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Wed, 16 Sep 2026 23:36:42 +0000 X-Mizu-Trace-ID: 4af75b0470ea2add X-Migadu-Flow: FLOW_OUT Date: Wed, 16 Sep 2026 16:36:41 -0700 From: Shakeel Butt To: Usama Arif Cc: Andrew Morton , jack@suse.cz, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, willy@infradead.org, david@kernel.org, hannes@cmpxchg.org, mhocko@kernel.org, roman.gushchin@linux.dev, muchun.song@linux.dev, riel@surriel.com, kernel-team@meta.com Subject: Re: [PATCH] mm: filemap: move lruvec accounting outside the xarray lock Message-ID: References: <20260916125122.2696271-1-usama.arif@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260916125122.2696271-1-usama.arif@linux.dev> X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 5E3B3180004 X-Stat-Signature: 91gwpj6wfbn34zafjzy6hjnnoycfsip8 X-Rspam-User: X-HE-Tag: 1789601804-500737 X-HE-Meta: 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 cGcwZvW2 oKwn1kkliGY0L+ciXcJC63FVQYu85S7wbxv85RPLNvEQzZrJa0/IrClQE4Peg3u3rhiaXXcMO9Is6BCNIOhUeBoRW1FJee09FW6iTugftwmxN7TWsQon88L7geLdkX8yvDA1nysRWqCenSx5NooVWNbqyz9IleUyd0JiRNRFF09Pz80HfeudYuNOL2q7LPfgqQZN9lZiFnwIH4WuXJcpMhDj7noAYCCWGwvT56+Vzdxu8WZwhyqXAxU+Shm+qN1LK85Q/oQ2GXu0siU0gXDmVsgWdbA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Sep 16, 2026 at 05:51:22AM -0700, Usama Arif wrote: > __filemap_add_folio() inserts a folio and updates mapping->nrpages > while holding mapping->i_pages.xa_lock with interrupts disabled. The > XArray insertion and nrpages update require the lock, but the lruvec > statistic updates do not. With CONFIG_MEMCG, those calls also update > per-CPU memcg and lruvec counters and notify cgroup rstat, extending the > critical section. > > Move the lruvec accounting after a successful XArray insertion and > after xas_unlock_irq(). The page-cache references pin the folio, while > the folio lock keeps folio->mapping stable and prevents removal until > accounting is complete. This moves one lruvec update for ordinary folios > and a second for PMD-mappable folios out of the serialized section. > > In a 30-second system-wide perf lock contention -ab capture on a > production host, the hottest caller-stack record attributed to > __filemap_add_folio() had 20,867 contentions and 557.930 ms total wait. > That was 14% of the 3.998 seconds of aggregate lock wait in the > capture. Moving lruvec accuting outside of critical section should > help optimize it. > > Signed-off-by: Usama Arif Reviewed-by: Shakeel Butt