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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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