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[213.151.95.130]) by smtp.gmail.com with ESMTPSA id x21sm1482446wmj.42.2019.10.25.00.26.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 25 Oct 2019 00:26:28 -0700 (PDT) From: Michal Hocko To: Andrew Morton , Mel Gorman , Waiman Long Cc: Johannes Weiner , Roman Gushchin , Vlastimil Babka , Konstantin Khlebnikov , Jann Horn , Song Liu , Greg Kroah-Hartman , Rafael Aquini , , LKML , Michal Hocko Subject: [PATCH 2/2] mm, vmstat: reduce zone->lock holding time by /proc/pagetypeinfo Date: Fri, 25 Oct 2019 09:26:10 +0200 Message-Id: <20191025072610.18526-3-mhocko@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20191025072610.18526-1-mhocko@kernel.org> References: <20191025072610.18526-1-mhocko@kernel.org> MIME-Version: 1.0 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: From: Michal Hocko pagetypeinfo_showfree_print is called by zone->lock held in irq mode. This is not really nice because it blocks both any interrupts on that cpu and the page allocator. On large machines this might even trigger the hard lockup detector. Considering the pagetypeinfo is a debugging tool we do not really need exact numbers here. The primary reason to look at the outuput is to see how pageblocks are spread among different migratetypes and low number of pages is much more interesting therefore putting a bound on the number of pages on the free_list sounds like a reasonable tradeoff. The new output will simply tell [...] Node 6, zone Normal, type Movable >100000 >100000 >100000 >100000 41019 31560 23996 10054 3229 983 648 instead of Node 6, zone Normal, type Movable 399568 294127 221558 102119 41019 31560 23996 10054 3229 983 648 The limit has been chosen arbitrary and it is a subject of a future change should there be a need for that. While we are at it, also drop the zone lock after each free_list iteration which will help with the IRQ and page allocator responsiveness even further as the IRQ lock held time is always bound to those 100k pages. Suggested-by: Andrew Morton Reviewed-by: Waiman Long Signed-off-by: Michal Hocko Acked-by: Vlastimil Babka Acked-by: David Hildenbrand Acked-by: Rafael Aquini Acked-by: David Rientjes --- mm/vmstat.c | 23 ++++++++++++++++++++--- 1 file changed, 20 insertions(+), 3 deletions(-) diff --git a/mm/vmstat.c b/mm/vmstat.c index 4e885ecd44d1..ddb89f4e0486 100644 --- a/mm/vmstat.c +++ b/mm/vmstat.c @@ -1383,12 +1383,29 @@ static void pagetypeinfo_showfree_print(struct seq_file *m, unsigned long freecount = 0; struct free_area *area; struct list_head *curr; + bool overflow = false; area = &(zone->free_area[order]); - list_for_each(curr, &area->free_list[mtype]) - freecount++; - seq_printf(m, "%6lu ", freecount); + list_for_each(curr, &area->free_list[mtype]) { + /* + * Cap the free_list iteration because it might + * be really large and we are under a spinlock + * so a long time spent here could trigger a + * hard lockup detector. Anyway this is a + * debugging tool so knowing there is a handful + * of pages in this order should be more than + * sufficient + */ + if (++freecount >= 100000) { + overflow = true; + break; + } + } + seq_printf(m, "%s%6lu ", overflow ? ">" : "", freecount); + spin_unlock_irq(&zone->lock); + cond_resched(); + spin_lock_irq(&zone->lock); } seq_putc(m, '\n'); }