linux-kernel - Re: [PATCH v2] memcg: Prevent memcg caches to be both OFF_SLAB & OBJFREELIST

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Message-ID: <CAJcbSZE+TsP4i7GisocejQMwbVYv+AH8GY1JA8+o4Zt8ropCKw@mail.gmail.com>
Date:   Mon, 7 Nov 2016 11:52:46 -0800
From:   Thomas Garnier <thgarnie@...gle.com>
To:     Christoph Lameter <cl@...ux.com>
Cc:     David Rientjes <rientjes@...gle.com>,
        Pekka Enberg <penberg@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Greg Thelen <gthelen@...gle.com>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Michal Hocko <mhocko@...nel.org>
Subject: Re: [PATCH v2] memcg: Prevent memcg caches to be both OFF_SLAB & OBJFREELIST_SLAB

On Mon, Nov 7, 2016 at 11:28 AM, Christoph Lameter <cl@...ux.com> wrote:
> On Mon, 7 Nov 2016, Thomas Garnier wrote:
>
>> I am not sure that is possible. kmem_cache_create currently check for
>> possible alias, I assume that it goes against what memcg tries to do.
>
> What does aliasing have to do with this? The aliases must have the same
> flags otherwise the caches would not have been merged.
>

I assume there might be cases where the parent cache and the new memcg
cache are compatible for merge (same flags and size). We can bypass
that by adding SLAB_NEVER_MERGE but I am not sure what is the
consequence of that.

>> Separate the changes in two patches might make sense:
>>
>>  1) Fix the original bug by masking the flags passed to create_cache
>>  2) Add flags check in kmem_cache_create.
>>
>> Does it make sense?
>
> Sure.
>

Great, I will send both patches.

>> > I also want to make sure that there are no other callers that specify
>> > extraneou flags while we are at it.
>> I will review as many as I can but we might run into surprises (quick
>> boot on defconfig didn't show anything). That's why having two
>> different patches might be useful.
>
> These surprises can be caught later ... Just make sure that the core works
> fine with this. You cannot audit all drivers.
>

Okay, I will.



-- 
Thomas