linux-kernel - Re: [PATCH v3 1/2] memcg: Prevent memcg caches to be both OFF_SLAB & OBJFREELIST

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Date:   Mon, 7 Nov 2016 20:23:50 -0800
From:   Thomas Garnier <thgarnie@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        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 v3 1/2] memcg: Prevent memcg caches to be both OFF_SLAB & OBJFREELIST_SLAB

On Mon, Nov 7, 2016 at 2:49 PM, Andrew Morton <akpm@...ux-foundation.org> wrote:
> On Mon, 7 Nov 2016 14:32:56 -0800 Thomas Garnier <thgarnie@...gle.com> wrote:
>
>> On Mon, Nov 7, 2016 at 2:19 PM, Andrew Morton <akpm@...ux-foundation.org> wrote:
>> > On Mon,  7 Nov 2016 13:11:14 -0800 Thomas Garnier <thgarnie@...gle.com> wrote:
>> >
>> >> From: Greg Thelen <gthelen@...gle.com>
>> >>
>> >> While testing OBJFREELIST_SLAB integration with pagealloc, we found a
>> >> bug where kmem_cache(sys) would be created with both CFLGS_OFF_SLAB &
>> >> CFLGS_OBJFREELIST_SLAB.
>> >>
>> >> The original kmem_cache is created early making OFF_SLAB not possible.
>> >> When kmem_cache(sys) is created, OFF_SLAB is possible and if pagealloc
>> >> is enabled it will try to enable it first under certain conditions.
>> >> Given kmem_cache(sys) reuses the original flag, you can have both flags
>> >> at the same time resulting in allocation failures and odd behaviors.
>> >
>> > Can we please have a better description of the problems which this bug
>> > causes?  Without this info it's unclear to me which kernel version(s)
>> > need the fix.
>> >
>> > Given that the bug is 6 months old I'm assuming "not very urgent".
>> >
>>
>> I will add more details and send another round.
>
> Please simply send the additional changelog text in this thread -
> processing an entire v4 patch just for a changelog fiddle is rather
> heavyweight.
>

Got it, here is the diff of the previous commit message:

9,10c9
< CFLGS_OBJFREELIST_SLAB. When it happened, critical allocations needed
< for loading drivers or creating new caches will fail.
---
> CFLGS_OBJFREELIST_SLAB.
16c15
< at the same time.
---
> at the same time resulting in allocation failures and odd behaviors.
21,23d19
< The bug exists since 4.6-rc1 and affects testing debug pagealloc
< configurations.
<
26d21
< Signed-off-by: Thomas Garnier <thgarnie@...gle.com>

-- 
Thomas