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 14:19:19 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Thomas Garnier <thgarnie@...gle.com>
Cc:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, gthelen@...gle.com,
        vdavydov.dev@...il.com, mhocko@...nel.org
Subject: Re: [PATCH v3 1/2] memcg: Prevent memcg caches to be both OFF_SLAB
 & OBJFREELIST_SLAB

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".

> This fix discards allocator specific flags from memcg before calling
> create_cache.
> 
> Fixes: b03a017bebc4 ("mm/slab: introduce new slab management type, OBJFREELIST_SLAB")
> Signed-off-by: Greg Thelen <gthelen@...gle.com>
> Tested-by: Thomas Garnier <thgarnie@...gle.com>

This should have had your signed-off-by, as you were on the delivery
path.  I've made that change.