On Thu 13-06-13 17:12:55, Li Zefan wrote: > Sorry for updating the patchset so late. > > I've made some changes for the memory barrier thing, and I agree with > Michal that there can be improvement but can be a separate patch. > > If this version is ok for everyone, I'll send the whole patchset out > to Andrew. > > ========================= > > Use css_get/put instead of mem_cgroup_get/put. > > We can't do a simple replacement, because here mem_cgroup_put() > is called during mem_cgroup_css_free(), while mem_cgroup_css_free() > won't be called until css refcnt goes down to 0. > > Instead we increment css refcnt in mem_cgroup_css_offline(), and > then check if there's still kmem charges. If not, css refcnt will > be decremented immediately,
> otherwise the refcnt won't be decremented when kmem charges goes down > to 0. This is a bit confusing. What about "otherwise the css refcount will be released after the last kmem allocation is uncharged." > > v3: > - changed wmb() to smp_smb(), and moved it to memcg_kmem_mark_dead(), > and added comment. > > v2: > - added wmb() in kmem_cgroup_css_offline(), pointed out by Michal > - revised comments as suggested by Michal > - fixed to check if kmem is activated in kmem_cgroup_css_offline() > > Signed-off-by: Li Zefan <[email protected]> > Acked-by: Michal Hocko <[email protected]> > Acked-by: KAMEZAWA Hiroyuki <[email protected]> > --- > mm/memcontrol.c | 70 > ++++++++++++++++++++++++++++++++++++--------------------- > 1 file changed, 45 insertions(+), 25 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 466c595..76dcd0e 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -416,6 +416,11 @@ static void memcg_kmem_clear_activated(struct mem_cgroup > *memcg) > > static void memcg_kmem_mark_dead(struct mem_cgroup *memcg) > { > + /* > + * We need to call css_get() first, because memcg_uncharge_kmem() > + * will call css_put() if it sees the memcg is dead. > + */ > + smb_wmb(); > if (test_bit(KMEM_ACCOUNTED_ACTIVE, &memcg->kmem_account_flags)) > set_bit(KMEM_ACCOUNTED_DEAD, &memcg->kmem_account_flags); I do not feel strongly about that but maybe open coding this in mem_cgroup_css_offline would be even better. There is only single caller and there is smaller chance somebody will use the function incorrectly later on. So I leave the decision on you because this doesn't matter much. [...] -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
