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Thu, 21 Nov 2024 11:49:55 +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 reK2EWMeP2dJCQAAD6G6ig (envelope-from ); Thu, 21 Nov 2024 11:49:55 +0000 Received: by quack3.suse.cz (Postfix, from userid 1000) id EA8D4A089E; Thu, 21 Nov 2024 12:49:50 +0100 (CET) Date: Thu, 21 Nov 2024 12:49:50 +0100 From: Jan Kara To: Jim Zhao Cc: jack@suse.cz, akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, willy@infradead.org Subject: Re: [PATCH v2] mm/page-writeback: raise wb_thresh to prevent write blocking with strictlimit Message-ID: <20241121114950.5ie64l3lmi3dkoz5@quack3> References: <20241113100735.4jafa56p4td66z7a@quack3> <20241119114444.3925495-1-jimzhao.ai@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241119114444.3925495-1-jimzhao.ai@gmail.com> X-Spam-Level: X-Spamd-Result: default: False [-2.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; SUSPICIOUS_RECIPS(1.50)[]; NEURAL_HAM_LONG(-1.00)[-0.999]; MID_RHS_NOT_FQDN(0.50)[]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; RCVD_VIA_SMTP_AUTH(0.00)[]; TAGGED_RCPT(0.00)[]; MISSING_XM_UA(0.00)[]; FREEMAIL_TO(0.00)[gmail.com]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; RCPT_COUNT_SEVEN(0.00)[7]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; RCVD_COUNT_THREE(0.00)[3]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FUZZY_BLOCKED(0.00)[rspamd.com]; RCVD_TLS_LAST(0.00)[]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,suse.cz:email,suse.com:email] X-Spam-Score: -2.30 X-Spam-Flag: NO On Tue 19-11-24 19:44:42, Jim Zhao wrote: > With the strictlimit flag, wb_thresh acts as a hard limit in > balance_dirty_pages() and wb_position_ratio(). When device write > operations are inactive, wb_thresh can drop to 0, causing writes to be > blocked. The issue occasionally occurs in fuse fs, particularly with > network backends, the write thread is blocked frequently during a period. > To address it, this patch raises the minimum wb_thresh to a controllable > level, similar to the non-strictlimit case. > > Signed-off-by: Jim Zhao > --- > Changes in v2: > 1. Consolidate all wb_thresh bumping logic in __wb_calc_thresh for consistency; > 2. Replace the limit variable with thresh for calculating the bump value, > as __wb_calc_thresh is also used to calculate the background threshold; > 3. Add domain_dirty_avail in wb_calc_thresh to get dtc->dirty. Since the odd value of BdiDirryThresh got explained (independent cosmetic bug), feel free to add: Reviewed-by: Jan Kara Honza > --- > mm/page-writeback.c | 48 ++++++++++++++++++++++----------------------- > 1 file changed, 23 insertions(+), 25 deletions(-) > > diff --git a/mm/page-writeback.c b/mm/page-writeback.c > index e5a9eb795f99..8b13bcb42de3 100644 > --- a/mm/page-writeback.c > +++ b/mm/page-writeback.c > @@ -917,7 +917,9 @@ static unsigned long __wb_calc_thresh(struct dirty_throttle_control *dtc, > unsigned long thresh) > { > struct wb_domain *dom = dtc_dom(dtc); > + struct bdi_writeback *wb = dtc->wb; > u64 wb_thresh; > + u64 wb_max_thresh; > unsigned long numerator, denominator; > unsigned long wb_min_ratio, wb_max_ratio; > > @@ -931,11 +933,27 @@ static unsigned long __wb_calc_thresh(struct dirty_throttle_control *dtc, > wb_thresh *= numerator; > wb_thresh = div64_ul(wb_thresh, denominator); > > - wb_min_max_ratio(dtc->wb, &wb_min_ratio, &wb_max_ratio); > + wb_min_max_ratio(wb, &wb_min_ratio, &wb_max_ratio); > > wb_thresh += (thresh * wb_min_ratio) / (100 * BDI_RATIO_SCALE); > - if (wb_thresh > (thresh * wb_max_ratio) / (100 * BDI_RATIO_SCALE)) > - wb_thresh = thresh * wb_max_ratio / (100 * BDI_RATIO_SCALE); > + > + /* > + * It's very possible that wb_thresh is close to 0 not because the > + * device is slow, but that it has remained inactive for long time. > + * Honour such devices a reasonable good (hopefully IO efficient) > + * threshold, so that the occasional writes won't be blocked and active > + * writes can rampup the threshold quickly. > + */ > + if (thresh > dtc->dirty) { > + if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) > + wb_thresh = max(wb_thresh, (thresh - dtc->dirty) / 100); > + else > + wb_thresh = max(wb_thresh, (thresh - dtc->dirty) / 8); > + } > + > + wb_max_thresh = thresh * wb_max_ratio / (100 * BDI_RATIO_SCALE); > + if (wb_thresh > wb_max_thresh) > + wb_thresh = wb_max_thresh; > > return wb_thresh; > } > @@ -944,6 +962,7 @@ unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh) > { > struct dirty_throttle_control gdtc = { GDTC_INIT(wb) }; > > + domain_dirty_avail(&gdtc, true); > return __wb_calc_thresh(&gdtc, thresh); > } > > @@ -1120,12 +1139,6 @@ static void wb_position_ratio(struct dirty_throttle_control *dtc) > if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) { > long long wb_pos_ratio; > > - if (dtc->wb_dirty < 8) { > - dtc->pos_ratio = min_t(long long, pos_ratio * 2, > - 2 << RATELIMIT_CALC_SHIFT); > - return; > - } > - > if (dtc->wb_dirty >= wb_thresh) > return; > > @@ -1196,14 +1209,6 @@ static void wb_position_ratio(struct dirty_throttle_control *dtc) > */ > if (unlikely(wb_thresh > dtc->thresh)) > wb_thresh = dtc->thresh; > - /* > - * It's very possible that wb_thresh is close to 0 not because the > - * device is slow, but that it has remained inactive for long time. > - * Honour such devices a reasonable good (hopefully IO efficient) > - * threshold, so that the occasional writes won't be blocked and active > - * writes can rampup the threshold quickly. > - */ > - wb_thresh = max(wb_thresh, (limit - dtc->dirty) / 8); > /* > * scale global setpoint to wb's: > * wb_setpoint = setpoint * wb_thresh / thresh > @@ -1459,17 +1464,10 @@ static void wb_update_dirty_ratelimit(struct dirty_throttle_control *dtc, > * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate). > * Hence, to calculate "step" properly, we have to use wb_dirty as > * "dirty" and wb_setpoint as "setpoint". > - * > - * We rampup dirty_ratelimit forcibly if wb_dirty is low because > - * it's possible that wb_thresh is close to zero due to inactivity > - * of backing device. > */ > if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) { > dirty = dtc->wb_dirty; > - if (dtc->wb_dirty < 8) > - setpoint = dtc->wb_dirty + 1; > - else > - setpoint = (dtc->wb_thresh + dtc->wb_bg_thresh) / 2; > + setpoint = (dtc->wb_thresh + dtc->wb_bg_thresh) / 2; > } > > if (dirty < setpoint) { > -- > 2.20.1 > -- Jan Kara SUSE Labs, CR