From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.223.131]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6538E19D060; Wed, 20 Nov 2024 11:57:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=195.135.223.131 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732103856; cv=none; b=DlMDrdu1B6BMsO6JPd9bu04Ec8z3+GxuwJPsaEoDl9tQy1LRlQ2pJM9C1ikYaksq4GVZmZ/cwre0IvIcUL0q5MuAfg+J/f2VeWzq/B2iUkrl3n/ewpaQadLFjVXVw6yN5ITzLgxF4IXTaRESDm2CXHtvRZiXeKJPuxjHNNziC7A= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732103856; c=relaxed/simple; bh=qKL/jn7qjS4czTVmfysiYAnNefEAEVOI9+h6G0SN/Sk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=FhZ0RvoK+eGxYpBFbwxmQOgv748Q0qLqt0RBq9PLdHKmOMwEO1uKt9OzfohaCPjC7Vv54DD9W6Db2YUTq98z29YvXugalWj16qOtLWSQzLlsi++WYflyaTe/ZsjEnMI2ne+3MOLdgWYCzvB76vJ6Ojsic4Fr7Es/t2ld2HHcwbY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz; spf=pass smtp.mailfrom=suse.cz; dkim=pass (1024-bit key) header.d=suse.cz header.i=@suse.cz header.b=qyqkFcoI; dkim=permerror (0-bit key) header.d=suse.cz header.i=@suse.cz header.b=Ddss9Gul; dkim=pass (1024-bit key) header.d=suse.cz header.i=@suse.cz header.b=qyqkFcoI; dkim=permerror (0-bit key) header.d=suse.cz header.i=@suse.cz header.b=Ddss9Gul; arc=none smtp.client-ip=195.135.223.131 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=suse.cz Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=suse.cz header.i=@suse.cz header.b="qyqkFcoI"; dkim=permerror (0-bit key) header.d=suse.cz header.i=@suse.cz header.b="Ddss9Gul"; dkim=pass (1024-bit key) header.d=suse.cz header.i=@suse.cz header.b="qyqkFcoI"; dkim=permerror (0-bit key) header.d=suse.cz header.i=@suse.cz header.b="Ddss9Gul" Received: from imap1.dmz-prg2.suse.org (imap1.dmz-prg2.suse.org [IPv6:2a07:de40:b281:104:10:150:64:97]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 613F91F76E; Wed, 20 Nov 2024 11:57:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1732103852; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=IavqSNCbqUkWJ5eYBw9gwWOmwKh1kgh1iYd5CwKJmz8=; b=qyqkFcoI32xIg3C13k1Lny8LPkxmG8CEk1duEJOZIvBXXUzHpoiLocW1IKZgCltQWTkzdD i++rtQ4R6X8CKELWPu+PvtzGi2tuHsdkNLEThjpzLF3lLKNSdahAsea6cgAE5NocnftiRo plDV9ZGQD2OHi3tC7uMNtcYPA8JFQD0= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1732103852; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=IavqSNCbqUkWJ5eYBw9gwWOmwKh1kgh1iYd5CwKJmz8=; b=Ddss9GulcQLpQgFQ7Zm0D3ki1/IrEQiCUsv0+UkWVI07Uz/cx46VoKOsra8t9iDLL6f/vx 06nNUi9PxMYdKaDA== Authentication-Results: smtp-out2.suse.de; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=qyqkFcoI; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b=Ddss9Gul DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1732103852; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=IavqSNCbqUkWJ5eYBw9gwWOmwKh1kgh1iYd5CwKJmz8=; b=qyqkFcoI32xIg3C13k1Lny8LPkxmG8CEk1duEJOZIvBXXUzHpoiLocW1IKZgCltQWTkzdD i++rtQ4R6X8CKELWPu+PvtzGi2tuHsdkNLEThjpzLF3lLKNSdahAsea6cgAE5NocnftiRo plDV9ZGQD2OHi3tC7uMNtcYPA8JFQD0= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1732103852; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=IavqSNCbqUkWJ5eYBw9gwWOmwKh1kgh1iYd5CwKJmz8=; b=Ddss9GulcQLpQgFQ7Zm0D3ki1/IrEQiCUsv0+UkWVI07Uz/cx46VoKOsra8t9iDLL6f/vx 06nNUi9PxMYdKaDA== Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id 45BDA137CF; Wed, 20 Nov 2024 11:57:32 +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 cR29EKzOPWfmAgAAD6G6ig (envelope-from ); Wed, 20 Nov 2024 11:57:32 +0000 Received: by quack3.suse.cz (Postfix, from userid 1000) id E4D17A08E1; Wed, 20 Nov 2024 12:57:31 +0100 (CET) Date: Wed, 20 Nov 2024 12:57:31 +0100 From: Jan Kara To: Jim Zhao Cc: jack@suse.cz, shikemeng@huaweicloud.com, 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: <20241120115731.gzxozbnb6eazhil7@quack3> References: <20241119114444.3925495-1-jimzhao.ai@gmail.com> <20241119122922.3939538-1-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: <20241119122922.3939538-1-jimzhao.ai@gmail.com> X-Rspamd-Queue-Id: 613F91F76E X-Spam-Level: X-Spamd-Result: default: False [-2.51 / 50.00]; BAYES_HAM(-3.00)[100.00%]; SUSPICIOUS_RECIPS(1.50)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; MID_RHS_NOT_FQDN(0.50)[]; R_DKIM_ALLOW(-0.20)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; RCVD_COUNT_THREE(0.00)[3]; MIME_TRACE(0.00)[0:+]; FREEMAIL_TO(0.00)[gmail.com]; ARC_NA(0.00)[]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; FUZZY_BLOCKED(0.00)[rspamd.com]; RCVD_TLS_LAST(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; TO_DN_SOME(0.00)[]; RCPT_COUNT_SEVEN(0.00)[8]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RECEIVED_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:106:10:150:64:167:received]; RCVD_VIA_SMTP_AUTH(0.00)[]; TAGGED_RCPT(0.00)[]; DKIM_TRACE(0.00)[suse.cz:+]; MISSING_XM_UA(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,imap1.dmz-prg2.suse.org:rdns,suse.cz:dkim] X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Rspamd-Action: no action X-Spam-Score: -2.51 X-Spam-Flag: NO Hello! On Tue 19-11-24 20:29:22, Jim Zhao wrote: > Thanks, Jan, I just sent patch v2, could you please review it ? Yes, the patch looks good to me. > > And I found the debug info in the bdi stats. > The BdiDirtyThresh value may be greater than DirtyThresh, and after > applying this patch, the value of BdiDirtyThresh could become even > larger. > > without patch: > --- > root@ubuntu:/sys/kernel/debug/bdi/8:0# cat stats > BdiWriteback: 0 kB > BdiReclaimable: 96 kB > BdiDirtyThresh: 1346824 kB But this is odd. The machine appears to have around 3GB of memory, doesn't it? I suspect this is caused by multiple cgroup-writeback contexts contributing to BdiDirtyThresh - in fact I think the math in bdi_collect_stats() is wrong as it is adding wb_thresh() calculated based on global dirty_thresh for each cgwb whereas it should be adding wb_thresh() calculated based on per-memcg dirty_thresh... You can have a look at /sys/kernel/debug/bdi/8:0/wb_stats file which should have correct limits as far as I'm reading the code. Honza > DirtyThresh: 673412 kB > BackgroundThresh: 336292 kB > BdiDirtied: 19872 kB > BdiWritten: 19776 kB > BdiWriteBandwidth: 0 kBps > b_dirty: 0 > b_io: 0 > b_more_io: 0 > b_dirty_time: 0 > bdi_list: 1 > state: 1 > > with patch: > --- > root@ubuntu:/sys/kernel/debug/bdi/8:0# cat stats > BdiWriteback: 96 kB > BdiReclaimable: 192 kB > BdiDirtyThresh: 3090736 kB > DirtyThresh: 650716 kB > BackgroundThresh: 324960 kB > BdiDirtied: 472512 kB > BdiWritten: 470592 kB > BdiWriteBandwidth: 106268 kBps > b_dirty: 2 > b_io: 0 > b_more_io: 0 > b_dirty_time: 0 > bdi_list: 1 > state: 1 > > > @kemeng, is this a normal behavior or an issue ? > > Thanks, > Jim Zhao > > > > 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. > > --- > > 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