linux-kernel - Re: [patch] mm, slab: faster active and free stats

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Date:   Wed, 9 Nov 2016 16:38:08 -0800 (PST)
From:   David Rientjes <rientjes@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
cc:     Greg Thelen <gthelen@...gle.com>,
        Aruna Ramakrishna <aruna.ramakrishna@...cle.com>,
        Christoph Lameter <cl@...ux.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [patch] mm, slab: faster active and free stats

On Tue, 8 Nov 2016, Andrew Morton wrote:

> > Reading /proc/slabinfo or monitoring slabtop(1) can become very expensive
> > if there are many slab caches and if there are very lengthy per-node
> > partial and/or free lists.
> > 
> > Commit 07a63c41fa1f ("mm/slab: improve performance of gathering slabinfo
> > stats") addressed the per-node full lists which showed a significant
> > improvement when no objects were freed.  This patch has the same
> > motivation and optimizes the remainder of the usecases where there are
> > very lengthy partial and free lists.
> > 
> > This patch maintains per-node active_slabs (full and partial) and
> > free_slabs rather than iterating the lists at runtime when reading
> > /proc/slabinfo.
> 
> Are there any nice numbers you can share?
> 

Yes, please add this to the description:


When allocating 100GB of slab from a test cache where every slab page is
on the partial list, reading /proc/slabinfo (includes all other slab
caches on the system) takes ~247ms on average with 48 samples.

As a result of this patch, the same read takes ~0.856ms on average.