On Thu, Jan 17, 2019 at 02:14:56PM +0800, wuzhouhui wrote:
> Hi, maybe it is a stupid question, but I just couldn't figure it out,
> since codes of ksm in 2.6.32 and 3.10.0 are similar.
>
> In CentOS 6 (kernel 2.6.32 based), I can see ksm slab from /proc/slabinfo:
> $ grep ksm /proc/slabinfo
> ksm_mm_slot 5 77 48 77 1 : tunables 120 60 8 : slabdata 1 1 0
> ksm_stable_node 414575 446016 40 92 1 : tunables 120 60 8 : slabdata 4848 4848 0
> ksm_rmap_item 43617468 43617638 64 59 1 : tunables 120 60 8 : slabdata 739282 739282 0
>
> But in CentOS 7 (kernel 3.10.0 based), they gone:
> $ sudo grep ksm /proc/slabinfo
> $
>
> Why? ksm is compiled in kernel for both centos6 and centos7.
Hi,
Maybe you should try to add this option to the kernel command line :
--------------------
slab_nomerge [MM]
Disable merging of slabs with similar size. May be
necessary if there is some reason to distinguish
allocs to different slabs, especially in hardened
environments where the risk of heap overflows and
layout control by attackers can usually be
frustrated by disabling merging. This will reduce
most of the exposure of a heap attack to a single
cache (risks via metadata attacks are mostly
unchanged). Debug options disable merging on their
own.
For more information see Documentation/vm/slub.rst.
--------------------
By default the slab are merged in CentOS 7.
I had this behaviour when switching from CentOS 6 to CentOS 7.
--
Aurélien
