linux-kernel - Re: [PATCH] mm, slub: Consider rest of partial list if acquire

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Date:   Mon, 28 Dec 2020 11:05:53 -0800 (PST)
From:   David Rientjes <rientjes@...gle.com>
To:     Jann Horn <jannh@...gle.com>
cc:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm, slub: Consider rest of partial list if acquire_slab()
 fails

On Mon, 28 Dec 2020, Jann Horn wrote:

> acquire_slab() fails if there is contention on the freelist of the page
> (probably because some other CPU is concurrently freeing an object from the
> page). In that case, it might make sense to look for a different page
> (since there might be more remote frees to the page from other CPUs, and we
> don't want contention on struct page).
> 
> However, the current code accidentally stops looking at the partial list
> completely in that case. Especially on kernels without CONFIG_NUMA set,
> this means that get_partial() fails and new_slab_objects() falls back to
> new_slab(), allocating new pages. This could lead to an unnecessary
> increase in memory fragmentation.
> 
> Fixes: 7ced37197196 ("slub: Acquire_slab() avoid loop")
> Signed-off-by: Jann Horn <jannh@...gle.com>

Acked-by: David Rientjes <rientjes@...gle.com>

Indeed, it looks like commit 7ced37197196 ("slub: Acquire_slab() avoid 
loop") stopped the iteration prematurely.