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b=N1/nEJWOj9GL0Tc5obFWdlcWohS41ITXgsBTMTdVcUdZ3M00ZixvCMaMTMsT+OwuD g+ycxH/HAME4S/LIjYo4Kd1fXkJ9oXBw5XyrL07bK8TqBU9/bmJBrSqTQD+z8WMqqt 6XE1bszg5xZjnxqWX/Mj+fra/ygDz3ypMGHygi7DlO35STxFgn0c+Z7lzr5hJIFh71 MQg8Ov3kzBbxTKTQHk4DyH2htibCiDlwcpufA9EdsVjApsDhlrKxmZTukgkryU/TW0 34qnmroxipBVxkKxhm8too4dCWsX2bRYOffBv9HSWUA13VZjpGo8WJ6nzNTYAZ2D41 Xxh5crpem99iw== Date: Tue, 20 Oct 2026 18:11:53 -0400 From: Mike Snitzer To: Mike Snitzer Cc: Chuck Lever , Jeff Layton , linux-nfs@vger.kernel.org, NeilBrown , Olga Kornievskaia , Dai Ngo , Tom Talpey , Christoph Hellwig , Jens Axboe , Matthew Wilcox , Jonathan Corbet , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH v7 1/5] mm: expose WB_DONTCACHE_DIRTY in bdi debugfs stats Message-ID: References: <20261020220346.28020-1-snitzer@kernel.org> <20261020220346.28020-2-snitzer@kernel.org> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261020220346.28020-2-snitzer@kernel.org> X-Rspamd-Queue-Id: 2136D2000B X-Stat-Signature: y6sf8prhktnrw7woytkdhcnxywjarq3u X-Rspamd-Server: rspam04 X-Spam-Status: No, score=-16.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1792534315-195566 X-HE-Meta: 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 TDrK0LGb 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Tue, Oct 20, 2026 at 06:03:42PM -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. > > 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. > > Fixes: 88d6f128d06d ("mm: track DONTCACHE dirty pages per bdi_writeback") > Cc: Jeff Layton FYI, I forgot to pick up Jeff's provided review tag for this patch: Reviewed-by: Jeff Layton see: https://lore.kernel.org/linux-nfs/2bee53783a2372b8dc715350b6f6d2ad5d8770ff.camel@kernel.org/ Thanks, Mike > 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(+) > > 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, > > stats->nr_writeback += wb_stat(wb, WB_WRITEBACK); > stats->nr_reclaimable += 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 += wb_stat_sum(wb, WB_DONTCACHE_DIRTY); > stats->nr_dirtied += wb_stat(wb, WB_DIRTIED); > stats->nr_written += wb_stat(wb, WB_WRITTEN); > stats->wb_thresh += wb_calc_thresh(wb, stats->dirty_thresh); > @@ -125,6 +132,7 @@ static int bdi_debug_stats_show(struct seq_file *m, void *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, void *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), > -- > 2.52.0 >