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Mon, 14 Sep 2020 09:51:30 -0400 X-MC-Unique: FShcX2-SMQ2YvK_dh2FRxA-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 479C884F227; Mon, 14 Sep 2020 13:51:28 +0000 (UTC) Received: from llong.remote.csb (ovpn-118-85.rdu2.redhat.com [10.10.118.85]) by smtp.corp.redhat.com (Postfix) with ESMTP id A85011002D60; Mon, 14 Sep 2020 13:51:26 +0000 (UTC) Subject: Re: [PATCH v2 2/3] mm/memcg: Simplify mem_cgroup_get_max() To: Michal Hocko Cc: Johannes Weiner , Vladimir Davydov , Andrew Morton , Tejun Heo , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, Shakeel Butt , Chris Down , Roman Gushchin , Yafang Shao References: <20200914024452.19167-1-longman@redhat.com> <20200914024452.19167-3-longman@redhat.com> <20200914114825.GM16999@dhcp22.suse.cz> From: Waiman Long Organization: Red Hat Message-ID: Date: Mon, 14 Sep 2020 09:51:26 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <20200914114825.GM16999@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Rspamd-Queue-Id: 5BBB61813CBA3 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 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 9/14/20 7:48 AM, Michal Hocko wrote: > On Sun 13-09-20 22:44:51, Waiman Long wrote: >> The mem_cgroup_get_max() function used to get memory+swap max from >> both the v1 memsw and v2 memory+swap page counters & return the maximu= m >> of these 2 values. This is redundant and it is more efficient to just >> get either the v1 or the v2 values depending on which one is currently >> in use. >> >> Signed-off-by: Waiman Long >> --- >> mm/memcontrol.c | 20 +++++++++----------- >> 1 file changed, 9 insertions(+), 11 deletions(-) >> >> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >> index 8c74f1200261..ca36bed588d1 100644 >> --- a/mm/memcontrol.c >> +++ b/mm/memcontrol.c >> @@ -1633,17 +1633,15 @@ void mem_cgroup_print_oom_meminfo(struct mem_c= group *memcg) >> */ >> unsigned long mem_cgroup_get_max(struct mem_cgroup *memcg) >> { >> - unsigned long max; >> - >> - max =3D READ_ONCE(memcg->memory.max); >> - if (mem_cgroup_swappiness(memcg)) { >> - unsigned long memsw_max; >> - unsigned long swap_max; >> - >> - memsw_max =3D memcg->memsw.max; >> - swap_max =3D READ_ONCE(memcg->swap.max); >> - swap_max =3D min(swap_max, (unsigned long)total_swap_pages); >> - max =3D min(max + swap_max, memsw_max); >> + unsigned long max =3D READ_ONCE(memcg->memory.max); >> + >> + if (cgroup_subsys_on_dfl(memory_cgrp_subsys)) { >> + if (mem_cgroup_swappiness(memcg)) >> + max +=3D min(READ_ONCE(memcg->swap.max), >> + (unsigned long)total_swap_pages); >> + } else { /* v1 */ >> + if (mem_cgroup_swappiness(memcg)) >> + max =3D memcg->memsw.max; > I agree that making v1 vs. v2 distinction here makes the code more > obvious. But I do not think your code is correct for v1. In a default > state it would lead to max =3D PAGE_COUNTER_MAX which is not something > we want, right? > > instead you want > max +=3D min(READ_ONCE(memcg->memsw.max), total_swap_pages); > You are right, it is a bit tricky for v1. I will change it to =C2=A0=C2=A0=C2=A0 max +=3D min(READ_ONCE(memcg->memsw.max) - max, total= _swap_pages): Thanks, Longman