From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1792429050; b=PPtT1Fm3pgpec9Ryo4o0gDW66hOs0z2rqSsFC5YkmCtXfiRdU6tF9ZxThe+zRILWJS9B 63Zl1wELIX3Xc5HZDHHsb2Hk8tuahAWMIKzVL7mGl0/RIXZwu5AeVQdUxaxe/W6eq69Y2 qwPOPNwXoqLJGsXWl+2M94t0CtzR0pEQSnGH/r9ze8OkjYqmwVpdf3vB/5woctJ+Ej9ia tR9eP59TH/NWd8aGBnfYCkkZgwr5Lm79DjiYOXH6gBfBdpQW70aZ6/BuBE4pL6paDHMbH arX2f37f7XL1C3OpV31p1tMKr7ApK0cd/Tca7xr8XjxuXYgykd0N7lcgXQIXe4R03mg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792429050; h=Received:DKIM-Signature:Message-ID:Subject:From:To:Cc:Date: In-Reply-To:References:Autocrypt:Content-Type: Content-Transfer-Encoding:User-Agent:MIME-Version; bh=Od2rtReIL7bq8xC+py6KjgoIClum75QNK+ffkf2+KsA=; b=Lq7sZH7065FMqPeJRjC+N3KmmcgQcUlj/pejfCkmFd0Br4znpQZCdgNwCBR3gmj77Nt5 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header.b=MZlquYDI Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5A48D1F000C4; Mon, 19 Oct 2026 16:57:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792429049; bh=Od2rtReIL7bq8xC+py6KjgoIClum75QNK+ffkf2+KsA=; h=Subject:From:To:Cc:Date:In-Reply-To:References; b=MZlquYDIkzeDjF3sMmL307ehIaswqt0v2kCfhP5kHXl1xbcqJDmot/XzenURPSnc5 5jhFMHAfb3GvMsltUgarbJJu4hvq5UaTE82XJOsngwGffbnHYv2S4P0QisNH6mLSVb P/kBGorLb+t8qoM3amZzoNWPvmuKaMuYTFtyR+ovZuaZ363HyFKZUGY6mY8VvGCdn5 bjgsNqYFwR1EtmLyzutJGOwlJ+6W1WE9plpEebsR5tGYxYCz7JKkLfkym2m3fhf+SU u/in52DWhehzR2iHE7Cm/JGLSp7KQgGR/9MwZFmT+8bXXmpZVeT74uSgZ70p+AR+CQ U6PkEi6MthLKg== Message-ID: <2bee53783a2372b8dc715350b6f6d2ad5d8770ff.camel@kernel.org> Subject: Re: [PATCH v5 2/6] mm: expose WB_DONTCACHE_DIRTY in bdi debugfs stats From: Jeff Layton To: Mike Snitzer , Chuck Lever Cc: linux-nfs@vger.kernel.org, NeilBrown , Olga Kornievskaia , Dai Ngo , Tom Talpey , Christoph Hellwig , Jens Axboe , Matthew Wilcox , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org Date: Mon, 19 Oct 2026 12:57:26 -0400 In-Reply-To: <20261019150725.1507-3-snitzer@kernel.org> References: <20261019150725.1507-1-snitzer@kernel.org> <20261019150725.1507-3-snitzer@kernel.org> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 0OX6MYPtv76hka8lW4mnRmZqqx3UtfHX/hF/zH24Gj7A6sYKYLCU3YrI2Ogiu7/ksKcl7goQjpvtV YrOOI5VGLHge0awt7bhMCTM9KAfPc+xL/ZxAMVWd3NCk5SamL2cE99UWgtvNOIYU8m6EjTLhsj8sn VluJH0/RcxEeFbnSaswVChNSGa7mXJrTR22lRL6ZPjdMgS2Km90haWPRc8Wolcz07Y2se0xpGVLEQ cDEsvv5IMmeMe1/qLZ6NaVkNuL3WOXvxaVT9USW1+/SGipO2IpKJjeDZfehlB/kpfF24+RrK+seQf 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Yy9YbXtWctUz8uvDR7shsQxAhX3qO7DilMtuGo1v97I/Kx4gXQ52syh/w6EBny71CZrOgD6kJwPVV AaM1LRC28muq91WCFhs/nzHozpbzcheyGtMUI2Ao4K6mnY+3zIuXPygZMFr9KXE6fF7HzKxKuZMJO aEZCiDOq0anx6FmOzs5E6Jqdpo/mtI8beK+BE7Va6ni7YrQlnT0i3vaTVMTiCThbqsB20VrbMjlhp f8lfK1XVNbRq/R7GZ9zHESlsa35ha60yd/j3pu5hT2xyy8krV8vGhHvnJ1XRMJBAB/UYb6FyC7S+m QZIQXVeAA+smfTT0tDrisj1U5x6ZB9b3nBg65kc= Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.60.2 (3.60.2-2.fc44) X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 On Mon, 2026-10-19 at 11:07 -0400, Mike Snitzer wrote: > The per-bdi_writeback WB_DONTCACHE_DIRTY counter drives how much the > flusher writes back in response to an IOCB_DONTCACHE kick, but it is > not reported anywhere, so the DONTCACHE dirty backlog can only be > inferred from MemFree/Cached movement. >=20 > Report it as BdiDontcacheDirty in /sys/kernel/debug/bdi//stats > and as WbDontcacheDirty in the per-wb stats, next to the > Reclaimable line. Use wb_stat_sum() rather than wb_stat() to fold in > the per-cpu batches: the flusher targets the summed value and small > backlogs would otherwise read as zero. >=20 > Fixes: 88d6f128d06d ("mm: track DONTCACHE dirty pages per bdi_writeback") > Cc: Jeff Layton > Cc: Jens Axboe > Cc: Matthew Wilcox (Oracle) > Cc: linux-mm@kvack.org > Assisted-by: LLM > Signed-off-by: Mike Snitzer > --- > mm/backing-dev.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) >=20 > diff --git a/mm/backing-dev.c b/mm/backing-dev.c > index 18e999053bae..b8a2c27e07fa 100644 > --- a/mm/backing-dev.c > +++ b/mm/backing-dev.c > @@ -46,6 +46,7 @@ struct wb_stats { > unsigned long nr_dirty_time; > unsigned long nr_writeback; > unsigned long nr_reclaimable; > + unsigned long nr_dontcache_dirty; > unsigned long nr_dirtied; > unsigned long nr_written; > unsigned long dirty_thresh; > @@ -78,6 +79,12 @@ static void collect_wb_stats(struct wb_stats *stats, > =20 > stats->nr_writeback +=3D wb_stat(wb, WB_WRITEBACK); > stats->nr_reclaimable +=3D wb_stat(wb, WB_RECLAIMABLE); > + /* > + * Sum the per-cpu batches: the dontcache flusher targets this > + * counter via wb_stat_sum() and small backlogs would otherwise > + * read as zero here. > + */ > + stats->nr_dontcache_dirty +=3D wb_stat_sum(wb, WB_DONTCACHE_DIRTY); > stats->nr_dirtied +=3D wb_stat(wb, WB_DIRTIED); > stats->nr_written +=3D wb_stat(wb, WB_WRITTEN); > stats->wb_thresh +=3D wb_calc_thresh(wb, stats->dirty_thresh); > @@ -125,6 +132,7 @@ static int bdi_debug_stats_show(struct seq_file *m, v= oid *v) > seq_printf(m, > "BdiWriteback: %10lu kB\n" > "BdiReclaimable: %10lu kB\n" > + "BdiDontcacheDirty: %10lu kB\n" > "BdiDirtyThresh: %10lu kB\n" > "DirtyThresh: %10lu kB\n" > "BackgroundThresh: %10lu kB\n" > @@ -139,6 +147,7 @@ static int bdi_debug_stats_show(struct seq_file *m, v= oid *v) > "state: %10lx\n", > K(stats.nr_writeback), > K(stats.nr_reclaimable), > + K(stats.nr_dontcache_dirty), > K(stats.wb_thresh), > K(dirty_thresh), > K(background_thresh), > @@ -163,6 +172,7 @@ static void wb_stats_show(struct seq_file *m, struct = bdi_writeback *wb, > "WbCgIno: %10lu\n" > "WbWriteback: %10lu kB\n" > "WbReclaimable: %10lu kB\n" > + "WbDontcacheDirty: %10lu kB\n" > "WbDirtyThresh: %10lu kB\n" > "WbDirtied: %10lu kB\n" > "WbWritten: %10lu kB\n" > @@ -179,6 +189,7 @@ static void wb_stats_show(struct seq_file *m, struct = bdi_writeback *wb, > #endif > K(stats->nr_writeback), > K(stats->nr_reclaimable), > + K(stats->nr_dontcache_dirty), > K(stats->wb_thresh), > K(stats->nr_dirtied), > K(stats->nr_written), Since this is for debugfs, I guess we don't have to worry about ABI. Reviewed-by: Jeff Layton