From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vasily Averin Subject: Re: [PATCH memcg] mm/page_alloc.c: avoid statistic update with 0 Date: Tue, 12 Oct 2021 13:42:41 +0300 Message-ID: References: <29155011-f884-b0e5-218e-911039568acb@suse.cz> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=virtuozzo.com; s=relay; h=Content-Type:MIME-Version:Date:Message-ID:From: Subject; bh=bEbXgNx8UNhTNiQSVrQ+7EoBtCdD7MvBGkcwxGWc4cs=; b=SmT2sdTNW0HEqxE0m moILfvR4WUkRN/qJdfdiDnBRMRXGquRZAofXgF5d54Zzkt1ln9tBN8XPALEk1iDBhHy8erFkLJ9Bo WnQyYEjYw1xSV/QWTN12zef+4kbJJVBsuatmIdz3aKFLQvIc7iGUuzKemcaf9gjg/k06zn9PtE2KM =; In-Reply-To: <29155011-f884-b0e5-218e-911039568acb@suse.cz> Content-Language: en-US List-ID: Content-Type: text/plain; charset="us-ascii" To: Vlastimil Babka , Michal Hocko Cc: Johannes Weiner , Vladimir Davydov , Andrew Morton , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel@openvz.org, Mel Gorman , Uladzislau Rezki On 08.10.2021 14:47, Vlastimil Babka wrote: > On 10/8/21 11:24, Vasily Averin wrote: >> __alloc_pages_bulk can call __count_zid_vm_events and zone_statistics >> with nr_account = 0. > > But that's not a bug, right? Just an effective no-op that's not commonly > happening, so is it worth the check? Why not? Yes, it's not a bug, it just makes the kernel a bit more efficient in a very unlikely case. However, it looks strange and makes uninformed code reviewers like me worry about possible problems inside the affected functions. No one else calls these functions from 0. >> Fixes: 3e23060b2d0b ("mm/page_alloc: batch the accounting updates in the bulk allocator") >> Signed-off-by: Vasily Averin >> --- >> mm/page_alloc.c | 7 ++++--- >> 1 file changed, 4 insertions(+), 3 deletions(-) >> >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >> index 602819a232e5..e67113452ee8 100644 >> --- a/mm/page_alloc.c >> +++ b/mm/page_alloc.c >> @@ -5364,9 +5364,10 @@ unsigned long __alloc_pages_bulk(gfp_t gfp, int preferred_nid, >> } >> >> local_unlock_irqrestore(&pagesets.lock, flags); >> - >> - __count_zid_vm_events(PGALLOC, zone_idx(zone), nr_account); >> - zone_statistics(ac.preferred_zoneref->zone, zone, nr_account); >> + if (nr_account) { >> + __count_zid_vm_events(PGALLOC, zone_idx(zone), nr_account); >> + zone_statistics(ac.preferred_zoneref->zone, zone, nr_account); >> + } >> if (objcg) >> memcg_bulk_post_charge_hook(objcg, nr_pre_charge - nr_account); >> >> >