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    SubjectRe: [PATCH next-20130703] net: sock: Add ifdef CONFIG_MEMCG_KMEM for mem_cgroup_sockets_{init,destroy}
    On Wed 03-07-13 18:11:28, Sedat Dilek wrote:
    > On Wed, Jul 3, 2013 at 5:59 PM, Michal Hocko <mhocko@suse.cz> wrote:
    > > On Wed 03-07-13 17:53:21, Sedat Dilek wrote:
    > >> On Wed, Jul 3, 2013 at 5:20 PM, Michal Hocko <mhocko@suse.cz> wrote:
    > >> > On Wed 03-07-13 20:51:00, Li Zefan wrote:
    > >> > [...]
    > >> >> [PATCH] memcg: fix build error if CONFIG_MEMCG_KMEM=n
    > >> >>
    > >> >> Fix this build error:
    > >> >>
    > >> >> mm/built-in.o: In function `mem_cgroup_css_free':
    > >> >> memcontrol.c:(.text+0x5caa6): undefined reference to
    > >> >> 'mem_cgroup_sockets_destroy'
    > >> >>
    > >> >> Reported-by: Fengguang Wu <fengguang.wu@intel.com>
    > >> >> Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
    > >> >> Signed-off-by: Li Zefan <lizefan@huawei.com>
    > >> >
    > >> > I am seeing the same thing I just didn't get to reporting it.
    > >> > The other approach is not bad as well but I find this tiny better
    > >> > because mem_cgroup_css_free should care only about a single cleanup
    > >> > function for whole kmem. If that one needs to do tcp kmem specific
    > >> > cleanup then it should be done inside kmem_cgroup_css_offline.
    > >> >
    > >>
    > >> As said in my other mail, for me this makes sense as it is a followup.
    > >>
    > >> But, still I don't know why sock.c has is own mem_cgroup_sockets_{init,destroy}.
    > >
    > > That is the only definition AFAICS (except for !CONFIG_NET where it
    > > expands to NOOP). Please note that memcg_init_kmem is a common kmem
    > > initializator and it needs to be prepared for !CONFIG_NET.
    > >
    > > The same applies to _destroy.
    > > Makes more sense now?
    > >
    >
    > So, that stuff comes originally from the net-tree.

    No, it all came from tcp kmem accounting. It is a memcg thingy and I
    guess it was placed into sock.c because it depends on some static
    symbols there (e.g. proto_list_mutex).

    > I understand the !CONFIG_NET case, but lack the understanding why
    > memcontrol.c needs _destroy.

    Because it is memcg specific and it has to be called when a group is
    destroyed.

    > Can you explain that (sorry /me is no mm-geek)?
    >
    > - Sedat -
    >
    > [1] http://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/tree/net/core/sock.c?id=next-20130703#n147
    > [2] http://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/tree/include/net/sock.h?id=next-20130703#n73
    >
    > > [...]
    > > --
    > > Michal Hocko
    > > SUSE Labs

    --
    Michal Hocko
    SUSE Labs


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