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Date: Fri, 9 Jan 2009 11:51:03 +0900
From: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: nishimura@....nes.nec.co.jp, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, balbir@...ux.vnet.ibm.com,
lizf@...fujitsu.com, menage@...gle.com
Subject: Re: [RFC][PATCH 3/4] memcg: fix for mem_cgroup_hierarchical_reclaim
On Fri, 9 Jan 2009 10:08:30 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> On Thu, 8 Jan 2009 20:08:01 +0900 (JST)
> "KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com> wrote:
>
> > Daisuke Nishimura said:
> > > If root_mem has no children, last_scaned_child is set to root_mem itself.
> > > But after some children added to root_mem, mem_cgroup_get_next_node can
> > > mem_cgroup_put the root_mem although root_mem has not been mem_cgroup_get.
> > >
> > > This patch fixes this behavior by:
> > > - Set last_scanned_child to NULL if root_mem has no children or DFS search
> > > has returned to root_mem itself(root_mem is not a "child" of root_mem).
> > > Make mem_cgroup_get_first_node return root_mem in this case.
> > > There are no mem_cgroup_get/put for root_mem.
> > > - Rename mem_cgroup_get_next_node to __mem_cgroup_get_next_node, and
> > > mem_cgroup_get_first_node to mem_cgroup_get_next_node.
> > > Make mem_cgroup_hierarchical_reclaim call only new
> > > mem_cgroup_get_next_node.
> > >
> > >
> > > Signed-off-by: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
> >
> > Hmm, seems necessary fix. Then, it's better to rebase my patch on to this.
> >
> > Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> >
> > Maybe simpler one can be written but my patch remove all this out later....
> >
> How about this ? (just an exmaple and not tested, sorry)
>
>
hmm, I don't think it's much simpler than this one(I don't want last_scanned_child
to point to the mem itself, because it's not a "child").
This part will be re-written by your patch, but this patch is needed
to fix a bug(I saw general protection fault), so let's fix one by one.
I'll post my original version. It's well tested :)
Thanks,
Daisuke Nishimura.
>
> ---
> mm/memcontrol.c | 52 ++++++++++++++++++++++------------------------------
> 1 file changed, 22 insertions(+), 30 deletions(-)
>
> Index: mmotm-2.6.28-Jan7/mm/memcontrol.c
> ===================================================================
> --- mmotm-2.6.28-Jan7.orig/mm/memcontrol.c
> +++ mmotm-2.6.28-Jan7/mm/memcontrol.c
> @@ -621,6 +621,7 @@ static struct mem_cgroup *
> mem_cgroup_get_next_node(struct mem_cgroup *curr, struct mem_cgroup *root_mem)
> {
> struct cgroup *cgroup, *curr_cgroup, *root_cgroup;
> + struct mem_cgroup *orig = root_mem->last_scanned_child;
>
> curr_cgroup = curr->css.cgroup;
> root_cgroup = root_mem->css.cgroup;
> @@ -629,19 +630,15 @@ mem_cgroup_get_next_node(struct mem_cgro
> /*
> * Walk down to children
> */
> - mem_cgroup_put(curr);
> cgroup = list_entry(curr_cgroup->children.next,
> struct cgroup, sibling);
> curr = mem_cgroup_from_cont(cgroup);
> - mem_cgroup_get(curr);
> goto done;
> }
>
> visit_parent:
> if (curr_cgroup == root_cgroup) {
> - mem_cgroup_put(curr);
> curr = root_mem;
> - mem_cgroup_get(curr);
> goto done;
> }
>
> @@ -649,11 +646,9 @@ visit_parent:
> * Goto next sibling
> */
> if (curr_cgroup->sibling.next != &curr_cgroup->parent->children) {
> - mem_cgroup_put(curr);
> cgroup = list_entry(curr_cgroup->sibling.next, struct cgroup,
> sibling);
> curr = mem_cgroup_from_cont(cgroup);
> - mem_cgroup_get(curr);
> goto done;
> }
>
> @@ -664,7 +659,10 @@ visit_parent:
> goto visit_parent;
>
> done:
> + if (orig)
> + mem_cgroup_put(orig);
> root_mem->last_scanned_child = curr;
> + mem_cgroup_get(curr);
> return curr;
> }
>
> @@ -677,35 +675,25 @@ static struct mem_cgroup *
> mem_cgroup_get_first_node(struct mem_cgroup *root_mem)
> {
> struct cgroup *cgroup;
> - struct mem_cgroup *ret;
> - bool obsolete;
> + struct mem_cgroup *ret, *orig;
>
> - obsolete = mem_cgroup_is_obsolete(root_mem->last_scanned_child);
> -
> - /*
> - * Scan all children under the mem_cgroup mem
> - */
> mutex_lock(&mem_cgroup_subsys.hierarchy_mutex);
> - if (list_empty(&root_mem->css.cgroup->children)) {
> - ret = root_mem;
> - goto done;
> - }
> -
> - if (!root_mem->last_scanned_child || obsolete) {
> -
> - if (obsolete && root_mem->last_scanned_child)
> - mem_cgroup_put(root_mem->last_scanned_child);
> + orig = root_mem->last_scanned_child;
>
> - cgroup = list_first_entry(&root_mem->css.cgroup->children,
> - struct cgroup, sibling);
> - ret = mem_cgroup_from_cont(cgroup);
> + if (!orig) {
> + if (list_empty(&root_mem->css.cgroup->children)) {
> + ret = root_mem;
> + } else {
> + cgroup =
> + list_first_entry(&root_mem->css.cgroup->children,
> + struct cgroup, sibling);
> + ret = mem_cgroup_from_cont(cgroup);
> + }
> + root_mem->last_scanned_child = ret;
> mem_cgroup_get(ret);
> - } else
> + } else /* get_next_node will manage refcnt */
> ret = mem_cgroup_get_next_node(root_mem->last_scanned_child,
> root_mem);
> -
> -done:
> - root_mem->last_scanned_child = ret;
> mutex_unlock(&mem_cgroup_subsys.hierarchy_mutex);
> return ret;
> }
> @@ -2232,7 +2220,11 @@ static void mem_cgroup_pre_destroy(struc
> static void mem_cgroup_destroy(struct cgroup_subsys *ss,
> struct cgroup *cont)
> {
> - mem_cgroup_put(mem_cgroup_from_cont(cont));
> + struct mem_cgroup *mem = mem_cgroup_from_cont(cont);
> +
> + if (mem->last_scanned_child == mem)
> + mem_cgroup_put(mem);
> + mem_cgroup_put(mem);
> }
>
> static int mem_cgroup_populate(struct cgroup_subsys *ss,
>
--
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