[Devel] Re: [PATCH -mmotm 3/4] memcg: dirty pages accounting and limiting infrastructure
Andrea Righi
arighi at develer.com
Mon Mar 8 16:15:40 PST 2010
On Mon, Mar 08, 2010 at 05:31:00PM +0900, KAMEZAWA Hiroyuki wrote:
> On Mon, 8 Mar 2010 17:07:11 +0900
> Daisuke Nishimura <nishimura at mxp.nes.nec.co.jp> wrote:
>
> > On Mon, 8 Mar 2010 11:37:11 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu at jp.fujitsu.com> wrote:
> > > On Mon, 8 Mar 2010 11:17:24 +0900
> > > Daisuke Nishimura <nishimura at 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.
> >
>
> Hmm...accepatable ? (sounds it's in error-range)
>
> BTW, why local_irq_disable() ?
> local_irq_save()/restore() isn't better ?
Probably there's not the overhead of saving flags? Anyway, it would make
the code much more readable...
Thanks,
-Andrea
>
> Thanks,
> -Kame
>
> > ===
> > From: Daisuke Nishimura <nishimura at 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 at 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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