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Date: Wed, 10 Mar 2010 10:43:09 +0900
From: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
To: balbir@...ux.vnet.ibm.com
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
Andrea Righi <arighi@...eler.com>,
Vivek Goyal <vgoyal@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Trond Myklebust <trond.myklebust@....uio.no>,
Suleiman Souhlal <suleiman@...gle.com>,
Greg Thelen <gthelen@...gle.com>,
"Kirill A. Shutemov" <kirill@...temov.name>,
Andrew Morton <akpm@...ux-foundation.org>,
containers@...ts.linux-foundation.org,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Subject: Re: [PATCH mmotm 2.5/4] memcg: disable irq at page cgroup lock (Re:
[PATCH -mmotm 3/4] memcg: dirty pages accounting and limiting
infrastructure)
> Please please measure the performance overhead of this change.
>
here.
> > > > > > 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
> > > > > >
<after2(local_irq_save/restore)>
- root cgroup: 191.42 sec
- child cgroup: 193.55 sec
hmm, I think it's in error range, but I can see a tendency by testing several times
that it's getting slower as I add additional codes. Using local_irq_disable()/enable()
except in mem_cgroup_update_file_mapped(it can be the only candidate to be called
with irq disabled in future) might be the choice.
Thanks,
Daisuke Nishimura.
On Tue, 9 Mar 2010 10:20:58 +0530, Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
> * nishimura@....nes.nec.co.jp <nishimura@....nes.nec.co.jp> [2010-03-09 10:29:28]:
>
> > On Tue, 9 Mar 2010 09:19:14 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> > > On Tue, 9 Mar 2010 01:12:52 +0100
> > > Andrea Righi <arighi@...eler.com> wrote:
> > >
> > > > 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@....nes.nec.co.jp> wrote:
> > > > >
> > > > > > On Mon, 8 Mar 2010 11:37:11 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> > > > > > > On Mon, 8 Mar 2010 11:17:24 +0900
> > > > > > > Daisuke Nishimura <nishimura@....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?
> > > maybe.
> > >
> > > > Anyway, it would make the code much more readable...
> > > >
> > > ok.
> > >
> > > please go ahead in this direction. Nishimura-san, would you post an
> > > independent patch ? If no, Andrea-san, please.
> > >
> > This is the updated version.
> >
> > Andrea-san, can you merge this into your patch set ?
> >
>
> Please please measure the performance overhead of this change.
>
> --
> Three Cheers,
> Balbir
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