Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH]
 mm-vmscan-dont-mess-with-pgdat-flags-in-memcg-reclaim-v2-fix
To:     Shakeel Butt <shakeelb@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Mel Gorman <mgorman@techsingularity.net>,
        Tejun Heo <tj@kernel.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Linux MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Cgroups <cgroups@vger.kernel.org>
References: <CALvZod7P7cE38fDrWd=0caA2J6ZOmSzEuLGQH9VSaagCbo5O+A@mail.gmail.com>
 <20180406135215.10057-1-aryabinin@virtuozzo.com>
 <CALvZod7bGjx-fUKZ15oVAkXkeneZjtoRFiUSpKSZ1U0DA_e1BA@mail.gmail.com>
From:   Andrey Ryabinin <aryabinin@virtuozzo.com>
Message-ID: <406e02a5-16d4-7cd3-de01-24bee60eab02@virtuozzo.com>
Date:   Fri, 6 Apr 2018 18:09:54 +0300
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.7.0
MIME-Version: 1.0
In-Reply-To: <CALvZod7bGjx-fUKZ15oVAkXkeneZjtoRFiUSpKSZ1U0DA_e1BA@mail.gmail.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Received-SPF: None (protection.outlook.com: virtuozzo.com does not designate
 permitted sender hosts)
SpamDiagnosticOutput: 1:99
SpamDiagnosticMetadata: NSPM
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 06 Apr 2018 15:09:03.2246 (UTC)
X-MS-Exchange-CrossTenant-Network-Message-Id: ff625532-0a00-41e6-2da6-08d59bd055ed
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 0bc7f26d-0264-416e-a6fc-8352af79c58f
X-MS-Exchange-Transport-CrossTenantHeadersStamped: VI1PR08MB3264
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


On 04/06/2018 05:37 PM, Shakeel Butt wrote:

>>
>> @@ -2482,7 +2494,7 @@ static inline bool should_continue_reclaim(struct pglist_data *pgdat,
>>  static bool pgdat_memcg_congested(pg_data_t *pgdat, struct mem_cgroup *memcg)
>>  {
>>         return test_bit(PGDAT_CONGESTED, &pgdat->flags) ||
>> -               (memcg && test_memcg_bit(PGDAT_CONGESTED, memcg));
>> +               (memcg && memcg_congested(pgdat, memcg));
> 
> I am wondering if we should check all ancestors for congestion as
> well. Maybe a parallel memcg reclaimer might have set some ancestor of
> this memcg to congested.
> 

Why? If ancestor is congested but its child (the one we currently reclaim) is not,
it could mean only 2 things:
 - Either child use mostly anon and inactive file lru is small (file_lru >> priority == 0)
   so it's not congested.
 - Or the child was congested recently (at the time when ancestor scanned this group),
   but not anymore. So the information from ancestor is simply outdated.