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Date: Wed, 22 Apr 2009 17:53:23 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To: "linux-mm@...ck.org" <linux-mm@...ck.org>
Cc: "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: [RFC][PATCH] memcg: relax force empty loop
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Andrew Morton pointed out that force_empty() may work too long and
will cause unpleasant delay or dead-lock around page isolation.
This patch rewrites memcg's force_empty to do
- avoid trylock, just use lock_page_cgroup().
- When it has worked for a long time, take a rest for a while.
The logic is.
- move 32 pages at most per one trial.
- if there are still pages remaining and we have more time, retry.
- if work time(HZ/10) elapsed, check we should sleep or not.
Concern:
- this may make rmdir() dramatically slow because this uses
schedule_timeout() for relaxing.
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
---
include/linux/page_cgroup.h | 5 --
mm/memcontrol.c | 87 +++++++++++++++++++++++++++++++-------------
2 files changed, 62 insertions(+), 30 deletions(-)
Index: mmotm-2.6.30-Apr21/mm/memcontrol.c
===================================================================
--- mmotm-2.6.30-Apr21.orig/mm/memcontrol.c
+++ mmotm-2.6.30-Apr21/mm/memcontrol.c
@@ -1148,8 +1148,7 @@ static int mem_cgroup_move_account(struc
from_mz = mem_cgroup_zoneinfo(from, nid, zid);
to_mz = mem_cgroup_zoneinfo(to, nid, zid);
- if (!trylock_page_cgroup(pc))
- return ret;
+ lock_page_cgroup(pc);
if (!PageCgroupUsed(pc))
goto out;
@@ -1807,33 +1806,38 @@ int mem_cgroup_resize_memsw_limit(struct
}
/*
- * This routine traverse page_cgroup in given list and drop them all.
- * *And* this routine doesn't reclaim page itself, just removes page_cgroup.
+ * This routine moves all accounts to it parents. Returns 0 if the list
+ * comes to be empty. move 256 pages at most in each turn and returns EAGAIN
+ * if time is over.
*/
-static int mem_cgroup_force_empty_list(struct mem_cgroup *mem,
- int node, int zid, enum lru_list lru)
+#define NR_MOVE_ACCOUNT_THRESH (32) /* 128kbytes if page size is 4k */
+
+static long mem_cgroup_force_empty_list(struct mem_cgroup *mem, int node,
+ int zid, enum lru_list lru,
+ unsigned long next_wait)
{
struct zone *zone;
struct mem_cgroup_per_zone *mz;
struct page_cgroup *pc, *busy;
- unsigned long flags, loop;
+ unsigned long flags, scan, failure;
struct list_head *list;
- int ret = 0;
+ int ret;
zone = &NODE_DATA(node)->node_zones[zid];
mz = mem_cgroup_zoneinfo(mem, node, zid);
list = &mz->lists[lru];
- loop = MEM_CGROUP_ZSTAT(mz, lru);
- /* give some margin against EBUSY etc...*/
- loop += 256;
+ /* The number of pages to be scanned in this turn */
+retry:
+ scan = NR_MOVE_ACCOUNT_THRESH;
busy = NULL;
- while (loop--) {
- ret = 0;
+ while (scan--) {
+
spin_lock_irqsave(&zone->lru_lock, flags);
if (list_empty(list)) {
spin_unlock_irqrestore(&zone->lru_lock, flags);
- break;
+ /* SUCCESS! */
+ return 0;
}
pc = list_entry(list->prev, struct page_cgroup, lru);
if (busy == pc) {
@@ -1845,32 +1849,47 @@ static int mem_cgroup_force_empty_list(s
spin_unlock_irqrestore(&zone->lru_lock, flags);
ret = mem_cgroup_move_parent(pc, mem, GFP_KERNEL);
+
if (ret == -ENOMEM)
- break;
+ return ret;
if (ret == -EBUSY || ret == -EINVAL) {
/* found lock contention or "pc" is obsolete. */
busy = pc;
cond_resched();
+ /* EBUSY check is done in other logic, finally */
+ failure++;
} else
busy = NULL;
}
+ /* List is not empty yet....*/
- if (!ret && !list_empty(list))
+ /* Some busy pages ? (needs lru_add_drain() */
+ if (failure)
return -EBUSY;
- return ret;
+
+ /* need to revisit this zone */
+ if (!time_after(jiffies, next_wait))
+ goto retry;
+
+ return -EAGAIN;
}
/*
* make mem_cgroup's charge to be 0 if there is no task.
* This enables deleting this mem_cgroup.
*/
+
+#define FORCE_EMPTY_RELAX_TICK (HZ/20)
+#define FORCE_EMPTY_WORK_TICK (HZ/10)
+
static int mem_cgroup_force_empty(struct mem_cgroup *mem, bool free_all)
{
int ret;
int node, zid, shrink;
int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
struct cgroup *cgrp = mem->css.cgroup;
+ unsigned long next_wait;
css_get(&mem->css);
@@ -1879,6 +1898,10 @@ static int mem_cgroup_force_empty(struct
if (free_all)
goto try_to_free;
move_account:
+ /* This is for making all *used* pages to be on LRU. */
+ lru_add_drain_all();
+
+ next_wait = jiffies + FORCE_EMPTY_WORK_TICK;
while (mem->res.usage > 0) {
ret = -EBUSY;
if (cgroup_task_count(cgrp) || !list_empty(&cgrp->children))
@@ -1886,26 +1909,40 @@ move_account:
ret = -EINTR;
if (signal_pending(current))
goto out;
- /* This is for making all *used* pages to be on LRU. */
- lru_add_drain_all();
ret = 0;
for_each_node_state(node, N_HIGH_MEMORY) {
- for (zid = 0; !ret && zid < MAX_NR_ZONES; zid++) {
+ for (zid = 0; zid < MAX_NR_ZONES; zid++) {
enum lru_list l;
for_each_lru(l) {
- ret = mem_cgroup_force_empty_list(mem,
- node, zid, l);
- if (ret)
+ ret = mem_cgroup_force_empty_list(
+ mem, node, zid, l, next_wait);
+ if (ret < 0)
break;
}
}
- if (ret)
+ if (ret < 0)
break;
}
/* it seems parent cgroup doesn't have enough mem */
if (ret == -ENOMEM)
goto try_to_free;
- cond_resched();
+ /*
+ * It seems some page are off-LRU. Give chance to others and
+ * sleep until flush. This will wait for kevent workq.
+ */
+ if (ret == -EBUSY)
+ lru_add_drain_all();
+
+ if (cond_resched())
+ next_wait = jiffies + FORCE_EMPTY_WORK_TICK;
+ else if (ret == -EAGAIN || time_after(jiffies, next_wait)) {
+ /* release this cpu for a while. If we could release
+ * cpu by cond_resched(), we don't come here.
+ */
+ schedule_timeout(FORCE_EMPTY_RELAX_TICK);
+ next_wait = jiffies + FORCE_EMPTY_WORK_TICK;
+ }
+
}
ret = 0;
out:
Index: mmotm-2.6.30-Apr21/include/linux/page_cgroup.h
===================================================================
--- mmotm-2.6.30-Apr21.orig/include/linux/page_cgroup.h
+++ mmotm-2.6.30-Apr21/include/linux/page_cgroup.h
@@ -61,11 +61,6 @@ static inline void lock_page_cgroup(stru
bit_spin_lock(PCG_LOCK, &pc->flags);
}
-static inline int trylock_page_cgroup(struct page_cgroup *pc)
-{
- return bit_spin_trylock(PCG_LOCK, &pc->flags);
-}
-
static inline void unlock_page_cgroup(struct page_cgroup *pc)
{
bit_spin_unlock(PCG_LOCK, &pc->flags);
--
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