixugc@google.com, dave.hansen@linux.intel.com, shy828301@gmail.com, stable@vger.kernel.org Subject: Re: [PATCH] vmscan,migrate: fix double-decrement on node stats when demoting pages Message-ID: References: <20241025141724.17927-1-gourry@gourry.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241025141724.17927-1-gourry@gourry.net> X-Rspamd-Action: no action X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: E42D3180013 X-Stat-Signature: gdjzp9jk9ryihc5csrhdd8jse45it5x9 X-Rspam-User: X-HE-Tag: 1730191219-517558 X-HE-Meta: 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 Ag1wV59L ralx/60xSUl/8muoEDByaUVwFHySzo8DTCHd4gNEOvFQLFdm2tWDOWjvn4dNGqJKttfuP34AwuqTlYQBS+VhhCNNAG9sLTsdqrWqcYvve4PH39dfsScrrPXeZf86NOOaSzCUUVhT/L8dbDRtqV94+Dsc9Yg9IlrnRJ+xt2h5dXCJmxgcIyHDfNBpFprR+gxlIwCr+EC/q4R6sSDAAYxn78j2IX0kqyQWbPAOAA2dxMLwuuCyB5FDz4ddehLPtFbtHgNnHdXNzJYucKTUi0IMxFnGLoY0F58MY2QlKfBgsiTyVCW+vD926eEIQd6bPEBkAvUIwDYV6ZqG3kG8v0da417HvceCjr3HqHILI 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 Fri, Oct 25, 2024 at 10:17:24AM -0400, Gregory Price wrote: > When numa balancing is enabled with demotion, vmscan will call > migrate_pages when shrinking LRUs. Successful demotions will > cause node vmstat numbers to double-decrement, leading to an > imbalanced page count. The result is dmesg output like such: > > $ cat /proc/sys/vm/stat_refresh > > [77383.088417] vmstat_refresh: nr_isolated_anon -103212 > [77383.088417] vmstat_refresh: nr_isolated_file -899642 > > This negative value may impact compaction and reclaim throttling. > > The double-decrement occurs in the migrate_pages path: > > caller to shrink_folio_list decrements the count > shrink_folio_list > demote_folio_list > migrate_pages > migrate_pages_batch > migrate_folio_move > migrate_folio_done > mod_node_page_state(-ve) <- second decrement > > This path happens for SUCCESSFUL migrations, not failures. Typically > callers to migrate_pages are required to handle putback/accounting for > failures, but this is already handled in the shrink code. > > When accounting for migrations, instead do not decrement the count > when the migration reason is MR_DEMOTION. As of v6.11, this demotion > logic is the only source of MR_DEMOTION. > > Signed-off-by: Gregory Price > Fixes: 26aa2d199d6f2 ("mm/migrate: demote pages during reclaim") > Cc: stable@vger.kernel.org Reviewed-by: Oscar Salvador -- Oscar Salvador SUSE Labs