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SubjectRe: [PATCH -mmotm 3/4] memcg: dirty pages accounting and limiting infrastructure
On Mon, Mar 08, 2010 at 05:07:11PM +0900, Daisuke Nishimura wrote:
> 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.

Thanks Daisuke-san. This doesn't seem too bad, I'll repeat the test on
my machine and compare performance with my patch + your and Kame-san
fixes. Even if I agree that adding multiple locked/unlocked versions of
mem_cgroup_update_page_stat() it's just too bug-prone...

Thanks,
-Andrea

>
> ===
> 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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