Re: [PATCH -mmotm 3/4] memcg: dirty pages accounting and limiting infrastructure

[Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>]

On Mon, 8 Mar 2010 11:37:11 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> On Mon, 8 Mar 2010 11:17:24 +0900
> Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:
> 
> > > But IIRC, clear_writeback is done under treelock.... No ?
> > > 
> > The place where NR_WRITEBACK is updated is out of tree_lock.
> > 
> >    1311 int test_clear_page_writeback(struct page *page)
> >    1312 {
> >    1313         struct address_space *mapping = page_mapping(page);
> >    1314         int ret;
> >    1315
> >    1316         if (mapping) {
> >    1317                 struct backing_dev_info *bdi = mapping->backing_dev_info;
> >    1318                 unsigned long flags;
> >    1319
> >    1320                 spin_lock_irqsave(&mapping->tree_lock, flags);
> >    1321                 ret = TestClearPageWriteback(page);
> >    1322                 if (ret) {
> >    1323                         radix_tree_tag_clear(&mapping->page_tree,
> >    1324                                                 page_index(page),
> >    1325                                                 PAGECACHE_TAG_WRITEBACK);
> >    1326                         if (bdi_cap_account_writeback(bdi)) {
> >    1327                                 __dec_bdi_stat(bdi, BDI_WRITEBACK);
> >    1328                                 __bdi_writeout_inc(bdi);
> >    1329                         }
> >    1330                 }
> >    1331                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
> >    1332         } else {
> >    1333                 ret = TestClearPageWriteback(page);
> >    1334         }
> >    1335         if (ret)
> >    1336                 dec_zone_page_state(page, NR_WRITEBACK);
> >    1337         return ret;
> >    1338 }
> 
> We can move this up to under tree_lock. Considering memcg, all our target has "mapping".
> 
> If we newly account bounce-buffers (for NILFS, FUSE, etc..), which has no ->mapping,
> we need much more complex new charge/uncharge theory.
> 
> But yes, adding new lock scheme seems complicated. (Sorry Andrea.)
> My concerns is performance. We may need somehing new re-implementation of
> locks/migrate/charge/uncharge.
> 
I agree. Performance is my concern too.

I made a patch below and measured the time(average of 10 times) of kernel build
on tmpfs(make -j8 on 8 CPU machine with 2.6.33 defconfig).

<before>
- root cgroup: 190.47 sec
- child cgroup: 192.81 sec

<after>
- root cgroup: 191.06 sec
- child cgroup: 193.06 sec

Hmm... about 0.3% slower for root, 0.1% slower for child.

===
From: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>

In current implementation, we don't have to disable irq at lock_page_cgroup()
because the lock is never acquired in interrupt context.
But we are going to do it in later patch, so this patch encloses all of
lock_page_cgroup()/unlock_page_cgroup() with irq_disabled()/irq_enabled().

Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
---
 mm/memcontrol.c |   17 +++++++++++++++++
 1 files changed, 17 insertions(+), 0 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 02ea959..e5ae1a1 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1359,6 +1359,7 @@ void mem_cgroup_update_file_mapped(struct page *page, int val)
 	if (unlikely(!pc))
 		return;
 
+	local_irq_disable();
 	lock_page_cgroup(pc);
 	mem = pc->mem_cgroup;
 	if (!mem)
@@ -1374,6 +1375,7 @@ void mem_cgroup_update_file_mapped(struct page *page, int val)
 
 done:
 	unlock_page_cgroup(pc);
+	local_irq_enable();
 }
 
 /*
@@ -1711,6 +1713,7 @@ struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page)
 	VM_BUG_ON(!PageLocked(page));
 
 	pc = lookup_page_cgroup(page);
+	local_irq_disable();
 	lock_page_cgroup(pc);
 	if (PageCgroupUsed(pc)) {
 		mem = pc->mem_cgroup;
@@ -1726,6 +1729,7 @@ struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page)
 		rcu_read_unlock();
 	}
 	unlock_page_cgroup(pc);
+	local_irq_enable();
 	return mem;
 }
 
@@ -1742,9 +1746,11 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *mem,
 	if (!mem)
 		return;
 
+	local_irq_disable();
 	lock_page_cgroup(pc);
 	if (unlikely(PageCgroupUsed(pc))) {
 		unlock_page_cgroup(pc);
+		local_irq_enable();
 		mem_cgroup_cancel_charge(mem);
 		return;
 	}
@@ -1775,6 +1781,7 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *mem,
 	mem_cgroup_charge_statistics(mem, pc, true);
 
 	unlock_page_cgroup(pc);
+	local_irq_enable();
 	/*
 	 * "charge_statistics" updated event counter. Then, check it.
 	 * Insert ancestor (and ancestor's ancestors), to softlimit RB-tree.
@@ -1844,12 +1851,14 @@ static int mem_cgroup_move_account(struct page_cgroup *pc,
 		struct mem_cgroup *from, struct mem_cgroup *to, bool uncharge)
 {
 	int ret = -EINVAL;
+	local_irq_disable();
 	lock_page_cgroup(pc);
 	if (PageCgroupUsed(pc) && pc->mem_cgroup == from) {
 		__mem_cgroup_move_account(pc, from, to, uncharge);
 		ret = 0;
 	}
 	unlock_page_cgroup(pc);
+	local_irq_enable();
 	/*
 	 * check events
 	 */
@@ -1981,12 +1990,15 @@ int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
 		pc = lookup_page_cgroup(page);
 		if (!pc)
 			return 0;
+		local_irq_disable();
 		lock_page_cgroup(pc);
 		if (PageCgroupUsed(pc)) {
 			unlock_page_cgroup(pc);
+			local_irq_enable();
 			return 0;
 		}
 		unlock_page_cgroup(pc);
+		local_irq_enable();
 	}
 
 	if (unlikely(!mm && !mem))
@@ -2182,6 +2194,7 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
 	if (unlikely(!pc || !PageCgroupUsed(pc)))
 		return NULL;
 
+	local_irq_disable();
 	lock_page_cgroup(pc);
 
 	mem = pc->mem_cgroup;
@@ -2222,6 +2235,7 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
 
 	mz = page_cgroup_zoneinfo(pc);
 	unlock_page_cgroup(pc);
+	local_irq_enable();
 
 	memcg_check_events(mem, page);
 	/* at swapout, this memcg will be accessed to record to swap */
@@ -2232,6 +2246,7 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
 
 unlock_out:
 	unlock_page_cgroup(pc);
+	local_irq_enable();
 	return NULL;
 }
 
@@ -2424,12 +2439,14 @@ int mem_cgroup_prepare_migration(struct page *page, struct mem_cgroup **ptr)
 		return 0;
 
 	pc = lookup_page_cgroup(page);
+	local_irq_disable();
 	lock_page_cgroup(pc);
 	if (PageCgroupUsed(pc)) {
 		mem = pc->mem_cgroup;
 		css_get(&mem->css);
 	}
 	unlock_page_cgroup(pc);
+	local_irq_enable();
 
 	if (mem) {
 		ret = __mem_cgroup_try_charge(NULL, GFP_KERNEL, &mem, false);
-- 
1.6.4

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