From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vlastimil Babka Subject: Re: [RFC PATCH 2/2] mm, vmstat: reduce zone->lock holding time by /proc/pagetypeinfo Date: Wed, 23 Oct 2019 18:15:56 +0200 Message-ID: References: <20191023095607.GE3016@techsingularity.net> <20191023102737.32274-1-mhocko@kernel.org> <20191023102737.32274-3-mhocko@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20191023102737.32274-3-mhocko@kernel.org> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Michal Hocko , Andrew Morton , Mel Gorman , Waiman Long Cc: Johannes Weiner , Roman Gushchin , Konstantin Khlebnikov , Jann Horn , Song Liu , Greg Kroah-Hartman , Rafael Aquini , linux-mm@kvack.org, LKML , Michal Hocko , Linux API List-Id: linux-api@vger.kernel.org + linux-api On 10/23/19 12:27 PM, Michal Hocko wrote: > 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 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. > > Suggested-by: Andrew Morton > Signed-off-by: Michal Hocko > --- > mm/vmstat.c | 19 ++++++++++++++++++- > 1 file changed, 18 insertions(+), 1 deletion(-) > > diff --git a/mm/vmstat.c b/mm/vmstat.c > index 4e885ecd44d1..762034fc3b83 100644 > --- a/mm/vmstat.c > +++ b/mm/vmstat.c > @@ -1386,8 +1386,25 @@ static void pagetypeinfo_showfree_print(struct seq_file *m, > > area = &(zone->free_area[order]); > > - list_for_each(curr, &area->free_list[mtype]) > + list_for_each(curr, &area->free_list[mtype]) { > freecount++; > + /* > + * 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) { > + seq_printf(m, ">%6lu ", freecount); > + spin_unlock_irq(&zone->lock); > + cond_resched(); > + spin_lock_irq(&zone->lock); > + continue; > + } > + } > seq_printf(m, "%6lu ", freecount); > } > seq_putc(m, '\n'); >