linux-kernel - Re: [PATCH] mm-vmscan-dont-mess-with-pgdat-flags-in-memcg-reclaim-v2-fix

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <406e02a5-16d4-7cd3-de01-24bee60eab02@virtuozzo.com>
Date:   Fri, 6 Apr 2018 18:09:54 +0300
From:   Andrey Ryabinin <aryabinin@...tuozzo.com>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Tejun Heo <tj@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Cgroups <cgroups@...r.kernel.org>
Subject: Re: [PATCH]
 mm-vmscan-dont-mess-with-pgdat-flags-in-memcg-reclaim-v2-fix



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 So the information from ancestor is simply outdated.