Date: Wed, 9 Nov 2016 16:38:08 -0800 (PST)
From: David Rientjes <rientjes@google.com>
To: Andrew Morton <akpm@linux-foundation.org>
cc: Greg Thelen <gthelen@google.com>,
        Aruna Ramakrishna <aruna.ramakrishna@oracle.com>,
        Christoph Lameter <cl@linux.com>, Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [patch] mm, slab: faster active and free stats
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References: <alpine.DEB.2.10.1611081505240.13403@chino.kir.corp.google.com> <20161108151727.b64035da825c69bced88b46d@linux-foundation.org>
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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.