linux-kernel - Re: [PATCH v7 15/17] mm: Generalize shrink_slab() calls in shrink

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Message-ID: <c9f0cf2a-5628-6d8f-662f-a381876208c1@virtuozzo.com>
Date:   Sat, 9 Jun 2018 11:46:51 +0300
From:   Kirill Tkhai <ktkhai@...tuozzo.com>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Philippe Ombredanne <pombredanne@...b.com>,
        stummala@...eaurora.org, gregkh@...uxfoundation.org,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Roman Gushchin <guro@...com>, mka@...omium.org,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Chris Wilson <chris@...is-wilson.co.uk>, longman@...hat.com,
        Minchan Kim <minchan@...nel.org>,
        Huang Ying <ying.huang@...el.com>,
        Mel Gorman <mgorman@...hsingularity.net>, jbacik@...com,
        Guenter Roeck <linux@...ck-us.net>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Matthew Wilcox <willy@...radead.org>, lirongqing@...du.com,
        Andrey Ryabinin <aryabinin@...tuozzo.com>
Subject: Re: [PATCH v7 15/17] mm: Generalize shrink_slab() calls in
 shrink_node()

Hi, Shakeel.

On 08.06.2018 22:21, Shakeel Butt wrote:
> On Tue, May 22, 2018 at 3:09 AM Kirill Tkhai <ktkhai@...tuozzo.com> wrote:
>>
>> From: Vladimir Davydov <vdavydov.dev@...il.com>
>>
>> The patch makes shrink_slab() be called for root_mem_cgroup
>> in the same way as it's called for the rest of cgroups.
>> This simplifies the logic and improves the readability.
>>
>> Signed-off-by: Vladimir Davydov <vdavydov.dev@...il.com>
>> ktkhai: Description written.
>> Signed-off-by: Kirill Tkhai <ktkhai@...tuozzo.com>
>> ---
>>  mm/vmscan.c |   21 ++++++---------------
>>  1 file changed, 6 insertions(+), 15 deletions(-)
>>
>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>> index f26ca1e00efb..6dbc659db120 100644
>> --- a/mm/vmscan.c
>> +++ b/mm/vmscan.c
>> @@ -628,10 +628,8 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
>>   * @nid is passed along to shrinkers with SHRINKER_NUMA_AWARE set,
>>   * unaware shrinkers will receive a node id of 0 instead.
>>   *
>> - * @memcg specifies the memory cgroup to target. If it is not NULL,
>> - * only shrinkers with SHRINKER_MEMCG_AWARE set will be called to scan
>> - * objects from the memory cgroup specified. Otherwise, only unaware
>> - * shrinkers are called.
>> + * @memcg specifies the memory cgroup to target. Unaware shrinkers
>> + * are called only if it is the root cgroup.
>>   *
>>   * @priority is sc->priority, we take the number of objects and >> by priority
>>   * in order to get the scan target.
>> @@ -645,7 +643,7 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
>>         struct shrinker *shrinker;
>>         unsigned long freed = 0;
>>
> 
> Shouldn't there be a VM_BUG_ON(!memcg) here?

memcg can be NULL here in case of memory controller is disabled at boot parameters
and in case of it's a global reclaim. So, such the check we can't add here.

Thanks,
Kirill