linux-ext4 - Re: [PATCH 7/7 v2] ext4: reclaim extents from extent status tree

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Date:	Mon, 21 Jan 2013 23:12:36 +0800
From:	Zheng Liu <gnehzuil.liu@...il.com>
To:	Jan Kara <jack@...e.cz>
Cc:	Theodore Ts'o <tytso@....edu>, linux-ext4@...r.kernel.org,
	Zheng Liu <wenqing.lz@...bao.com>
Subject: Re: [PATCH 7/7 v2] ext4: reclaim extents from extent status tree

On Mon, Jan 21, 2013 at 03:43:36PM +0100, Jan Kara wrote:
> On Fri 18-01-13 00:39:47, Ted Tso wrote:
> > On Fri, Jan 18, 2013 at 12:19:21AM -0500, Theodore Ts'o wrote:
> > > I'm a bit concerned we might be too aggressive,
> > > because there are two ways that items can be freed from the
> > > extent_status tree.  One is if the inode is not used at all, and when
> > > we release the inode, we'll drop all of the entries in the
> > > extent_status_tree for that inode.  The second way is via the shrinker
> > > which we've registered.
> > 
> > If we use the sb->s_op->free_cached_objects() approach, something like
> > the following change to prune_super() in fs/super.c might address the
> > above concern:
>   Yeah, this would make sence to me. When you submit the final patch don't
> forget to include Dave Chinner. He's the author of the shrinker framework
> and XFS uses nr_cached_objects / free_cached_objects. AFAICS it uses it for
> its separate inode cache so your change shouldn't affect it but better be
> sure.

Thanks for reminding.  This patch has been added in my patch series, and
I will CC' it to Dave.

Regards,
                                                - Zheng

> > 
> > diff --git a/fs/super.c b/fs/super.c
> > index 12f1237..fb57bd2 100644
> > --- a/fs/super.c
> > +++ b/fs/super.c
> > @@ -80,6 +80,7 @@ static int prune_super(struct shrinker *shrink, struct shrink_control *sc)
> >  	if (sc->nr_to_scan) {
> >  		int	dentries;
> >  		int	inodes;
> > +		int	fs_to_scan = 0;
> >  
> >  		/* proportion the scan between the caches */
> >  		dentries = (sc->nr_to_scan * sb->s_nr_dentry_unused) /
> > @@ -87,7 +88,7 @@ static int prune_super(struct shrinker *shrink, struct shrink_control *sc)
> >  		inodes = (sc->nr_to_scan * sb->s_nr_inodes_unused) /
> >  							total_objects;
> >  		if (fs_objects)
> > -			fs_objects = (sc->nr_to_scan * fs_objects) /
> > +			fs_to_scan = (sc->nr_to_scan * fs_objects) /
> >  							total_objects;
> >  		/*
> >  		 * prune the dcache first as the icache is pinned by it, then
> > @@ -96,8 +97,23 @@ static int prune_super(struct shrinker *shrink, struct shrink_control *sc)
> >  		prune_dcache_sb(sb, dentries);
> >  		prune_icache_sb(sb, inodes);
> >  
> > -		if (fs_objects && sb->s_op->free_cached_objects) {
> > -			sb->s_op->free_cached_objects(sb, fs_objects);
> > +		/*
> > +		 * If as a result of pruning the icache, we released some
> > +		 * of the fs_objects, give credit to the fact and
> > +		 * reduce the number of fs objects that we should try
> > +		 * to release.
> > +		 */
> > +		if (fs_to_scan) {
> > +			int fs_objects_now = sb->s_op->nr_cached_objects(sb);
> > +
> > +			if (fs_objects_now < fs_objects)
> > +				fs_to_scan -= fs_objects - fs_objects_now;
> > +			if (fs_to_scan < 0)
> > +				fs_to_scan = 0;
> > +		}
> > +
> > +		if (fs_to_scan && sb->s_op->free_cached_objects) {
> > +			sb->s_op->free_cached_objects(sb, fs_to_scan);
> >  			fs_objects = sb->s_op->nr_cached_objects(sb);
> >  		}
> >  		total_objects = sb->s_nr_dentry_unused +
> > 
> > What do folks think?
> > 
> > 						- Ted
> -- 
> Jan Kara <jack@...e.cz>
> SUSE Labs, CR
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