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

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Message-ID: <20100721142710.GZ13117@csn.ul.ie>
Date:	Wed, 21 Jul 2010 15:27:10 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
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, Jul 21, 2010 at 09:01:11PM +0900, KAMEZAWA Hiroyuki wrote:
> > <SNIP>
> >  
> >  	/*
> > -	 * If we are direct reclaiming for contiguous pages and we do
> > +	 * If specific pages are needed such as with direct reclaiming
> > +	 * for contiguous pages or for memory containers and we do
> >  	 * not reclaim everything in the list, try again and wait
> > -	 * for IO to complete. This will stall high-order allocations
> > -	 * but that should be acceptable to the caller
> > +	 * for IO to complete. This will stall callers that require
> > +	 * specific pages but it should be acceptable to the caller
> >  	 */
> > -	if (nr_reclaimed < nr_taken && !current_is_kswapd() &&
> > -			sc->lumpy_reclaim_mode) {
> > -		congestion_wait(BLK_RW_ASYNC, HZ/10);
> > +	if (sc->may_writepage && !current_is_kswapd() &&
> > +			(sc->lumpy_reclaim_mode || sc->mem_cgroup)) {
> > +		int dirty_retry = MAX_SWAP_CLEAN_WAIT;
> 
> Hmm, ok. I see what will happen to memcg.

Thanks

> 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.

> >  
> > -		/*
> > -		 * 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.

> > -		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.

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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