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Date: Mon, 25 Nov 2013 16:51:49 +0800
From: Zheng Liu <gnehzuil.liu@...il.com>
To: "Darrick J. Wong" <darrick.wong@...cle.com>
Cc: tytso@....edu, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 11/25] libext2fs: only punch complete clusters
On Thu, Oct 17, 2013 at 09:50:08PM -0700, Darrick J. Wong wrote:
> 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.
>
> The implementation given only does the rigorous checks for the partial
> clusters at the beginning and end of the punching range.
>
> v2: Refactor the block free code into a separate helper function that
> should be more efficient.
>
> Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
Reviewed-by: Zheng Liu <wenqing.lz@...bao.com>
- Zheng
> ---
> lib/ext2fs/bmap.c | 29 ++++++++++++++++++
> lib/ext2fs/ext2fs.h | 3 ++
> lib/ext2fs/punch.c | 82 ++++++++++++++++++++++++++++++++++++++++++++++++---
> 3 files changed, 109 insertions(+), 5 deletions(-)
>
>
> diff --git a/lib/ext2fs/bmap.c b/lib/ext2fs/bmap.c
> index 5074587..80f8f86 100644
> --- a/lib/ext2fs/bmap.c
> +++ b/lib/ext2fs/bmap.c
> @@ -173,6 +173,35 @@ static errcode_t implied_cluster_alloc(ext2_filsys fs, ext2_ino_t ino,
> return 0;
> }
>
> +/* Try to map a logical block to an already-allocated physical cluster. */
> +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 8f82dae..5247922 100644
> --- a/lib/ext2fs/ext2fs.h
> +++ b/lib/ext2fs/ext2fs.h
> @@ -924,6 +924,9 @@ 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 790a0ad8..1e4398e 100644
> --- a/lib/ext2fs/punch.c
> +++ b/lib/ext2fs/punch.c
> @@ -177,6 +177,75 @@ static void dbg_print_extent(char *desc, struct ext2fs_extent *extent)
> #define dbg_printf(f, a...) do { } while (0)
> #endif
>
> +/* Free a range of blocks, respecting cluster boundaries */
> +static errcode_t punch_extent_blocks(ext2_filsys fs, ext2_ino_t ino,
> + struct ext2_inode *inode,
> + blk64_t lfree_start, blk64_t free_start,
> + __u32 free_count, int *freed)
> +{
> + blk64_t pblk;
> + int freed_now = 0;
> + __u32 cluster_freed;
> + errcode_t retval = 0;
> +
> + /* No bigalloc? Just free each block. */
> + if (EXT2FS_CLUSTER_RATIO(fs) == 1) {
> + *freed += free_count;
> + while (free_count-- > 0)
> + ext2fs_block_alloc_stats2(fs, free_start++, -1);
> + return retval;
> + }
> +
> + /*
> + * Try to free up to the next cluster boundary. We assume that all
> + * blocks in a logical cluster map to blocks from the same physical
> + * cluster, and that the offsets within the [pl]clusters match.
> + */
> + if (free_start & EXT2FS_CLUSTER_MASK(fs)) {
> + 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_now++;
> + }
> + 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;
> + }
> +
> + /* Free whole clusters from the middle of the range. */
> + while (free_count > 0 && free_count >= EXT2FS_CLUSTER_RATIO(fs)) {
> + ext2fs_block_alloc_stats2(fs, free_start, -1);
> + freed_now++;
> + cluster_freed = EXT2FS_CLUSTER_RATIO(fs);
> + free_count -= cluster_freed;
> + free_start += cluster_freed;
> + lfree_start += cluster_freed;
> + }
> +
> + /* Try to free the last cluster. */
> + if (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_now++;
> + }
> + }
> +
> +errout:
> + *freed += freed_now;
> + return retval;
> +}
> +
> static errcode_t ext2fs_punch_extent(ext2_filsys fs, ext2_ino_t ino,
> struct ext2_inode *inode,
> blk64_t start, blk64_t end)
> @@ -184,7 +253,7 @@ 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;
> + blk64_t free_start, next, lfree_start;
> __u32 free_count, newlen;
> int freed = 0;
> int op;
> @@ -211,6 +280,7 @@ 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
> @@ -226,6 +296,7 @@ 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 {
> @@ -241,6 +312,7 @@ 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);
> @@ -281,10 +353,10 @@ 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++;
> - }
> + retval = punch_extent_blocks(fs, ino, inode, lfree_start,
> + free_start, free_count, &freed);
> + if (retval)
> + goto errout;
> next_extent:
> retval = ext2fs_extent_get(handle, op,
> &extent);
>
> --
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