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Wed, 23 Oct 2019 16:21:12 +0000 (UTC) Received: from llong.remote.csb (dhcp-17-59.bos.redhat.com [10.18.17.59]) by smtp.corp.redhat.com (Postfix) with ESMTP id 5555060126; Wed, 23 Oct 2019 16:21:06 +0000 (UTC) Subject: Re: [RFC PATCH 2/2] mm, vmstat: reduce zone->lock holding time by /proc/pagetypeinfo From: Waiman Long To: Michal Hocko Cc: Andrew Morton , Mel Gorman , Johannes Weiner , Roman Gushchin , Vlastimil Babka , Konstantin Khlebnikov , Jann Horn , Song Liu , Greg Kroah-Hartman , Rafael Aquini , linux-mm@kvack.org, LKML References: <20191023095607.GE3016@techsingularity.net> <20191023102737.32274-1-mhocko@kernel.org> <20191023102737.32274-3-mhocko@kernel.org> <20191023161029.GK17610@dhcp22.suse.cz> <27e2a26d-8c9b-fdb9-782f-8efa678352b3@redhat.com> Organization: Red Hat Message-ID: <015ef5b2-7e11-02a5-6cf3-2e45f6657910@redhat.com> Date: Wed, 23 Oct 2019 12:21:05 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <27e2a26d-8c9b-fdb9-782f-8efa678352b3@redhat.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-MC-Unique: FsNnKaJeOJa4ZPGFg-Gqxg-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable 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: On 10/23/19 12:17 PM, Waiman Long wrote: > On 10/23/19 12:10 PM, Michal Hocko wrote: >> On Wed 23-10-19 10:56:30, Waiman Long wrote: >>> On 10/23/19 6:27 AM, 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 se= e >>>> how pageblocks are spread among different migratetypes therefore putti= ng >>>> a bound on the number of pages on the free_list sounds like a reasonab= le >>>> tradeoff. >>>> >>>> The new output will simply tell >>>> [...] >>>> Node 6, zone Normal, type Movable >100000 >100000 >100000 >1= 00000 41019 31560 23996 10054 3229 983 648 >>>> >>>> instead of >>>> Node 6, zone Normal, type Movable 399568 294127 221558 10211= 9 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, >>>> =20 >>>> =09=09=09area =3D &(zone->free_area[order]); >>>> =20 >>>> -=09=09=09list_for_each(curr, &area->free_list[mtype]) >>>> +=09=09=09list_for_each(curr, &area->free_list[mtype]) { >>>> =09=09=09=09freecount++; >>>> +=09=09=09=09/* >>>> +=09=09=09=09 * Cap the free_list iteration because it might >>>> +=09=09=09=09 * be really large and we are under a spinlock >>>> +=09=09=09=09 * so a long time spent here could trigger a >>>> +=09=09=09=09 * hard lockup detector. Anyway this is a >>>> +=09=09=09=09 * debugging tool so knowing there is a handful >>>> +=09=09=09=09 * of pages in this order should be more than >>>> +=09=09=09=09 * sufficient >>>> +=09=09=09=09 */ >>>> +=09=09=09=09if (freecount > 100000) { >>>> +=09=09=09=09=09seq_printf(m, ">%6lu ", freecount); >>>> +=09=09=09=09=09spin_unlock_irq(&zone->lock); >>>> +=09=09=09=09=09cond_resched(); >>>> +=09=09=09=09=09spin_lock_irq(&zone->lock); >>>> +=09=09=09=09=09continue; >>> list_for_each() is a for loop. The continue statement will just iterate >>> the rests with the possibility that curr will be stale. Should we use >>> goto to jump after the seq_print() below? >> You are right. Kinda brown paper back material. Sorry about that. What >> about this on top? >> ---=20 >> diff --git a/mm/vmstat.c b/mm/vmstat.c >> index 762034fc3b83..c156ce24a322 100644 >> --- a/mm/vmstat.c >> +++ b/mm/vmstat.c >> @@ -1383,11 +1383,11 @@ static void pagetypeinfo_showfree_print(struct s= eq_file *m, >> =09=09=09unsigned long freecount =3D 0; >> =09=09=09struct free_area *area; >> =09=09=09struct list_head *curr; >> +=09=09=09bool overflow =3D false; >> =20 >> =09=09=09area =3D &(zone->free_area[order]); >> =20 >> =09=09=09list_for_each(curr, &area->free_list[mtype]) { >> -=09=09=09=09freecount++; >> =09=09=09=09/* >> =09=09=09=09 * Cap the free_list iteration because it might >> =09=09=09=09 * be really large and we are under a spinlock >> @@ -1397,15 +1397,15 @@ static void pagetypeinfo_showfree_print(struct s= eq_file *m, >> =09=09=09=09 * of pages in this order should be more than >> =09=09=09=09 * sufficient >> =09=09=09=09 */ >> -=09=09=09=09if (freecount > 100000) { >> -=09=09=09=09=09seq_printf(m, ">%6lu ", freecount); >> +=09=09=09=09if (++freecount >=3D 100000) { >> +=09=09=09=09=09overflow =3D true; >> =09=09=09=09=09spin_unlock_irq(&zone->lock); >> =09=09=09=09=09cond_resched(); >> =09=09=09=09=09spin_lock_irq(&zone->lock); >> -=09=09=09=09=09continue; >> +=09=09=09=09=09break; >> =09=09=09=09} >> =09=09=09} >> -=09=09=09seq_printf(m, "%6lu ", freecount); >> +=09=09=09seq_printf(m, "%s%6lu ", overflow ? ">" : "", freecount); >> =09=09} >> =09=09seq_putc(m, '\n'); >> =09} >> > Yes, that looks good to me. There is still a small chance that the > description will be a bit off if it is exactly 100,000. However, it is > not a big deal and I can live with that. Alternatively, you can do if (++freecount > 100000) { =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 : =C2=A0=C2=A0=C2=A0 freecount--; =C2=A0=C2=A0=C2=A0 break; } Cheers, Longman