Messages in this thread |  | | Date | Tue, 23 Jun 2009 10:23:16 +0530 | From | Balbir Singh <> | Subject | Re: Low overhead patches for the memory cgroup controller (v5) |
| |
* KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2009-06-23 09:01:16]:
> On Mon, 22 Jun 2009 15:43:43 -0700 > Andrew Morton <akpm@linux-foundation.org> wrote: > > > On Mon, 15 Jun 2009 10:09:00 +0530 > > Balbir Singh <balbir@linux.vnet.ibm.com> wrote: > > > > > > > > ... > > > > > > This patch changes the memory cgroup and removes the overhead associated > > > with accounting all pages in the root cgroup. As a side-effect, we can > > > no longer set a memory hard limit in the root cgroup. > > > > > > A new flag to track whether the page has been accounted or not > > > has been added as well. Flags are now set atomically for page_cgroup, > > > pcg_default_flags is now obsolete and removed. > > > > > > ... > > > > > > @@ -1114,9 +1121,22 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *mem, > > > css_put(&mem->css); > > > return; > > > } > > > + > > > pc->mem_cgroup = mem; > > > smp_wmb(); > > > - pc->flags = pcg_default_flags[ctype]; > > > + switch (ctype) { > > > + case MEM_CGROUP_CHARGE_TYPE_CACHE: > > > + case MEM_CGROUP_CHARGE_TYPE_SHMEM: > > > + SetPageCgroupCache(pc); > > > + SetPageCgroupUsed(pc); > > > + break; > > > + case MEM_CGROUP_CHARGE_TYPE_MAPPED: > > > + ClearPageCgroupCache(pc); > > > + SetPageCgroupUsed(pc); > > > + break; > > > + default: > > > + break; > > > + } > > > > Do we still need the smp_wmb()? > > > > It's hard to say, because we forgot to document it :( > > > Sorry for lack of documentation. > > pc->mem_cgroup should be visible before SetPageCgroupUsed(). Othrewise, > A routine believes USED bit will see bad pc->mem_cgroup. > > I'd like to add a comment later (againt new mmotm.) >
Thanks Kamezawa! We do use the barrier Andrew, an easy way to find affected code is to look at the smp_rmb()'s we have. But it is better documented.
-- Balbir
|  |