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Date: Fri, 4 Sep 2015 00:01:41 -0700
Message-ID: <CA+55aFxOR06BiyH9nfFXzidFGr77R_BGp_xypjFQJSnv5c+_-g@mail.gmail.com>
Subject: Re: slab-nomerge (was Re: [git pull] device mapper changes for 4.3)
From: Linus Torvalds <torvalds@linux-foundation.org>
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To: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>, Dave Chinner <dchinner@redhat.com>, Mike Snitzer <snitzer@redhat.com>, Christoph Lameter <cl@linux.com>, Pekka Enberg <penberg@kernel.org>, Andrew Morton <akpm@linux-foundation.org>, David Rientjes <rientjes@google.com>, Joonsoo Kim <iamjoonsoo.kim@lge.com>, "dm-devel@redhat.com" <dm-devel@redhat.com>, Alasdair G Kergon <agk@redhat.com>, Joe Thornber <ejt@redhat.com>, Mikulas Patocka <mpatocka@redhat.com>, Vivek Goyal <vgoyal@redhat.com>, Sami Tolvanen <samitolvanen@google.com>, Viresh Kumar <viresh.kumar@linaro.org>, Heinz Mauelshagen <heinzm@redhat.com>, linux-mm <linux-mm@kvack.org>, Sergey Senozhatsky <sergey.senozhatsky@gmail.com>

On Thu, Sep 3, 2015 at 11:35 PM, Sergey Senozhatsky
<sergey.senozhatsky.work@gmail.com> wrote:
>
> Out of curiosity, I did some quite simple-minded
> "slab_nomerge = 0" vs. "slab_nomerge = 1" tests today on my old
> x86_64 box (4gigs of RAM, ext4, 4.2.0-next-20150903):

So out of interest, was this slab or slub? Also, how repeatable is
this? The memory usage between two boots tends to be rather fragile -
some of the bigger slab users are dentries and inodes, and various
filesystem scanning events will end up skewing things a _lot_.

But if it turns out that the numbers are pretty stable, and sharing
really doesn't save memory, then that is certainly a big failure. I
think Christoph did much of his work for bigger machines where one of
the SLAB issues was the NUMA overhead, and who knows - maybe it worked
well for the load and machine in question, but not necessarily
elsewhere.

Interesting.

                   Linus

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