linux-kernel - Re: [PATCH 4/8] vmscan: Do not writeback filesystem pages in direct reclaim

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Date:	Thu, 22 Jul 2010 08:57:34 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Johannes Weiner <hannes@...xchg.org>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
	Dave Chinner <david@...morbit.com>,
	Chris Mason <chris.mason@...cle.com>,
	Nick Piggin <npiggin@...e.de>, Rik van Riel <riel@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH 4/8] vmscan: Do not writeback filesystem pages in direct
 reclaim

On Wed, 21 Jul 2010 15:27:10 +0100
Mel Gorman <mel@....ul.ie> wrote:

> On Wed, Jul 21, 2010 at 09:01:11PM +0900, KAMEZAWA Hiroyuki wrote:
 
> > But, hmm, memcg will have to select to enter this rounine based on
> > the result of 1st memory reclaim.
> > 
> 
> It has the option of igoring pages being dirtied but I worry that the
> container could be filled with dirty pages waiting for flushers to do
> something.

I'll prepare dirty_ratio for memcg. It's not easy but requested by I/O cgroup
guys, too...


> 
> > >  
> > > -		/*
> > > -		 * The attempt at page out may have made some
> > > -		 * of the pages active, mark them inactive again.
> > > -		 */
> > > -		nr_active = clear_active_flags(&page_list, NULL);
> > > -		count_vm_events(PGDEACTIVATE, nr_active);
> > > +		while (nr_reclaimed < nr_taken && nr_dirty && dirty_retry--) {
> > > +			wakeup_flusher_threads(laptop_mode ? 0 : nr_dirty);
> > > +			congestion_wait(BLK_RW_ASYNC, HZ/10);
> > >  
> >
> > Congestion wait is required ?? Where the congestion happens ?
> > I'm sorry you already have some other trick in other patch.
> > 
> 
> It's to wait for the IO to occur.
> 
1 tick penalty seems too large. I hope we can have some waitqueue in future.



> > > -		nr_reclaimed += shrink_page_list(&page_list, sc, PAGEOUT_IO_SYNC);
> > > +			/*
> > > +			 * The attempt at page out may have made some
> > > +			 * of the pages active, mark them inactive again.
> > > +			 */
> > > +			nr_active = clear_active_flags(&page_list, NULL);
> > > +			count_vm_events(PGDEACTIVATE, nr_active);
> > > +	
> > > +			nr_reclaimed += shrink_page_list(&page_list, sc,
> > > +						PAGEOUT_IO_SYNC, &nr_dirty);
> > > +		}
> > 
> > Just a question. This PAGEOUT_IO_SYNC has some meanings ?
> > 
> 
> Yes, in pageout it will wait on pages currently being written back to be
> cleaned before trying to reclaim them.
> 
Hmm. IIUC, this routine is called only when !current_is_kswapd() and
pageout is done only whne current_is_kswapd(). So, this seems ....
Wrong ?

Thanks,
-Kame




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