From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-113.freemail.mail.aliyun.com (out30-113.freemail.mail.aliyun.com [115.124.30.113]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 94A6A3C5555 for ; Tue, 31 Mar 2026 09:24:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.113 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774949093; cv=none; b=RNoj7nfwCA4MnqdCAL2u3WlOj5Xeh3PxT8oqF0DaVV4S0N0zaOy4J4cMpPF4UY+L9kySWjMF0P1zbhSsyGEJMlE0C+oJkfrvNfSq4DPEmAfI6fvOwT2WTUZ6Z1Xdbgy3WKTcGLMTz7QDSHVU9UI0pO9dGrc24lwEQEIUUDgYyGQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774949093; c=relaxed/simple; bh=SVhJWlwhwMJ/vtCJeDLQjxWx9Nj7czdVuFG8WfKwEpQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Riyb8plsJnRu304Ofg8TNJiX17ojHkYoO4b4wDZCT30Z4F7wYlNR+18qTdI6+wE3fLEioi1Pb10Wmq84ZrKjdyroQ4YgEdHPUK/Hn7oxG8dq+Ki5qymu81PF6apLc+0R5p2B7VsmByXQ7i4zqIrWfA73bU8Xz+leUeJ6kJocu18= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=skUgykUF; arc=none smtp.client-ip=115.124.30.113 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="skUgykUF" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1774949082; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=H4lt0+h7SS3ec9sDgVEZvfQciy8Kbtp9kBHjHsNR7ik=; b=skUgykUFH9+WXWkRLGh0NbtTVQJRz8NE45RipgsYYx/OhmD6WhfJrf65uCdbs4E2VU4JGm622LOHfPJWlaJJm8D8FIdGlNozeeBQGsYrKCjT0axLbAB5j+Gx16mzSnYu09mPDWVErp78x0Ziar7zWIIBeD0wj1NanDuENQOkNbA= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R131e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033032089153;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=25;SR=0;TI=SMTPD_---0X03xUAI_1774949080; Received: from 30.74.144.129(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0X03xUAI_1774949080 cluster:ay36) by smtp.aliyun-inc.com; Tue, 31 Mar 2026 17:24:41 +0800 Message-ID: <052ae271-509c-42c3-877e-ac8822b314e5@linux.alibaba.com> Date: Tue, 31 Mar 2026 17:24:39 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 12/12] mm/vmscan: unify writeback reclaim statistic and throttling To: kasong@tencent.com, linux-mm@kvack.org Cc: Andrew Morton , Axel Rasmussen , Yuanchu Xie , Wei Xu , Johannes Weiner , David Hildenbrand , Michal Hocko , Qi Zheng , Shakeel Butt , Lorenzo Stoakes , Barry Song , David Stevens , Chen Ridong , Leno Hou , Yafang Shao , Yu Zhao , Zicheng Wang , Kalesh Singh , Suren Baghdasaryan , Chris Li , Vernon Yang , linux-kernel@vger.kernel.org, Qi Zheng References: <20260329-mglru-reclaim-v2-0-b53a3678513c@tencent.com> <20260329-mglru-reclaim-v2-12-b53a3678513c@tencent.com> From: Baolin Wang In-Reply-To: <20260329-mglru-reclaim-v2-12-b53a3678513c@tencent.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 3/29/26 3:52 AM, Kairui Song via B4 Relay wrote: > From: Kairui Song > > Currently MGLRU and non-MGLRU handle the reclaim statistic and > writeback handling very differently, especially throttling. > Basically MGLRU just ignored the throttling part. > > Let's just unify this part, use a helper to deduplicate the code > so both setups will share the same behavior. Also remove the > folio_clear_reclaim in isolate_folio which was actively invalidating > the congestion control. PG_reclaim is now handled by shrink_folio_list, > keeping it in isolate_folio is not helpful. > > Test using following reproducer using bash: > > echo "Setup a slow device using dm delay" > dd if=/dev/zero of=/var/tmp/backing bs=1M count=2048 > LOOP=$(losetup --show -f /var/tmp/backing) > mkfs.ext4 -q $LOOP > echo "0 $(blockdev --getsz $LOOP) delay $LOOP 0 0 $LOOP 0 1000" | \ > dmsetup create slow_dev > mkdir -p /mnt/slow && mount /dev/mapper/slow_dev /mnt/slow > > echo "Start writeback pressure" > sync && echo 3 > /proc/sys/vm/drop_caches > mkdir /sys/fs/cgroup/test_wb > echo 128M > /sys/fs/cgroup/test_wb/memory.max > (echo $BASHPID > /sys/fs/cgroup/test_wb/cgroup.procs && \ > dd if=/dev/zero of=/mnt/slow/testfile bs=1M count=192) > > echo "Clean up" > echo "0 $(blockdev --getsz $LOOP) error" | dmsetup load slow_dev > dmsetup resume slow_dev > umount -l /mnt/slow && sync > dmsetup remove slow_dev > > Before this commit, `dd` will get OOM killed immediately if > MGLRU is enabled. Classic LRU is fine. > > After this commit, congestion control is now effective and no more > spin on LRU or premature OOM. > > Stress test on other workloads also looking good. > > Suggested-by: Chen Ridong > Signed-off-by: Kairui Song > --- > mm/vmscan.c | 93 +++++++++++++++++++++++++++---------------------------------- > 1 file changed, 41 insertions(+), 52 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 1783da54ada1..83c8fdf8fdc4 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -1942,6 +1942,44 @@ static int current_may_throttle(void) > return !(current->flags & PF_LOCAL_THROTTLE); > } > > +static void handle_reclaim_writeback(unsigned long nr_taken, > + struct pglist_data *pgdat, > + struct scan_control *sc, > + struct reclaim_stat *stat) > +{ > + /* > + * If dirty folios are scanned that are not queued for IO, it > + * implies that flushers are not doing their job. This can > + * happen when memory pressure pushes dirty folios to the end of > + * the LRU before the dirty limits are breached and the dirty > + * data has expired. It can also happen when the proportion of > + * dirty folios grows not through writes but through memory > + * pressure reclaiming all the clean cache. And in some cases, > + * the flushers simply cannot keep up with the allocation > + * rate. Nudge the flusher threads in case they are asleep. > + */ > + if (stat->nr_unqueued_dirty == nr_taken && nr_taken) { > + wakeup_flusher_threads(WB_REASON_VMSCAN); > + /* > + * For cgroupv1 dirty throttling is achieved by waking up > + * the kernel flusher here and later waiting on folios > + * which are in writeback to finish (see shrink_folio_list()). > + * > + * Flusher may not be able to issue writeback quickly > + * enough for cgroupv1 writeback throttling to work > + * on a large system. > + */ > + if (!writeback_throttling_sane(sc)) > + reclaim_throttle(pgdat, VMSCAN_THROTTLE_WRITEBACK); > + } > + > + sc->nr.dirty += stat->nr_dirty; > + sc->nr.congested += stat->nr_congested; > + sc->nr.writeback += stat->nr_writeback; > + sc->nr.immediate += stat->nr_immediate; > + sc->nr.taken += nr_taken; > +} > + > /* > * shrink_inactive_list() is a helper for shrink_node(). It returns the number > * of reclaimed pages > @@ -2005,39 +2043,7 @@ static unsigned long shrink_inactive_list(unsigned long nr_to_scan, > lruvec_lock_irq(lruvec); > lru_note_cost_unlock_irq(lruvec, file, stat.nr_pageout, > nr_scanned - nr_reclaimed); > - > - /* > - * If dirty folios are scanned that are not queued for IO, it > - * implies that flushers are not doing their job. This can > - * happen when memory pressure pushes dirty folios to the end of > - * the LRU before the dirty limits are breached and the dirty > - * data has expired. It can also happen when the proportion of > - * dirty folios grows not through writes but through memory > - * pressure reclaiming all the clean cache. And in some cases, > - * the flushers simply cannot keep up with the allocation > - * rate. Nudge the flusher threads in case they are asleep. > - */ > - if (stat.nr_unqueued_dirty == nr_taken) { > - wakeup_flusher_threads(WB_REASON_VMSCAN); > - /* > - * For cgroupv1 dirty throttling is achieved by waking up > - * the kernel flusher here and later waiting on folios > - * which are in writeback to finish (see shrink_folio_list()). > - * > - * Flusher may not be able to issue writeback quickly > - * enough for cgroupv1 writeback throttling to work > - * on a large system. > - */ > - if (!writeback_throttling_sane(sc)) > - reclaim_throttle(pgdat, VMSCAN_THROTTLE_WRITEBACK); > - } > - > - sc->nr.dirty += stat.nr_dirty; > - sc->nr.congested += stat.nr_congested; > - sc->nr.writeback += stat.nr_writeback; > - sc->nr.immediate += stat.nr_immediate; > - sc->nr.taken += nr_taken; > - > + handle_reclaim_writeback(nr_taken, pgdat, sc, &stat); > trace_mm_vmscan_lru_shrink_inactive(pgdat->node_id, > nr_scanned, nr_reclaimed, &stat, sc->priority, file); > return nr_reclaimed; > @@ -4651,9 +4657,6 @@ static bool isolate_folio(struct lruvec *lruvec, struct folio *folio, struct sca > if (!folio_test_referenced(folio)) > set_mask_bits(&folio->flags.f, LRU_REFS_MASK, 0); > > - /* for shrink_folio_list() */ > - folio_clear_reclaim(folio); IMO, Moving this change into patch 8 would make more sense. Otherwise LGTM.