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

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Message-Id: <20100722182204.81dddfa9.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Thu, 22 Jul 2010 18:22:04 +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 Thu, 22 Jul 2010 10:19:30 +0100
Mel Gorman <mel@....ul.ie> wrote:

> On Thu, Jul 22, 2010 at 08:57:34AM +0900, KAMEZAWA Hiroyuki wrote:
> > On Wed, 21 Jul 2010 15:27:10 +0100
> > Mel Gorman <mel@....ul.ie> wrote:

> > 1 tick penalty seems too large. I hope we can have some waitqueue in future.
> > 
> 
> congestion_wait() if congestion occurs goes onto a waitqueue that is
> woken if congestion clears. I didn't measure it this time around but I
> doubt it waits for HZ/10 much of the time.
> 
Okay.

> > > > > -		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 ?
> > 
> 
> Both direct reclaim and kswapd can reach shrink_inactive_list
> 
> Direct reclaim
> do_try_to_free_pages
>   -> shrink_zones
>     -> shrink_zone
>       -> shrink_list
>         -> shrink_inactive list <--- the routine in question
> 
> Kswapd
> balance_pgdat
>   -> shrink_zone
>     -> shrink_list
>       -> shrink_inactive_list
> 
> pageout() is still called by direct reclaim if the page is anon so it
> will synchronously wait on those if PAGEOUT_IO_SYNC is set. 

Ah, ok. I missed that. Thank you for kindly clarification.

Thanks,
-Kame

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