Re: [PATCH 00/10] memcg: per cgroup dirty page accounting
From: KAMEZAWA Hiroyuki
Date: Mon Oct 18 2010 - 02:02:06 EST
On Sun, 3 Oct 2010 23:57:55 -0700
Greg Thelen <gthelen@xxxxxxxxxx> wrote:
> Greg Thelen (10):
> memcg: add page_cgroup flags for dirty page tracking
> memcg: document cgroup dirty memory interfaces
> memcg: create extensible page stat update routines
> memcg: disable local interrupts in lock_page_cgroup()
> memcg: add dirty page accounting infrastructure
> memcg: add kernel calls for memcg dirty page stats
> memcg: add dirty limits to mem_cgroup
> memcg: add cgroupfs interface to memcg dirty limits
> writeback: make determine_dirtyable_memory() static.
> memcg: check memcg dirty limits in page writeback
Greg, this is a patch on your set.
mmotm-1014
- memcg-reduce-lock-hold-time-during-charge-moving.patch
(I asked Andrew to drop this)
+ your 1,2,3,5,6,7,8,9,10 (dropped patch "4")
I'm grad if you merge this to your set as replacement of "4".
I'll prepare a performance improvement patch and post it if this dirty_limit
patches goes to -mm.
Thank you for your work.
==
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Now, at supporing dirty limit, there is a deadlock problem in accounting.
1. If pages are being migrated from a memcg, then updates to that
memcg page statistics are protected by grabbing a bit spin lock
using lock_page_cgroup(). In recent changes of dirty page accounting
is updating memcg page accounting (specifically: num writeback pages)
from IRQ context (softirq). Avoid a deadlocking nested spin lock attempt
by irq on the local processor when grabbing the page_cgroup.
2. lock for update_stat is used only for avoiding race with move_account().
So, IRQ awareness of lock_page_cgroup() itself is not a problem. The problem
is in update_stat() and move_account().
Then, this reworks locking scheme of update_stat() and move_account() by
adding new lock bit PCG_MOVE_LOCK, which is always taken under IRQ disable.
Trade-off
* using lock_page_cgroup() + disable IRQ has some impacts on performance
and I think it's bad to disable IRQ when it's not necessary.
* adding a new lock makes move_account() slow. Score is here.
Peformance Impact: moving a 8G anon process.
Before:
real 0m0.792s
user 0m0.000s
sys 0m0.780s
After:
real 0m0.854s
user 0m0.000s
sys 0m0.842s
This score is bad but planned patches for optimization can reduce
this impact.
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
---
include/linux/page_cgroup.h | 31 ++++++++++++++++++++++++++++---
mm/memcontrol.c | 9 +++++++--
2 files changed, 35 insertions(+), 5 deletions(-)
Index: dirty_limit_new/include/linux/page_cgroup.h
===================================================================
--- dirty_limit_new.orig/include/linux/page_cgroup.h
+++ dirty_limit_new/include/linux/page_cgroup.h
@@ -35,15 +35,18 @@ struct page_cgroup *lookup_page_cgroup(s
enum {
/* flags for mem_cgroup */
- PCG_LOCK, /* page cgroup is locked */
+ PCG_LOCK, /* Lock for pc->mem_cgroup and following bits. */
PCG_CACHE, /* charged as cache */
PCG_USED, /* this object is in use. */
- PCG_ACCT_LRU, /* page has been accounted for */
+ PCG_MIGRATION, /* under page migration */
+ /* flags for mem_cgroup and file and I/O status */
+ PCG_MOVE_LOCK, /* For race between move_account v.s. following bits */
PCG_FILE_MAPPED, /* page is accounted as "mapped" */
PCG_FILE_DIRTY, /* page is dirty */
PCG_FILE_WRITEBACK, /* page is under writeback */
PCG_FILE_UNSTABLE_NFS, /* page is NFS unstable */
- PCG_MIGRATION, /* under page migration */
+ /* No lock in page_cgroup */
+ PCG_ACCT_LRU, /* page has been accounted for (under lru_lock) */
};
#define TESTPCGFLAG(uname, lname) \
@@ -119,6 +122,10 @@ static inline enum zone_type page_cgroup
static inline void lock_page_cgroup(struct page_cgroup *pc)
{
+ /*
+ * Don't take this lock in IRQ context.
+ * This lock is for pc->mem_cgroup, USED, CACHE, MIGRATION
+ */
bit_spin_lock(PCG_LOCK, &pc->flags);
}
@@ -127,6 +134,24 @@ static inline void unlock_page_cgroup(st
bit_spin_unlock(PCG_LOCK, &pc->flags);
}
+static inline void move_lock_page_cgroup(struct page_cgroup *pc,
+ unsigned long *flags)
+{
+ /*
+ * We know updates to pc->flags of page cache's stats are from both of
+ * usual context or IRQ context. Disable IRQ to avoid deadlock.
+ */
+ local_irq_save(*flags);
+ bit_spin_lock(PCG_MOVE_LOCK, &pc->flags);
+}
+
+static inline void move_unlock_page_cgroup(struct page_cgroup *pc,
+ unsigned long *flags)
+{
+ bit_spin_unlock(PCG_MOVE_LOCK, &pc->flags);
+ local_irq_restore(*flags);
+}
+
#else /* CONFIG_CGROUP_MEM_RES_CTLR */
struct page_cgroup;
Index: dirty_limit_new/mm/memcontrol.c
===================================================================
--- dirty_limit_new.orig/mm/memcontrol.c
+++ dirty_limit_new/mm/memcontrol.c
@@ -1784,6 +1784,7 @@ void mem_cgroup_update_page_stat(struct
struct mem_cgroup *mem;
struct page_cgroup *pc = lookup_page_cgroup(page);
bool need_unlock = false;
+ unsigned long uninitialized_var(flags);
if (unlikely(!pc))
return;
@@ -1795,7 +1796,7 @@ void mem_cgroup_update_page_stat(struct
/* pc->mem_cgroup is unstable ? */
if (unlikely(mem_cgroup_stealed(mem))) {
/* take a lock against to access pc->mem_cgroup */
- lock_page_cgroup(pc);
+ move_lock_page_cgroup(pc, &flags);
need_unlock = true;
mem = pc->mem_cgroup;
if (!mem || !PageCgroupUsed(pc))
@@ -1856,7 +1857,7 @@ void mem_cgroup_update_page_stat(struct
out:
if (unlikely(need_unlock))
- unlock_page_cgroup(pc);
+ move_unlock_page_cgroup(pc, &flags);
rcu_read_unlock();
return;
}
@@ -2426,9 +2427,13 @@ static int mem_cgroup_move_account(struc
struct mem_cgroup *from, struct mem_cgroup *to, bool uncharge)
{
int ret = -EINVAL;
+ unsigned long flags;
+
lock_page_cgroup(pc);
if (PageCgroupUsed(pc) && pc->mem_cgroup == from) {
+ move_lock_page_cgroup(pc, &flags);
__mem_cgroup_move_account(pc, from, to, uncharge);
+ move_unlock_page_cgroup(pc, &flags);
ret = 0;
}
unlock_page_cgroup(pc);
--
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