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Date: Tue, 25 Nov 2008 20:58:32 +0900
From: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
To: Balbir Singh <balbir@...ux.vnet.ibm.com>
Cc: linux-mm@...ck.org, YAMAMOTO Takashi <yamamoto@...inux.co.jp>,
Paul Menage <menage@...gle.com>, lizf@...fujitsu.com,
linux-kernel@...r.kernel.org,
Nick Piggin <nickpiggin@...oo.com.au>,
David Rientjes <rientjes@...gle.com>,
Pavel Emelianov <xemul@...nvz.org>,
Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
Andrew Morton <akpm@...ux-foundation.org>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
nishimura@....nes.nec.co.jp
Subject: Re: [mm] [PATCH 3/4] Memory cgroup hierarchical reclaim (v4)
Hi.
Unfortunately, trying to hold cgroup_mutex at reclaim causes dead lock.
For example, when attaching a task to some cpuset directory(memory_migrate=on),
cgroup_tasks_write (hold cgroup_mutex)
attach_task_by_pid
cgroup_attach_task
cpuset_attach
cpuset_migrate_mm
:
unmap_and_move
mem_cgroup_prepare_migration
mem_cgroup_try_charge
mem_cgroup_hierarchical_reclaim
I think similar problem can also happen when removing memcg's directory.
Any ideas?
Thanks,
Daisuke Nishimura.
On Sun, 16 Nov 2008 13:40:55 +0530, Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
> This patch introduces hierarchical reclaim. When an ancestor goes over its
> limit, the charging routine points to the parent that is above its limit.
> The reclaim process then starts from the last scanned child of the ancestor
> and reclaims until the ancestor goes below its limit.
>
> Signed-off-by: Balbir Singh <balbir@...ux.vnet.ibm.com>
> ---
>
> mm/memcontrol.c | 170 +++++++++++++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 167 insertions(+), 3 deletions(-)
>
> diff -puN mm/memcontrol.c~memcg-hierarchical-reclaim mm/memcontrol.c
> --- linux-2.6.28-rc4/mm/memcontrol.c~memcg-hierarchical-reclaim 2008-11-16 13:17:33.000000000 +0530
> +++ linux-2.6.28-rc4-balbir/mm/memcontrol.c 2008-11-16 13:17:33.000000000 +0530
> @@ -142,6 +142,13 @@ struct mem_cgroup {
> struct mem_cgroup_lru_info info;
>
> int prev_priority; /* for recording reclaim priority */
> +
> + /*
> + * While reclaiming in a hiearchy, we cache the last child we
> + * reclaimed from. Protected by cgroup_lock()
> + */
> + struct mem_cgroup *last_scanned_child;
> +
> int obsolete;
> atomic_t refcnt;
> /*
> @@ -460,6 +467,153 @@ unsigned long mem_cgroup_isolate_pages(u
> return nr_taken;
> }
>
> +static struct mem_cgroup *
> +mem_cgroup_from_res_counter(struct res_counter *counter)
> +{
> + return container_of(counter, struct mem_cgroup, res);
> +}
> +
> +/*
> + * This routine finds the DFS walk successor. This routine should be
> + * called with cgroup_mutex held
> + */
> +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;
> +
> + curr_cgroup = curr->css.cgroup;
> + root_cgroup = root_mem->css.cgroup;
> +
> + if (!list_empty(&curr_cgroup->children)) {
> + /*
> + * 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;
> + }
> +
> + /*
> + * 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;
> + }
> +
> + /*
> + * Go up to next parent and next parent's sibling if need be
> + */
> + curr_cgroup = curr_cgroup->parent;
> + goto visit_parent;
> +
> +done:
> + root_mem->last_scanned_child = curr;
> + return curr;
> +}
> +
> +/*
> + * Visit the first child (need not be the first child as per the ordering
> + * of the cgroup list, since we track last_scanned_child) of @mem and use
> + * that to reclaim free pages from.
> + */
> +static struct mem_cgroup *
> +mem_cgroup_get_first_node(struct mem_cgroup *root_mem)
> +{
> + struct cgroup *cgroup;
> + struct mem_cgroup *ret;
> + bool obsolete = (root_mem->last_scanned_child &&
> + root_mem->last_scanned_child->obsolete);
> +
> + /*
> + * Scan all children under the mem_cgroup mem
> + */
> + cgroup_lock();
> + if (list_empty(&root_mem->css.cgroup->children)) {
> + ret = root_mem;
> + goto done;
> + }
> +
> + if (!root_mem->last_scanned_child || obsolete) {
> +
> + if (obsolete)
> + mem_cgroup_put(root_mem->last_scanned_child);
> +
> + cgroup = list_first_entry(&root_mem->css.cgroup->children,
> + struct cgroup, sibling);
> + ret = mem_cgroup_from_cont(cgroup);
> + mem_cgroup_get(ret);
> + } else
> + ret = mem_cgroup_get_next_node(root_mem->last_scanned_child,
> + root_mem);
> +
> +done:
> + root_mem->last_scanned_child = ret;
> + cgroup_unlock();
> + return ret;
> +}
> +
> +/*
> + * Dance down the hierarchy if needed to reclaim memory. We remember the
> + * last child we reclaimed from, so that we don't end up penalizing
> + * one child extensively based on its position in the children list.
> + *
> + * root_mem is the original ancestor that we've been reclaim from.
> + */
> +static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
> + gfp_t gfp_mask, bool noswap)
> +{
> + struct mem_cgroup *next_mem;
> + int ret = 0;
> +
> + /*
> + * Reclaim unconditionally and don't check for return value.
> + * We need to reclaim in the current group and down the tree.
> + * One might think about checking for children before reclaiming,
> + * but there might be left over accounting, even after children
> + * have left.
> + */
> + ret = try_to_free_mem_cgroup_pages(root_mem, gfp_mask, noswap);
> + if (res_counter_check_under_limit(&root_mem->res))
> + return 0;
> +
> + next_mem = mem_cgroup_get_first_node(root_mem);
> +
> + while (next_mem != root_mem) {
> + if (next_mem->obsolete) {
> + mem_cgroup_put(next_mem);
> + cgroup_lock();
> + next_mem = mem_cgroup_get_first_node(root_mem);
> + cgroup_unlock();
> + continue;
> + }
> + ret = try_to_free_mem_cgroup_pages(next_mem, gfp_mask, noswap);
> + if (res_counter_check_under_limit(&root_mem->res)) {
> + return 0;
> + }
> + cgroup_lock();
> + next_mem = mem_cgroup_get_next_node(next_mem, root_mem);
> + cgroup_unlock();
> + }
> + return ret;
> +}
> +
> /*
> * Unlike exported interface, "oom" parameter is added. if oom==true,
> * oom-killer can be invoked.
> @@ -468,7 +622,7 @@ static int __mem_cgroup_try_charge(struc
> gfp_t gfp_mask, struct mem_cgroup **memcg,
> bool oom)
> {
> - struct mem_cgroup *mem;
> + struct mem_cgroup *mem, *mem_over_limit;
> int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
> struct res_counter *fail_res;
> /*
> @@ -514,8 +668,16 @@ static int __mem_cgroup_try_charge(struc
> if (!(gfp_mask & __GFP_WAIT))
> goto nomem;
>
> - if (try_to_free_mem_cgroup_pages(mem, gfp_mask, noswap))
> - continue;
> + /*
> + * Is one of our ancestors over their limit?
> + */
> + if (fail_res)
> + mem_over_limit = mem_cgroup_from_res_counter(fail_res);
> + else
> + mem_over_limit = mem;
> +
> + ret = mem_cgroup_hierarchical_reclaim(mem_over_limit, gfp_mask,
> + noswap);
>
> /*
> * try_to_free_mem_cgroup_pages() might not give us a full
> @@ -1710,6 +1872,8 @@ mem_cgroup_create(struct cgroup_subsys *
> res_counter_init(&mem->memsw, parent ? &parent->memsw : NULL);
>
>
> + mem->last_scanned_child = NULL;
> +
> return &mem->css;
> free_out:
> for_each_node_state(node, N_POSSIBLE)
> _
>
> --
> Balbir
>
> --
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