linux-kernel - Re: [PATCH] mm/slub: Detach node lock from counting free objects

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Date:   Fri, 14 Feb 2020 02:16:31 +0000 (UTC)
From:   Christopher Lameter <cl@...ux.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
cc:     Wen Yang <wenyang@...ux.alibaba.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Xunlei Pang <xlpang@...ux.alibaba.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/slub: Detach node lock from counting free objects

On Wed, 12 Feb 2020, Andrew Morton wrote:

> : reading "/proc/slabinfo" can possibly block the slab allocation on
> : another CPU for a while, 200ms in extreme cases
>
> That was bad of us.  It would be good to stop doing this.

The count is not needed for any operations. Just for the slabinfo output.
The value has no operational value for the allocator itself. So why use
extra logic to track it in potentially performance critical paths?

One could estimate the number of objects from the number of allocated
slabs instead?