linux-kernel - Re: [patch 6/9] mm + fs: store shadow entries in page cache

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Message-ID: <20131127164544.GC3556@cmpxchg.org>
Date:	Wed, 27 Nov 2013 11:45:44 -0500
From:	Johannes Weiner <hannes@...xchg.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Dave Chinner <david@...morbit.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>, Jan Kara <jack@...e.cz>,
	Vlastimil Babka <vbabka@...e.cz>, Tejun Heo <tj@...nel.org>,
	Andi Kleen <andi@...stfloor.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Greg Thelen <gthelen@...gle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Hugh Dickins <hughd@...gle.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Mel Gorman <mgorman@...e.de>,
	Minchan Kim <minchan.kim@...il.com>,
	Michel Lespinasse <walken@...gle.com>,
	Seth Jennings <sjenning@...ux.vnet.ibm.com>,
	Roman Gushchin <klamm@...dex-team.ru>,
	Ozgun Erdogan <ozgun@...usdata.com>,
	Metin Doslu <metin@...usdata.com>, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 6/9] mm + fs: store shadow entries in page cache

On Tue, Nov 26, 2013 at 11:20:53AM +0100, Peter Zijlstra wrote:
> On Tue, Nov 26, 2013 at 10:17:16AM +1100, Dave Chinner wrote:
> > void truncate_inode_pages_final(struct address_space *mapping)
> > {
> > 	mapping_set_exiting(mapping);
> > 	if (inode->i_data.nrpages || inode->i_data.nrshadows) {
> > 		/*
> > 		 * spinlock barrier to ensure all modifications are
> > 		 * complete before we do the final truncate
> > 		 */
> > 		spin_lock_irq(&mapping->tree_lock);
> > 		spin_unlock_irq(&mapping->tree_lock);
> 
> 	spin_unlock_wait() ?
> 
> Its cheaper, but prone to starvation; its typically useful when you're
> waiting for the last owner to go away and know there won't be any new
> ones around.

The other side is reclaim plucking pages one-by-one from the address
space in LRU order.  It'd be preferable to not starve the truncation
side, because it is much more efficient at getting rid of those pages.
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