Thanks, I also found the codes that merge slab and add alias in
kernel 3.10.0-862.el7:
kmem_cache_create()
-> kmem_cache_create_memcg()
-> __kmem_cache_alias()
{
struct kmem_cache *s;
s = find_mergeable(size, align, flags, name, ctor);
if (s) {
s->refcount++;
/*
* Adjust the object sizes so that we clear
* the complete object on kzalloc.
*/
s->object_size = max(s->object_size, (int)size);
s->inuse = max_t(int, s->inuse, ALIGN(size, sizeof(void *)));
if (sysfs_slab_alias(s, name)) {
s->refcount--;
s = NULL;
}
}
return s;
}
> -----Original Messages-----
> From: "Aurélien Cedeyn" <aurelien.cedeyn@xxxxxxxxx>
> Sent Time: 2019-01-18 07:16:22 (Friday)
> To: wuzhouhui <wuzhouhui14@xxxxxxxxxxxxxxxx>
> Cc: linux-newbie@xxxxxxxxxxxxxxx
> Subject: Re: ksm slab do not show up in /proc/slabinfo
>
> On Thu, Jan 17, 2019 at 11:18:09PM +0100, Aurélien Cedeyn wrote:
> > 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.
> >
>
> To complete my answer, you can access/view which slab are linked
> together:
> # grep ksm /proc/slabinfo
> #
> # ls /sys/kernel/slab/ -l | grep ksm
> lrwxrwxrwx 1 root root 0 janv. 18 00:11 ksm_mm_slot -> :t-0000048
> lrwxrwxrwx 1 root root 0 janv. 18 00:11 ksm_rmap_item -> :t-0000064
> lrwxrwxrwx 1 root root 0 janv. 18 00:11 ksm_stable_node -> :t-0000064
> # ls /sys/kernel/slab/ -l | grep :t-0000048
> lrwxrwxrwx 1 root root 0 janv. 18 00:13 fasync_cache -> :t-0000048
> lrwxrwxrwx 1 root root 0 janv. 18 00:13 ftrace_event_field -> :t-0000048
> lrwxrwxrwx 1 root root 0 janv. 18 00:13 ip_fib_trie -> :t-0000048
> lrwxrwxrwx 1 root root 0 janv. 18 00:13 jbd2_inode -> :t-0000048
> lrwxrwxrwx 1 root root 0 janv. 18 00:13 ksm_mm_slot -> :t-0000048
> lrwxrwxrwx 1 root root 0 janv. 18 00:13 shared_policy_node -> :t-0000048
> drwxr-xr-x 3 root root 0 janv. 18 00:13 :t-0000048
> lrwxrwxrwx 1 root root 0 janv. 18 00:13 t10_alua_lba_map_cache -> :t-0000048
> lrwxrwxrwx 1 root root 0 janv. 18 00:13 t10_alua_lu_gp_mem_cache -> :t-0000048
> # ls /sys/kernel/slab/ -l | grep :t-0000064
> lrwxrwxrwx 1 root root 0 janv. 18 00:13 anon_vma_chain -> :t-0000064
> lrwxrwxrwx 1 root root 0 janv. 18 00:13 dccp_ackvec_record -> :t-0000064
> lrwxrwxrwx 1 root root 0 janv. 18 00:13 dccp_bind_bucket -> :t-0000064
> lrwxrwxrwx 1 root root 0 janv. 18 00:13 dmaengine-unmap-2 -> :t-0000064
> lrwxrwxrwx 1 root root 0 janv. 18 00:13 ecryptfs_global_auth_tok_cache -> :t-0000064
> lrwxrwxrwx 1 root root 0 janv. 18 00:13 ecryptfs_key_sig_cache -> :t-0000064
> lrwxrwxrwx 1 root root 0 janv. 18 00:13 fanotify_perm_event_info -> :t-0000064
> lrwxrwxrwx 1 root root 0 janv. 18 00:13 fs_cache -> :t-0000064
> lrwxrwxrwx 1 root root 0 janv. 18 00:13 io -> :t-0000064
> lrwxrwxrwx 1 root root 0 janv. 18 00:13 kmalloc-64 -> :t-0000064
> lrwxrwxrwx 1 root root 0 janv. 18 00:13 ksm_rmap_item -> :t-0000064
> lrwxrwxrwx 1 root root 0 janv. 18 00:13 ksm_stable_node -> :t-0000064
> lrwxrwxrwx 1 root root 0 janv. 18 00:13 lio_dr_cache -> :t-0000064
> lrwxrwxrwx 1 root root 0 janv. 18 00:13 lio_ooo_cache -> :t-0000064
> lrwxrwxrwx 1 root root 0 janv. 18 00:13 lio_r2t_cache -> :t-0000064
> lrwxrwxrwx 1 root root 0 janv. 18 00:13 secpath_cache -> :t-0000064
> drwxr-xr-x 3 root root 0 janv. 18 00:13 :t-0000064
> lrwxrwxrwx 1 root root 0 janv. 18 00:13 task_delay_info -> :t-0000064
> lrwxrwxrwx 1 root root 0 janv. 18 00:13 tcp_bind_bucket -> :t-0000064
>
>
> --
> Aurélien
