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Message-Id: <20111221172423.5d036cdd.kamezawa.hiroyu@jp.fujitsu.com>
Date: Wed, 21 Dec 2011 17:24:23 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>, cgroups@...r.kernel.org,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"hannes@...xchg.org" <hannes@...xchg.org>,
Michal Hocko <mhocko@...e.cz>, Hugh Dickins <hughd@...gle.com>
Subject: [PATCH v2] memcg: return -EINTR at bypassing try_charge().
How about this ?
--
>From 6076425613f594d442c58a5d463c09f8309236aa Mon Sep 17 00:00:00 2001
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Date: Wed, 21 Dec 2011 16:27:25 +0900
Subject: [PATCH] memcg: return -EINTR at bypassing try_charge().
This patch is a fix for memcg-simplify-lru-handling-by-new-rule.patch
When running testprogram and stop it by Ctrl-C, add_lru/del_lru
will find pc->mem_cgroup is NULL and get panic. The reason
is bypass code in try_charge().
At try_charge(), it checks the thread is fatal or not as..
fatal_signal_pending() or TIF_MEMDIE. In this case, __try_charge()
returns 0(success) with setting *ptr as NULL.
Now, lruvec are deteremined by pc->mem_cgroup. So, it's better
to reset pc->mem_cgroup as root_mem_cgroup. This patch does
following change in try_charge()
1. return -EINTR at bypassing.
2. set *ptr = root_mem_cgroup at bypassing.
By this change, in page fault / radix-tree-insert path,
the page will be charged against root_mem_cgroup and the thread's
operations will go ahead without trouble. In other path,
migration or move_account etc..., -EINTR will stop the operation.
(may need some cleanup later..)
After this change, pc->mem_cgroup will have valid pointer if
the page is used.
Changelog: v1 -> v2
- returns -EINTR at bypassing.
- change error code handling at callers.
- changed the name of patch.
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
---
mm/memcontrol.c | 53 +++++++++++++++++++++++++++++++++++++++++------------
1 files changed, 41 insertions(+), 12 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9175097..3c6eb7e 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2185,6 +2185,23 @@ static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
}
/*
+ * __mem_cgroup_try_charge() does
+ * 1. detect memcg to be charged against from passed *mm and *ptr,
+ * 2. update res_counter
+ * 3. call memory reclaim if necessary.
+ *
+ * In some special case, if the task is fatal, fatal_signal_pending() or
+ * TIF_MEMDIE or ->mm is NULL, this functoion returns -EINTR with filling
+ * *ptr as root_mem_cgroup. There are 2 reasons for this. 1st is that
+ * fatal threads should quit as soon as possible without any hazards.
+ * 2nd is that all page should have valid pc->mem_cgroup if it will be
+ * used.
+ *
+ * So, try_charge will return
+ * 0 ... at success. filling *ptr with a valid memcg pointer.
+ * -ENOMEM ... charge failure because of resource limits.
+ * -EINTR ... if thread is fatal. *ptr is filled with root_mem_cgroup.
+ *
* Unlike exported interface, "oom" parameter is added. if oom==true,
* oom-killer can be invoked.
*/
@@ -2316,8 +2333,8 @@ nomem:
*ptr = NULL;
return -ENOMEM;
bypass:
- *ptr = NULL;
- return 0;
+ *ptr = root_mem_cgroup;
+ return -EINTR;
}
/*
@@ -2564,7 +2581,7 @@ static int mem_cgroup_move_parent(struct page *page,
{
struct cgroup *cg = child->css.cgroup;
struct cgroup *pcg = cg->parent;
- struct mem_cgroup *parent;
+ struct mem_cgroup *parent, *ptr;
unsigned int nr_pages;
unsigned long uninitialized_var(flags);
int ret;
@@ -2582,8 +2599,8 @@ static int mem_cgroup_move_parent(struct page *page,
nr_pages = hpage_nr_pages(page);
parent = mem_cgroup_from_cont(pcg);
- ret = __mem_cgroup_try_charge(NULL, gfp_mask, nr_pages, &parent, false);
- if (ret || !parent)
+ ret = __mem_cgroup_try_charge(NULL, gfp_mask, nr_pages, &ptr, false);
+ if (ret)
goto put_back;
if (nr_pages > 1)
@@ -2630,9 +2647,9 @@ static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm,
pc = lookup_page_cgroup(page);
ret = __mem_cgroup_try_charge(mm, gfp_mask, nr_pages, &memcg, oom);
- if (ret || !memcg)
+ if (ret == -ENOMEM)
return ret;
-
+ /* we'll bypass -EINTR case and charge this page to root memcg */
__mem_cgroup_commit_charge(memcg, page, nr_pages, pc, ctype);
return 0;
}
@@ -2703,6 +2720,7 @@ int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
ret = mem_cgroup_charge_common(page, mm, gfp_mask, type);
else { /* page is swapcache/shmem */
ret = mem_cgroup_try_charge_swapin(mm, page, gfp_mask, &memcg);
+ /* see try_charge_swapi() for -EINTR case */
if (!ret)
__mem_cgroup_commit_charge_swapin(page, memcg, type);
}
@@ -2743,11 +2761,21 @@ int mem_cgroup_try_charge_swapin(struct mm_struct *mm,
*memcgp = memcg;
ret = __mem_cgroup_try_charge(NULL, mask, 1, memcgp, true);
css_put(&memcg->css);
+ /*
+ * If this thread is fatal, charge against root cgroup and allow
+ * this thread to exit in quick manner. EINTR is not handled
+ * in page fault path. So, just bypass this.
+ */
+ if (ret == -EINTR)
+ ret = 0;
return ret;
charge_cur_mm:
if (unlikely(!mm))
mm = &init_mm;
- return __mem_cgroup_try_charge(mm, mask, 1, memcgp, true);
+ ret = __mem_cgroup_try_charge(mm, mask, 1, memcgp, true);
+ if (ret == -EINTR)
+ ret = 0;
+ return ret;
}
static void
@@ -3205,7 +3233,7 @@ int mem_cgroup_prepare_migration(struct page *page,
*memcgp = memcg;
ret = __mem_cgroup_try_charge(NULL, gfp_mask, 1, memcgp, false);
css_put(&memcg->css);/* drop extra refcnt */
- if (ret || *memcgp == NULL) {
+ if (ret) {
if (PageAnon(page)) {
lock_page_cgroup(pc);
ClearPageCgroupMigration(pc);
@@ -3215,6 +3243,7 @@ int mem_cgroup_prepare_migration(struct page *page,
*/
mem_cgroup_uncharge_page(page);
}
+ /* we'll need to revisit this error code (we have -EINTR) */
return -ENOMEM;
}
/*
@@ -3633,7 +3662,7 @@ static int mem_cgroup_force_empty_list(struct mem_cgroup *memcg,
pc = lookup_page_cgroup(page);
ret = mem_cgroup_move_parent(page, pc, memcg, GFP_KERNEL);
- if (ret == -ENOMEM)
+ if (ret == -ENOMEM || ret == -EINTR)
break;
if (ret == -EBUSY || ret == -EINVAL) {
@@ -5091,9 +5120,9 @@ one_by_one:
}
ret = __mem_cgroup_try_charge(NULL,
GFP_KERNEL, 1, &memcg, false);
- if (ret || !memcg)
+ if (ret)
/* mem_cgroup_clear_mc() will do uncharge later */
- return -ENOMEM;
+ return ret;
mc.precharge++;
}
return ret;
--
1.7.4.1
--
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