On Wed 18-07-12 14:26:36, Andrew Morton wrote:
>
> The patch titled
> Subject: hugetlb/cgroup: simplify pre_destroy callback
> has been added to the -mm tree. Its filename is
> hugetlb-cgroup-simplify-pre_destroy-callback.patch
>
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> ------------------------------------------------------
> From: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
> Subject: hugetlb/cgroup: simplify pre_destroy callback
>
> Since we cannot fail in hugetlb_cgroup_move_parent(), we don't really need
> to check whether cgroup have any change left after that. Also skip those
> hstates for which we don't have any charge in this cgroup.
IIUC this depends on a non-existent (cgroup) patch. I guess something
like the patch at the end should address it. I haven't tested it though
so it is not signed-off-by yet.
> Based on an earlier patch from Wanpeng Li.
>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Wanpeng Li <liwanp@xxxxxxxxxxxxxxxxxx>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> ---
>
> mm/hugetlb_cgroup.c | 49 ++++++++++++++++++------------------------
> 1 file changed, 21 insertions(+), 28 deletions(-)
>
> diff -puN mm/hugetlb_cgroup.c~hugetlb-cgroup-simplify-pre_destroy-callback mm/hugetlb_cgroup.c
> --- a/mm/hugetlb_cgroup.c~hugetlb-cgroup-simplify-pre_destroy-callback
> +++ a/mm/hugetlb_cgroup.c
> @@ -65,18 +65,6 @@ static inline struct hugetlb_cgroup *par
> return hugetlb_cgroup_from_cgroup(cg->parent);
> }
>
> -static inline bool hugetlb_cgroup_have_usage(struct cgroup *cg)
> -{
> - int idx;
> - struct hugetlb_cgroup *h_cg = hugetlb_cgroup_from_cgroup(cg);
> -
> - for (idx = 0; idx < hugetlb_max_hstate; idx++) {
> - if ((res_counter_read_u64(&h_cg->hugepage[idx], RES_USAGE)) > 0)
> - return true;
> - }
> - return false;
> -}
> -
> static struct cgroup_subsys_state *hugetlb_cgroup_create(struct cgroup *cgroup)
> {
> int idx;
> @@ -159,24 +147,29 @@ static int hugetlb_cgroup_pre_destroy(st
> {
> struct hstate *h;
> struct page *page;
> - int ret = 0, idx = 0;
> + int ret = 0, idx;
> + struct hugetlb_cgroup *h_cg = hugetlb_cgroup_from_cgroup(cgroup);
>
> - do {
> - if (cgroup_task_count(cgroup) ||
> - !list_empty(&cgroup->children)) {
> - ret = -EBUSY;
> - goto out;
> - }
> - for_each_hstate(h) {
> - spin_lock(&hugetlb_lock);
> - list_for_each_entry(page, &h->hugepage_activelist, lru)
> - hugetlb_cgroup_move_parent(idx, cgroup, page);
>
> - spin_unlock(&hugetlb_lock);
> - idx++;
> - }
> - cond_resched();
> - } while (hugetlb_cgroup_have_usage(cgroup));
> + if (cgroup_task_count(cgroup) ||
> + !list_empty(&cgroup->children)) {
> + ret = -EBUSY;
> + goto out;
> + }
> +
> + for_each_hstate(h) {
> + /*
> + * if we don't have any charge, skip this hstate
> + */
> + idx = hstate_index(h);
> + if (res_counter_read_u64(&h_cg->hugepage[idx], RES_USAGE) == 0)
> + continue;
> + spin_lock(&hugetlb_lock);
> + list_for_each_entry(page, &h->hugepage_activelist, lru)
> + hugetlb_cgroup_move_parent(idx, cgroup, page);
> + spin_unlock(&hugetlb_lock);
> + VM_BUG_ON(res_counter_read_u64(&h_cg->hugepage[idx], RES_USAGE));
> + }
> out:
> return ret;
> }
> _
---
>From 621ed1c9dab63bd82205bd5266eb9974f86a0a3f Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@xxxxxxx>
Date: Thu, 19 Jul 2012 13:23:23 +0200
Subject: [PATCH] cgroup: keep cgroup_mutex locked for pre_destroy
3fa59dfb (cgroup: fix potential deadlock in pre_destroy) dropped the
cgroup_mutex lock while calling pre_destroy callbacks because memory
controller could deadlock because force_empty triggered reclaim.
Since "memcg: move charges to root cgroup if use_hierarchy=0" there is
no reclaim going on from mem_cgroup_force_empty though so we can safely
keep the cgroup_mutex locked. This has an advantage that no tasks might
be added during pre_destroy callback and so the handlers don't have to
consider races when new tasks add new charges. This simplifies the
implementation.
---
kernel/cgroup.c | 2 --
1 file changed, 2 deletions(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 0f3527d..9dba05d 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4181,7 +4181,6 @@ again:
mutex_unlock(&cgroup_mutex);
return -EBUSY;
}
- mutex_unlock(&cgroup_mutex);
/*
* In general, subsystem has no css->refcnt after pre_destroy(). But
@@ -4204,7 +4203,6 @@ again:
return ret;
}
- mutex_lock(&cgroup_mutex);
parent = cgrp->parent;
if (atomic_read(&cgrp->count) || !list_empty(&cgrp->children)) {
clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
--
1.7.10.4
--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic
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