linux-kernel - Re: [PATCH 6/6] btrfs: check mergeable free space when removing a cluster

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Message-ID: <20100824025847.GB2638@dhcp231-156.rdu.redhat.com>
Date:	Mon, 23 Aug 2010 22:58:47 -0400
From:	Josef Bacik <josef@...hat.com>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	Josef Bacik <josef@...hat.com>,
	Chris Mason <chris.mason@...cle.com>,
	linux-btrfs@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 6/6] btrfs: check mergeable free space when removing a
	cluster

On Tue, Aug 24, 2010 at 09:04:13AM +0800, Li Zefan wrote:
> Josef Bacik wrote:
> > On Mon, Aug 23, 2010 at 09:24:07AM +0800, Li Zefan wrote:
> >> After returing extents from a cluster to the block group, some
> >> extents in the block group may be mergeable.
> >>
> >> Signed-off-by: Li Zefan <lizf@...fujitsu.com>
> >> ---
> >>  fs/btrfs/free-space-cache.c |   26 ++++++++++++++++++++------
> >>  1 files changed, 20 insertions(+), 6 deletions(-)
> >>
> >> diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
> >> index faeec8f..c11f4f7 100644
> >> --- a/fs/btrfs/free-space-cache.c
> >> +++ b/fs/btrfs/free-space-cache.c
> >> @@ -234,11 +234,18 @@ tree_search_offset(struct btrfs_block_group_cache *block_group,
> >>  	return entry;
> >>  }
> >>  
> >> -static void unlink_free_space(struct btrfs_block_group_cache *block_group,
> >> -			      struct btrfs_free_space *info)
> >> +static inline void
> >> +__unlink_free_space(struct btrfs_block_group_cache *block_group,
> >> +		    struct btrfs_free_space *info)
> >>  {
> >>  	rb_erase(&info->offset_index, &block_group->free_space_offset);
> >>  	block_group->free_extents--;
> >> +}
> >> +
> >> +static void unlink_free_space(struct btrfs_block_group_cache *block_group,
> >> +			      struct btrfs_free_space *info)
> >> +{
> >> +	__unlink_free_space(block_group, info);
> >>  	block_group->free_space -= info->bytes;
> >>  }
> >>  
> >> @@ -611,7 +618,7 @@ out:
> >>  }
> >>  
> >>  bool try_merge_free_space(struct btrfs_block_group_cache *block_group,
> >> -			  struct btrfs_free_space *info)
> >> +			  struct btrfs_free_space *info, bool update_stat)
> >>  {
> >>  	struct btrfs_free_space *left_info;
> >>  	struct btrfs_free_space *right_info;
> >> @@ -632,7 +639,10 @@ bool try_merge_free_space(struct btrfs_block_group_cache *block_group,
> >>  		left_info = tree_search_offset(block_group, offset - 1, 0, 0);
> >>  
> >>  	if (right_info && !right_info->bitmap) {
> >> -		unlink_free_space(block_group, right_info);
> >> +		if (update_stat)
> >> +			unlink_free_space(block_group, right_info);
> >> +		else
> >> +			__unlink_free_space(block_group, right_info);
> >>  		info->bytes += right_info->bytes;
> >>  		kfree(right_info);
> >>  		merged = true;
> >> @@ -640,7 +650,10 @@ bool try_merge_free_space(struct btrfs_block_group_cache *block_group,
> >>  
> >>  	if (left_info && !left_info->bitmap &&
> >>  	    left_info->offset + left_info->bytes == offset) {
> >> -		unlink_free_space(block_group, left_info);
> >> +		if (update_stat)
> >> +			unlink_free_space(block_group, left_info);
> >> +		else
> >> +			__unlink_free_space(block_group, left_info);
> >>  		info->offset = left_info->offset;
> >>  		info->bytes += left_info->bytes;
> >>  		kfree(left_info);
> >> @@ -665,7 +678,7 @@ int btrfs_add_free_space(struct btrfs_block_group_cache *block_group,
> >>  
> >>  	spin_lock(&block_group->tree_lock);
> >>  
> >> -	if (try_merge_free_space(block_group, info))
> >> +	if (try_merge_free_space(block_group, info, true))
> >>  		goto link;
> >>  
> >>  	/*
> >> @@ -883,6 +896,7 @@ __btrfs_return_cluster_to_free_space(
> >>  		node = rb_next(&entry->offset_index);
> >>  		rb_erase(&entry->offset_index, &cluster->root);
> >>  		BUG_ON(entry->bitmap);
> >> +		try_merge_free_space(block_group, entry, false);
> >>  		tree_insert_offset(&block_group->free_space_offset,
> >>  				   entry->offset, &entry->offset_index, 0);
> > 
> > It's early in the morning here, so forgive me if I'm missing something obvious,
> > but if try_merge_free_space() succeeds here, then won't tree_insert_offset()
> > then add an entry that overlaps the same spot?  Should we do something like
> > 
> > merged = try_merge_free_space();
> > if (!merged)
> > 	tree_insert_offset();
> > 
> > ?  Thanks,
> > 
> 
> In try_merge_free_space() we try to merge the left and right entry into
> @entry, and then the caller has to insert the @entry into the tree by
> itself.
> 
> Similarly, In btrfs_add_free_space() we call link_free_space() no matter
> try_merge_free_space() returns success or not.

Ah ok I see now, thanks.

Reviewed-by: Josef Bacik <josef@...hat.com>

Thanks,

Josef
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