Re: slab-nomerge (was Re: [git pull] device mapper changes for 4.3)

Linus Torvalds
2015-09-04T07:01:42Z

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