On Thu, Jan 25, 2018 at 10:58 AM, Hou Tao <houtao1@xxxxxxxxxx> wrote:
> Now each whiteout file will be assigned a new inode. To reduce the
> overhead of allocating and freeing inodes in upper fs, creating a
> whiteout file under workbasedir and hardlink all whiteout files into it.
>
> The effect is obvious: under my VM, the time used for removing the
> linux kernel source tree will be reduced from 17s to 10s.
>
> Got the idea from autofs.
Yep, this was talked about, then forgotten. Thanks for bringing it up.
The implementation is a little more difficult though, because there's
a limit to how many hard links to a single file are allowed.
So it should be something like:
- try hard linking "singleton", if succeeds then fine
- else unlink old singleton from workdir, create new one and use that one
If it's possible to get a filesystem as upper that doesn't support
hard links at all, then that also needs to be taken care of, to fall
back to non-hard linked whiteouts.
Thanks,
Miklos
>
> Signed-off-by: Hou Tao <houtao1@xxxxxxxxxx>
> ---
> fs/overlayfs/dir.c | 13 +++++++++++-
> fs/overlayfs/ovl_entry.h | 5 +++++
> fs/overlayfs/super.c | 52 +++++++++++++++++++++++++++++++++++++++++++++++-
> 3 files changed, 68 insertions(+), 2 deletions(-)
>
> diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
> index f9788bc..ef02477 100644
> --- a/fs/overlayfs/dir.c
> +++ b/fs/overlayfs/dir.c
> @@ -62,11 +62,19 @@ struct dentry *ovl_lookup_temp(struct dentry *workdir)
> return temp;
> }
>
> +static inline struct dentry *ovl_singleton_whiteout(struct dentry *dentry)
> +{
> + struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
> +
> + return ofs->whiteout;
> +}
> +
> /* caller holds i_mutex on workdir */
> static struct dentry *ovl_whiteout(struct dentry *workdir,
> struct dentry *dentry)
> {
> int err;
> + struct dentry *singleton = ovl_singleton_whiteout(dentry);
> struct dentry *whiteout;
> struct inode *wdir = workdir->d_inode;
>
> @@ -74,7 +82,10 @@ static struct dentry *ovl_whiteout(struct dentry *workdir,
> if (IS_ERR(whiteout))
> return whiteout;
>
> - err = ovl_do_whiteout(wdir, whiteout);
> + if (singleton)
> + err = ovl_do_link(singleton, wdir, whiteout, false);
> + else
> + err = ovl_do_whiteout(wdir, whiteout);
> if (err) {
> dput(whiteout);
> whiteout = ERR_PTR(err);
> diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
> index 9d0bc03..c435538 100644
> --- a/fs/overlayfs/ovl_entry.h
> +++ b/fs/overlayfs/ovl_entry.h
> @@ -40,6 +40,11 @@ struct ovl_fs {
> struct dentry *workdir;
> /* index directory listing overlay inodes by origin file handle */
> struct dentry *indexdir;
> + /*
> + * the singleton whiteout file under workbasedir
> + * all newly created whiteout files will be linked to it
> + */
> + struct dentry *whiteout;
> long namelen;
> /* pathnames of lower and upper dirs, for show_options */
> struct ovl_config config;
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index 76440fe..16a7d7f 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -223,6 +223,7 @@ static void ovl_free_fs(struct ovl_fs *ofs)
> unsigned i;
>
> dput(ofs->indexdir);
> + dput(ofs->whiteout);
> dput(ofs->workdir);
> if (ofs->workdir_locked)
> ovl_inuse_unlock(ofs->workbasedir);
> @@ -509,6 +510,7 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config)
>
> #define OVL_WORKDIR_NAME "work"
> #define OVL_INDEXDIR_NAME "index"
> +#define OVL_WHITEOUT_FILE_NAME "whiteout"
>
> static struct dentry *ovl_workdir_create(struct ovl_fs *ofs,
> const char *name, bool persist)
> @@ -1023,6 +1025,48 @@ static int ovl_get_workdir(struct ovl_fs *ofs, struct path *upperpath)
> return err;
> }
>
> +/*
> + * create a new whiteout file under workbasedir if it doesn't exist.
> + * If a non-whiteout file has existed, the singleton whiteout will
> + * not be created.
> + */
> +static int ovl_make_singleton_whiteout(struct ovl_fs *ofs, const char *name)
> +{
> + int err = 0;
> + struct vfsmount *mnt = ofs->upper_mnt;
> + struct inode *dir = d_inode(ofs->workbasedir);
> + struct dentry *whiteout;
> +
> + err = mnt_want_write(mnt);
> + if (err)
> + return err;
> +
> + inode_lock_nested(dir, I_MUTEX_PARENT);
> +
> + whiteout = lookup_one_len(name, ofs->workbasedir, strlen(name));
> + if (!IS_ERR(whiteout)) {
> + if (ovl_is_whiteout(whiteout)) {
> + ofs->whiteout = whiteout;
> + } else if (!whiteout->d_inode) {
> + err = ovl_do_whiteout(dir, whiteout);
> + if (!err)
> + ofs->whiteout = whiteout;
> + else
> + dput(whiteout);
> + } else {
> + dput(whiteout);
> + ofs->whiteout = NULL;
> + }
> + } else {
> + err = PTR_ERR(whiteout);
> + }
> +
> + inode_unlock(dir);
> + mnt_drop_write(mnt);
> +
> + return err;
> +}
> +
> static int ovl_get_indexdir(struct ovl_fs *ofs, struct ovl_entry *oe,
> struct path *upperpath)
> {
> @@ -1234,8 +1278,14 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
> if (err)
> goto out_err;
>
> - if (!ofs->workdir)
> + if (ofs->workdir) {
> + err = ovl_make_singleton_whiteout(ofs,
> + OVL_WHITEOUT_FILE_NAME);
> + if (err)
> + goto out_err;
> + } else {
> sb->s_flags |= SB_RDONLY;
> + }
>
> sb->s_stack_depth = ofs->upper_mnt->mnt_sb->s_stack_depth;
> sb->s_time_gran = ofs->upper_mnt->mnt_sb->s_time_gran;
> --
> 2.9.5
>
--
To unsubscribe from this list: send the line "unsubscribe linux-unionfs" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
