From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id AF2CEC433F5 for ; Tue, 12 Oct 2021 10:43:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7E8A86101D for ; Tue, 12 Oct 2021 10:43:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236056AbhJLKpJ (ORCPT ); Tue, 12 Oct 2021 06:45:09 -0400 Received: from relay.sw.ru ([185.231.240.75]:44362 "EHLO relay.sw.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235900AbhJLKpH (ORCPT ); Tue, 12 Oct 2021 06:45:07 -0400 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 =; Received: from [172.29.1.17] by relay.sw.ru with esmtp (Exim 4.94.2) (envelope-from ) id 1maFFO-005nHz-Qb; Tue, 12 Oct 2021 13:43:02 +0300 Subject: Re: [PATCH memcg] mm/page_alloc.c: avoid statistic update with 0 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 References: <29155011-f884-b0e5-218e-911039568acb@suse.cz> From: Vasily Averin Message-ID: Date: Tue, 12 Oct 2021 13:42:41 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: <29155011-f884-b0e5-218e-911039568acb@suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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); >> >> >