Messages in this thread | | | Date | Thu, 14 Jun 2012 12:04:54 +0200 | From | Michal Hocko <> | Subject | Re: [PATCH -V9 14/15] hugetlb/cgroup: migrate hugetlb cgroup info from oldpage to new page during migration |
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On Wed 13-06-12 15:57:33, Aneesh Kumar K.V wrote: > From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> > > With HugeTLB pages, hugetlb cgroup is uncharged in compound page destructor. Since > we are holding a hugepage reference, we can be sure that old page won't > get uncharged till the last put_page(). > > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
One question below [...] > +void hugetlb_cgroup_migrate(struct page *oldhpage, struct page *newhpage) > +{ > + struct hugetlb_cgroup *h_cg; > + > + if (hugetlb_cgroup_disabled()) > + return; > + > + VM_BUG_ON(!PageHuge(oldhpage)); > + spin_lock(&hugetlb_lock); > + h_cg = hugetlb_cgroup_from_page(oldhpage); > + set_hugetlb_cgroup(oldhpage, NULL); > + cgroup_exclude_rmdir(&h_cg->css); > + > + /* move the h_cg details to new cgroup */ > + set_hugetlb_cgroup(newhpage, h_cg); > + spin_unlock(&hugetlb_lock); > + cgroup_release_and_wakeup_rmdir(&h_cg->css); > + return; > +} > +
The changelog says that the old page won't get uncharged - which means that the the cgroup cannot go away (even if we raced with the move parent, hugetlb_lock makes sure we either see old or new cgroup) so why do we need to play with css ref. counting? -- Michal Hocko SUSE Labs SUSE LINUX s.r.o. Lihovarska 1060/12 190 00 Praha 9 Czech Republic
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