linux-ext4 - Re: [PATCH -v2] ext4: use truncate

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Date:	Mon, 23 May 2011 13:22:38 -0700
From:	Jiaying Zhang <jiayingz@...gle.com>
To:	"Theodore Ts'o" <tytso@....edu>
Cc:	Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH -v2] ext4: use truncate_setsize() unconditionally

On Mon, May 23, 2011 at 12:19 PM, Theodore Ts'o <tytso@....edu> wrote:
> In commit c8d46e41 (ext4: Add flag to files with blocks intentionally
> past EOF), if the EOFBLOCKS_FL flag is set, we call ext4_truncate()
> before calling vmtruncate().  This caused any allocated but unwritten
> blocks created by calling fallocate() with the FALLOC_FL_KEEP_SIZE
> flag to be dropped.  This was done to make to make sure that
> EOFBLOCKS_FL would not be cleared while still leaving blocks past
> i_size allocated.  This was not necessary, since ext4_truncate()
> guarantees that blocks past i_size will be dropped, even in the case
> where truncate() has increased i_size before calling ext4_truncate().
>
> So fix this by removing the EOFBLOCKS_FL special case treatment in
> ext4_setattr().  In addition, use truncate_setsize() followed by a
> call to ext4_truncate() instead of using vmtruncate().  This is more
> efficient since it skips the call to inode_newsize_ok(), which has
> been checked already by inode_change_ok().  This is also in a win in
> the case where EOFBLOCKS_FL is set since it avoids calling
> ext4_truncate() twice.
>
> Signed-off-by: "Theodore Ts'o" <tytso@....edu>
> ---
>  Jiayingz pointed out that in the case where we fallocate 12k, write 4k, and
>  then truncate to 4k, we should discard the excess fallocate'd blocks.  So if
>  attr->ia_size == inode.i_size, we can skip the truncate_setsize() call, but
>  if the EOFBLOCKS_FL flag is set, we should still call ext4_truncate().
>
>  fs/ext4/inode.c |   16 ++++++++--------
>  1 files changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index df3fb20..2e95819 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -5363,8 +5363,7 @@ int ext4_setattr(struct dentry *dentry, struct iattr *attr)
>
>        if (S_ISREG(inode->i_mode) &&
>            attr->ia_valid & ATTR_SIZE &&
> -           (attr->ia_size < inode->i_size ||
> -            (ext4_test_inode_flag(inode, EXT4_INODE_EOFBLOCKS)))) {
> +           (attr->ia_size < inode->i_size)) {
>                handle_t *handle;
>
>                handle = ext4_journal_start(inode, 3);
> @@ -5398,14 +5397,15 @@ int ext4_setattr(struct dentry *dentry, struct iattr *attr)
>                                goto err_out;
>                        }
>                }
> -               /* ext4_truncate will clear the flag */
> -               if ((ext4_test_inode_flag(inode, EXT4_INODE_EOFBLOCKS)))
> -                       ext4_truncate(inode);
>        }
>
> -       if ((attr->ia_valid & ATTR_SIZE) &&
> -           attr->ia_size != i_size_read(inode))
> -               rc = vmtruncate(inode, attr->ia_size);
> +       if (attr->ia_valid & ATTR_SIZE) {
> +               if (attr->ia_size != i_size_read(inode)) {
> +                       truncate_setsize(inode, attr->ia_size);
> +                       ext4_truncate(inode);
> +               } else if (ext4_test_inode_flag(inode, EXT4_INODE_EOFBLOCKS))
> +                       ext4_truncate(inode);
> +       }
>
>        if (!rc) {
>                setattr_copy(inode, attr);
> --
> 1.7.3.1
lgtm.

Jiaying

>
>
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