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Sun, 13 Sep 2020 20:49:05 -0400 X-MC-Unique: gFHhDZXQMyGmwnYw-_oZFw-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 7DB18425CB; Mon, 14 Sep 2020 00:49:03 +0000 (UTC) Received: from llong.remote.csb (ovpn-113-90.rdu2.redhat.com [10.10.113.90]) by smtp.corp.redhat.com (Postfix) with ESMTP id D919F60BF3; Mon, 14 Sep 2020 00:49:01 +0000 (UTC) Subject: Re: [PATCH 2/3] mm/memcg: Simplify mem_cgroup_get_max() To: Shakeel Butt Cc: Johannes Weiner , Michal Hocko , Vladimir Davydov , Andrew Morton , Tejun Heo , LKML , Cgroups , Linux MM , Chris Down , Roman Gushchin , Yafang Shao References: <20200820130350.3211-1-longman@redhat.com> <20200820130350.3211-3-longman@redhat.com> <20200820173546.GB912520@cmpxchg.org> From: Waiman Long Organization: Red Hat Message-ID: <73bab001-b819-1e6d-e130-c52ae2206f19@redhat.com> Date: Sun, 13 Sep 2020 20:49:01 -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: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Rspamd-Queue-Id: 3D98118043DAA X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 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 8/20/20 5:25 PM, Shakeel Butt wrote: > On Thu, Aug 20, 2020 at 1:29 PM Waiman Long wrote: >> On 8/20/20 1:35 PM, Johannes Weiner wrote: >>> On Thu, Aug 20, 2020 at 09:03:49AM -0400, 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 maximum >>>> 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 | 14 +++++--------- >>>> 1 file changed, 5 insertions(+), 9 deletions(-) >>>> >>>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >>>> index 26b7a48d3afb..d219dca5239f 100644 >>>> --- a/mm/memcontrol.c >>>> +++ b/mm/memcontrol.c >>>> @@ -1633,17 +1633,13 @@ void mem_cgroup_print_oom_meminfo(struct mem_cgroup *memcg) >>>> */ >>>> unsigned long mem_cgroup_get_max(struct mem_cgroup *memcg) >>>> { >>>> - unsigned long max; >>>> + unsigned long max = READ_ONCE(memcg->memory.max); >>>> >>>> - max = READ_ONCE(memcg->memory.max); >>>> if (mem_cgroup_swappiness(memcg)) { >>>> - unsigned long memsw_max; >>>> - unsigned long swap_max; >>>> - >>>> - memsw_max = memcg->memsw.max; >>>> - swap_max = READ_ONCE(memcg->swap.max); >>>> - swap_max = min(swap_max, (unsigned long)total_swap_pages); >>>> - max = min(max + swap_max, memsw_max); >>>> + if (cgroup_subsys_on_dfl(memory_cgrp_subsys)) >>>> + max += READ_ONCE(memcg->swap.max); >>>> + else >>>> + max = memcg->memsw.max; >>> I agree with the premise of the patch, but v1 and v2 have sufficiently >>> different logic, and the way v1 overrides max from the innermost >>> branch again also doesn't help in understanding what's going on. >>> >>> Can you please split out the v1 and v2 code? >>> >>> if (cgroup_subsys_on_dfl(memory_cgrp_subsys)) { >>> max = READ_ONCE(memcg->memory.max); >>> if (mem_cgroup_swappiness(memcg)) >>> max += READ_ONCE(memcg->swap.max); >>> } else { >>> if (mem_cgroup_swappiness(memcg)) >>> max = memcg->memsw.max; >>> else >>> max = READ_ONCE(memcg->memory.max); >>> } >>> >>> It's slightly repetitive, but IMO much more readable. >>> >> Sure. That makes it even better. >> > Can you please also add in the commit message why it is ok to drop > total_swap_pages comparison from mem_cgroup_get_max()? > My bad. I accidentally skipped the total_swap_pages check. Will add it back in v2. Cheers, Longman