Patchwork [22/31] libext2fs: During punch, only free a cluster if we're sure that all blocks in the cluster are being punched

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Submitter Darrick J. Wong
Date Oct. 1, 2013, 1:29 a.m.
Message ID <20131001012903.28415.39499.stgit@birch.djwong.org>
Download mbox | patch
Permalink /patch/279301/
State Superseded
Headers show

Comments

Darrick J. Wong - Oct. 1, 2013, 1:29 a.m.
When bigalloc is enabled, using ext2fs_block_alloc_stats2() to free any block
in a cluster has the effect of freeing the entire cluster.  This is problematic
if a caller instructs us to punch, say, blocks 12-15 of a 16-block cluster,
because blocks 0-11 now point to a "free" cluster.

The naive way to solve this problem is to see if any of the other blocks in
this logical cluster map to a physical cluster.  If so, then we know that the
cluster is still in use and it mustn't be freed.  Otherwise, we are punching
the last mapped block in this cluster, so we can free the cluster.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
 lib/ext2fs/bmap.c   |   28 ++++++++++++++++++++++++++++
 lib/ext2fs/ext2fs.h |    3 +++
 lib/ext2fs/punch.c  |   30 +++++++++++++++++++++++++-----
 3 files changed, 56 insertions(+), 5 deletions(-)



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Lukas Czerner - Oct. 10, 2013, 3:53 p.m.
On Mon, 30 Sep 2013, Darrick J. Wong wrote:

> Date: Mon, 30 Sep 2013 18:29:03 -0700
> From: Darrick J. Wong <darrick.wong@oracle.com>
> To: tytso@mit.edu, darrick.wong@oracle.com
> Cc: linux-ext4@vger.kernel.org
> Subject: [PATCH 22/31] libext2fs: During punch,
>     only free a cluster if we're sure that all blocks in the cluster are being
>      punched
> 
> When bigalloc is enabled, using ext2fs_block_alloc_stats2() to free any block
> in a cluster has the effect of freeing the entire cluster.  This is problematic
> if a caller instructs us to punch, say, blocks 12-15 of a 16-block cluster,
> because blocks 0-11 now point to a "free" cluster.
> 
> The naive way to solve this problem is to see if any of the other blocks in
> this logical cluster map to a physical cluster.  If so, then we know that the
> cluster is still in use and it mustn't be freed.  Otherwise, we are punching
> the last mapped block in this cluster, so we can free the cluster.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
>  lib/ext2fs/bmap.c   |   28 ++++++++++++++++++++++++++++
>  lib/ext2fs/ext2fs.h |    3 +++
>  lib/ext2fs/punch.c  |   30 +++++++++++++++++++++++++-----
>  3 files changed, 56 insertions(+), 5 deletions(-)
> 
> 
> diff --git a/lib/ext2fs/bmap.c b/lib/ext2fs/bmap.c
> index 5074587..a6e35a9 100644
> --- a/lib/ext2fs/bmap.c
> +++ b/lib/ext2fs/bmap.c
> @@ -173,6 +173,34 @@ static errcode_t implied_cluster_alloc(ext2_filsys fs, ext2_ino_t ino,
>  	return 0;
>  }
>  
> +errcode_t ext2fs_map_cluster_block(ext2_filsys fs, ext2_ino_t ino,
> +				   struct ext2_inode *inode, blk64_t lblk,
> +				   blk64_t *pblk)
> +{
> +	ext2_extent_handle_t handle;
> +	errcode_t retval;
> +
> +	/* Need bigalloc and extents to be enabled */
> +	*pblk = 0;
> +	if (!EXT2_HAS_RO_COMPAT_FEATURE(fs->super,
> +					EXT4_FEATURE_RO_COMPAT_BIGALLOC) ||
> +	    !(inode->i_flags & EXT4_EXTENTS_FL))
> +		return 0;
> +
> +	retval = ext2fs_extent_open2(fs, ino, inode, &handle);
> +	if (retval)
> +		goto out;
> +
> +	retval = implied_cluster_alloc(fs, ino, inode, handle, lblk, pblk);
> +	if (retval)
> +		goto out2;
> +
> +out2:
> +	ext2fs_extent_free(handle);
> +out:
> +	return retval;
> +}
> +
>  static errcode_t extent_bmap(ext2_filsys fs, ext2_ino_t ino,
>  			     struct ext2_inode *inode,
>  			     ext2_extent_handle_t handle,
> diff --git a/lib/ext2fs/ext2fs.h b/lib/ext2fs/ext2fs.h
> index 9fef6d3..88da8db 100644
> --- a/lib/ext2fs/ext2fs.h
> +++ b/lib/ext2fs/ext2fs.h
> @@ -925,6 +925,9 @@ extern errcode_t ext2fs_bmap2(ext2_filsys fs, ext2_ino_t ino,
>  			      struct ext2_inode *inode,
>  			      char *block_buf, int bmap_flags, blk64_t block,
>  			      int *ret_flags, blk64_t *phys_blk);
> +errcode_t ext2fs_map_cluster_block(ext2_filsys fs, ext2_ino_t ino,
> +				   struct ext2_inode *inode, blk64_t lblk,
> +				   blk64_t *pblk);
>  
>  #if 0
>  /* bmove.c */
> diff --git a/lib/ext2fs/punch.c b/lib/ext2fs/punch.c
> index 4471f46..e0193b0 100644
> --- a/lib/ext2fs/punch.c
> +++ b/lib/ext2fs/punch.c
> @@ -183,8 +183,8 @@ static errcode_t ext2fs_punch_extent(ext2_filsys fs, ext2_ino_t ino,
>  	ext2_extent_handle_t	handle = 0;
>  	struct ext2fs_extent	extent;
>  	errcode_t		retval;
> -	blk64_t			free_start, next;
> -	__u32			free_count, newlen;
> +	blk64_t			free_start, next, lfree_start, pblk;
> +	__u32			free_count, newlen, cluster_freed;
>  	int			freed = 0;
>  	int			op;
>  
> @@ -210,6 +210,7 @@ static errcode_t ext2fs_punch_extent(ext2_filsys fs, ext2_ino_t ino,
>  			/* Start of deleted region before extent; 
>  			   adjust beginning of extent */
>  			free_start = extent.e_pblk;
> +			lfree_start = extent.e_lblk;
>  			if (next > end)
>  				free_count = end - extent.e_lblk + 1;
>  			else
> @@ -225,6 +226,7 @@ static errcode_t ext2fs_punch_extent(ext2_filsys fs, ext2_ino_t ino,
>  			dbg_printf("Case #%d\n", 2);
>  			newlen = start - extent.e_lblk;
>  			free_start = extent.e_pblk + newlen;
> +			lfree_start = extent.e_lblk + newlen;
>  			free_count = extent.e_len - newlen;
>  			extent.e_len = newlen;
>  		} else {
> @@ -240,6 +242,7 @@ static errcode_t ext2fs_punch_extent(ext2_filsys fs, ext2_ino_t ino,
>  
>  			extent.e_len = start - extent.e_lblk;
>  			free_start = extent.e_pblk + extent.e_len;
> +			lfree_start = extent.e_lblk + extent.e_len;
>  			free_count = end - start + 1;
>  
>  			dbg_print_extent("inserting", &newex);
> @@ -280,9 +283,26 @@ static errcode_t ext2fs_punch_extent(ext2_filsys fs, ext2_ino_t ino,
>  			goto errout;
>  		dbg_printf("Free start %llu, free count = %u\n",
>  		       free_start, free_count);
> -		while (free_count-- > 0) {
> -			ext2fs_block_alloc_stats2(fs, free_start++, -1);
> -			freed++;
> +		while (free_count > 0) {
> +			retval = ext2fs_map_cluster_block(fs, ino, inode,
> +							  lfree_start, &pblk);
> +			if (retval)
> +				goto errout;
> +			if (!pblk) {
> +				ext2fs_block_alloc_stats2(fs, free_start, -1);
> +				freed++;
> +				cluster_freed = EXT2FS_CLUSTER_RATIO(fs) -
> +					(free_start & EXT2FS_CLUSTER_MASK(fs));
> +				if (cluster_freed > free_count)
> +					cluster_freed = free_count;
> +				free_count -= cluster_freed;
> +				free_start += cluster_freed;
> +				lfree_start += cluster_freed;
> +				continue;
> +			}
> +			free_count--;
> +			free_start++;
> +			lfree_start++;

I think that this is a little bit excessive. What I think we should
do here is to identify first and last partial cluster and possibly
call ext2fs_map_cluster_block() for those since we might or might
not want to free then depending on whether there are other blocks in
it in-use.

Then just iterate over the whole clusters in between and free them
all. Having to call ext2fs_map_cluster_block() for every single
block we're freeing from the extent tree is not really necessary I think
especially since we really need to get this information for those
possibly partial clusters at the start and end of the extent.

Thanks!
-Lukas


>  		}
>  	next_extent:
>  		retval = ext2fs_extent_get(handle, op,
> 
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Darrick J. Wong - Oct. 10, 2013, 7:29 p.m.
On Thu, Oct 10, 2013 at 05:53:37PM +0200, Lukáš Czerner wrote:
> On Mon, 30 Sep 2013, Darrick J. Wong wrote:
> 
> > Date: Mon, 30 Sep 2013 18:29:03 -0700
> > From: Darrick J. Wong <darrick.wong@oracle.com>
> > To: tytso@mit.edu, darrick.wong@oracle.com
> > Cc: linux-ext4@vger.kernel.org
> > Subject: [PATCH 22/31] libext2fs: During punch,
> >     only free a cluster if we're sure that all blocks in the cluster are being
> >      punched
> > 
> > When bigalloc is enabled, using ext2fs_block_alloc_stats2() to free any block
> > in a cluster has the effect of freeing the entire cluster.  This is problematic
> > if a caller instructs us to punch, say, blocks 12-15 of a 16-block cluster,
> > because blocks 0-11 now point to a "free" cluster.
> > 
> > The naive way to solve this problem is to see if any of the other blocks in
> > this logical cluster map to a physical cluster.  If so, then we know that the
> > cluster is still in use and it mustn't be freed.  Otherwise, we are punching
> > the last mapped block in this cluster, so we can free the cluster.
> > 
> > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> > ---
> >  lib/ext2fs/bmap.c   |   28 ++++++++++++++++++++++++++++
> >  lib/ext2fs/ext2fs.h |    3 +++
> >  lib/ext2fs/punch.c  |   30 +++++++++++++++++++++++++-----
> >  3 files changed, 56 insertions(+), 5 deletions(-)
> > 
> > 
> > diff --git a/lib/ext2fs/bmap.c b/lib/ext2fs/bmap.c
> > index 5074587..a6e35a9 100644
> > --- a/lib/ext2fs/bmap.c
> > +++ b/lib/ext2fs/bmap.c
> > @@ -173,6 +173,34 @@ static errcode_t implied_cluster_alloc(ext2_filsys fs, ext2_ino_t ino,
> >  	return 0;
> >  }
> >  
> > +errcode_t ext2fs_map_cluster_block(ext2_filsys fs, ext2_ino_t ino,
> > +				   struct ext2_inode *inode, blk64_t lblk,
> > +				   blk64_t *pblk)
> > +{
> > +	ext2_extent_handle_t handle;
> > +	errcode_t retval;
> > +
> > +	/* Need bigalloc and extents to be enabled */
> > +	*pblk = 0;
> > +	if (!EXT2_HAS_RO_COMPAT_FEATURE(fs->super,
> > +					EXT4_FEATURE_RO_COMPAT_BIGALLOC) ||
> > +	    !(inode->i_flags & EXT4_EXTENTS_FL))
> > +		return 0;
> > +
> > +	retval = ext2fs_extent_open2(fs, ino, inode, &handle);
> > +	if (retval)
> > +		goto out;
> > +
> > +	retval = implied_cluster_alloc(fs, ino, inode, handle, lblk, pblk);
> > +	if (retval)
> > +		goto out2;
> > +
> > +out2:
> > +	ext2fs_extent_free(handle);
> > +out:
> > +	return retval;
> > +}
> > +
> >  static errcode_t extent_bmap(ext2_filsys fs, ext2_ino_t ino,
> >  			     struct ext2_inode *inode,
> >  			     ext2_extent_handle_t handle,
> > diff --git a/lib/ext2fs/ext2fs.h b/lib/ext2fs/ext2fs.h
> > index 9fef6d3..88da8db 100644
> > --- a/lib/ext2fs/ext2fs.h
> > +++ b/lib/ext2fs/ext2fs.h
> > @@ -925,6 +925,9 @@ extern errcode_t ext2fs_bmap2(ext2_filsys fs, ext2_ino_t ino,
> >  			      struct ext2_inode *inode,
> >  			      char *block_buf, int bmap_flags, blk64_t block,
> >  			      int *ret_flags, blk64_t *phys_blk);
> > +errcode_t ext2fs_map_cluster_block(ext2_filsys fs, ext2_ino_t ino,
> > +				   struct ext2_inode *inode, blk64_t lblk,
> > +				   blk64_t *pblk);
> >  
> >  #if 0
> >  /* bmove.c */
> > diff --git a/lib/ext2fs/punch.c b/lib/ext2fs/punch.c
> > index 4471f46..e0193b0 100644
> > --- a/lib/ext2fs/punch.c
> > +++ b/lib/ext2fs/punch.c
> > @@ -183,8 +183,8 @@ static errcode_t ext2fs_punch_extent(ext2_filsys fs, ext2_ino_t ino,
> >  	ext2_extent_handle_t	handle = 0;
> >  	struct ext2fs_extent	extent;
> >  	errcode_t		retval;
> > -	blk64_t			free_start, next;
> > -	__u32			free_count, newlen;
> > +	blk64_t			free_start, next, lfree_start, pblk;
> > +	__u32			free_count, newlen, cluster_freed;
> >  	int			freed = 0;
> >  	int			op;
> >  
> > @@ -210,6 +210,7 @@ static errcode_t ext2fs_punch_extent(ext2_filsys fs, ext2_ino_t ino,
> >  			/* Start of deleted region before extent; 
> >  			   adjust beginning of extent */
> >  			free_start = extent.e_pblk;
> > +			lfree_start = extent.e_lblk;
> >  			if (next > end)
> >  				free_count = end - extent.e_lblk + 1;
> >  			else
> > @@ -225,6 +226,7 @@ static errcode_t ext2fs_punch_extent(ext2_filsys fs, ext2_ino_t ino,
> >  			dbg_printf("Case #%d\n", 2);
> >  			newlen = start - extent.e_lblk;
> >  			free_start = extent.e_pblk + newlen;
> > +			lfree_start = extent.e_lblk + newlen;
> >  			free_count = extent.e_len - newlen;
> >  			extent.e_len = newlen;
> >  		} else {
> > @@ -240,6 +242,7 @@ static errcode_t ext2fs_punch_extent(ext2_filsys fs, ext2_ino_t ino,
> >  
> >  			extent.e_len = start - extent.e_lblk;
> >  			free_start = extent.e_pblk + extent.e_len;
> > +			lfree_start = extent.e_lblk + extent.e_len;
> >  			free_count = end - start + 1;
> >  
> >  			dbg_print_extent("inserting", &newex);
> > @@ -280,9 +283,26 @@ static errcode_t ext2fs_punch_extent(ext2_filsys fs, ext2_ino_t ino,
> >  			goto errout;
> >  		dbg_printf("Free start %llu, free count = %u\n",
> >  		       free_start, free_count);
> > -		while (free_count-- > 0) {
> > -			ext2fs_block_alloc_stats2(fs, free_start++, -1);
> > -			freed++;
> > +		while (free_count > 0) {
> > +			retval = ext2fs_map_cluster_block(fs, ino, inode,
> > +							  lfree_start, &pblk);
> > +			if (retval)
> > +				goto errout;
> > +			if (!pblk) {
> > +				ext2fs_block_alloc_stats2(fs, free_start, -1);
> > +				freed++;
> > +				cluster_freed = EXT2FS_CLUSTER_RATIO(fs) -
> > +					(free_start & EXT2FS_CLUSTER_MASK(fs));
> > +				if (cluster_freed > free_count)
> > +					cluster_freed = free_count;
> > +				free_count -= cluster_freed;
> > +				free_start += cluster_freed;
> > +				lfree_start += cluster_freed;
> > +				continue;
> > +			}
> > +			free_count--;
> > +			free_start++;
> > +			lfree_start++;
> 
> I think that this is a little bit excessive. What I think we should
> do here is to identify first and last partial cluster and possibly
> call ext2fs_map_cluster_block() for those since we might or might
> not want to free then depending on whether there are other blocks in
> it in-use.
> 
> Then just iterate over the whole clusters in between and free them
> all. Having to call ext2fs_map_cluster_block() for every single
> block we're freeing from the extent tree is not really necessary I think
> especially since we really need to get this information for those
> possibly partial clusters at the start and end of the extent.

Hmm.  I think I could eliminate the middle ext2fs_map_cluster_block() calls by
only calling it if free_start is within cluster_ratio blocks of the pre-loop
value of free_start, or if free_count < cluster_ratio.  I can also split the
whole thing into three loops (pre-cluster, clusters, and post-cluster), though
for the non-bigalloc case I'd skip to the middle loop.

--D
> 
> Thanks!
> -Lukas
> 
> 
> >  		}
> >  	next_extent:
> >  		retval = ext2fs_extent_get(handle, op,
> > 
> > --
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> > the body of a message to majordomo@vger.kernel.org
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> > 
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Patch

diff --git a/lib/ext2fs/bmap.c b/lib/ext2fs/bmap.c
index 5074587..a6e35a9 100644
--- a/lib/ext2fs/bmap.c
+++ b/lib/ext2fs/bmap.c
@@ -173,6 +173,34 @@  static errcode_t implied_cluster_alloc(ext2_filsys fs, ext2_ino_t ino,
 	return 0;
 }
 
+errcode_t ext2fs_map_cluster_block(ext2_filsys fs, ext2_ino_t ino,
+				   struct ext2_inode *inode, blk64_t lblk,
+				   blk64_t *pblk)
+{
+	ext2_extent_handle_t handle;
+	errcode_t retval;
+
+	/* Need bigalloc and extents to be enabled */
+	*pblk = 0;
+	if (!EXT2_HAS_RO_COMPAT_FEATURE(fs->super,
+					EXT4_FEATURE_RO_COMPAT_BIGALLOC) ||
+	    !(inode->i_flags & EXT4_EXTENTS_FL))
+		return 0;
+
+	retval = ext2fs_extent_open2(fs, ino, inode, &handle);
+	if (retval)
+		goto out;
+
+	retval = implied_cluster_alloc(fs, ino, inode, handle, lblk, pblk);
+	if (retval)
+		goto out2;
+
+out2:
+	ext2fs_extent_free(handle);
+out:
+	return retval;
+}
+
 static errcode_t extent_bmap(ext2_filsys fs, ext2_ino_t ino,
 			     struct ext2_inode *inode,
 			     ext2_extent_handle_t handle,
diff --git a/lib/ext2fs/ext2fs.h b/lib/ext2fs/ext2fs.h
index 9fef6d3..88da8db 100644
--- a/lib/ext2fs/ext2fs.h
+++ b/lib/ext2fs/ext2fs.h
@@ -925,6 +925,9 @@  extern errcode_t ext2fs_bmap2(ext2_filsys fs, ext2_ino_t ino,
 			      struct ext2_inode *inode,
 			      char *block_buf, int bmap_flags, blk64_t block,
 			      int *ret_flags, blk64_t *phys_blk);
+errcode_t ext2fs_map_cluster_block(ext2_filsys fs, ext2_ino_t ino,
+				   struct ext2_inode *inode, blk64_t lblk,
+				   blk64_t *pblk);
 
 #if 0
 /* bmove.c */
diff --git a/lib/ext2fs/punch.c b/lib/ext2fs/punch.c
index 4471f46..e0193b0 100644
--- a/lib/ext2fs/punch.c
+++ b/lib/ext2fs/punch.c
@@ -183,8 +183,8 @@  static errcode_t ext2fs_punch_extent(ext2_filsys fs, ext2_ino_t ino,
 	ext2_extent_handle_t	handle = 0;
 	struct ext2fs_extent	extent;
 	errcode_t		retval;
-	blk64_t			free_start, next;
-	__u32			free_count, newlen;
+	blk64_t			free_start, next, lfree_start, pblk;
+	__u32			free_count, newlen, cluster_freed;
 	int			freed = 0;
 	int			op;
 
@@ -210,6 +210,7 @@  static errcode_t ext2fs_punch_extent(ext2_filsys fs, ext2_ino_t ino,
 			/* Start of deleted region before extent; 
 			   adjust beginning of extent */
 			free_start = extent.e_pblk;
+			lfree_start = extent.e_lblk;
 			if (next > end)
 				free_count = end - extent.e_lblk + 1;
 			else
@@ -225,6 +226,7 @@  static errcode_t ext2fs_punch_extent(ext2_filsys fs, ext2_ino_t ino,
 			dbg_printf("Case #%d\n", 2);
 			newlen = start - extent.e_lblk;
 			free_start = extent.e_pblk + newlen;
+			lfree_start = extent.e_lblk + newlen;
 			free_count = extent.e_len - newlen;
 			extent.e_len = newlen;
 		} else {
@@ -240,6 +242,7 @@  static errcode_t ext2fs_punch_extent(ext2_filsys fs, ext2_ino_t ino,
 
 			extent.e_len = start - extent.e_lblk;
 			free_start = extent.e_pblk + extent.e_len;
+			lfree_start = extent.e_lblk + extent.e_len;
 			free_count = end - start + 1;
 
 			dbg_print_extent("inserting", &newex);
@@ -280,9 +283,26 @@  static errcode_t ext2fs_punch_extent(ext2_filsys fs, ext2_ino_t ino,
 			goto errout;
 		dbg_printf("Free start %llu, free count = %u\n",
 		       free_start, free_count);
-		while (free_count-- > 0) {
-			ext2fs_block_alloc_stats2(fs, free_start++, -1);
-			freed++;
+		while (free_count > 0) {
+			retval = ext2fs_map_cluster_block(fs, ino, inode,
+							  lfree_start, &pblk);
+			if (retval)
+				goto errout;
+			if (!pblk) {
+				ext2fs_block_alloc_stats2(fs, free_start, -1);
+				freed++;
+				cluster_freed = EXT2FS_CLUSTER_RATIO(fs) -
+					(free_start & EXT2FS_CLUSTER_MASK(fs));
+				if (cluster_freed > free_count)
+					cluster_freed = free_count;
+				free_count -= cluster_freed;
+				free_start += cluster_freed;
+				lfree_start += cluster_freed;
+				continue;
+			}
+			free_count--;
+			free_start++;
+			lfree_start++;
 		}
 	next_extent:
 		retval = ext2fs_extent_get(handle, op,