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Date: Sat, 14 Oct 2023 18:09:28 -0700
From: Joel Becker <jlbec@...lplan.org>
To: Seamus Connor <sconnor@...estorage.com>
Cc: Christoph Hellwig <hch@....de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] configfs: improve item creation performance
On Fri, Oct 13, 2023 at 02:11:29PM -0700, Seamus Connor wrote:
> As the size of a directory increases item creation slows down.
> Optimizing access to s_children removes this bottleneck.
>
> dirents are already pinned into the cache, there is no need to scan the
> s_children list looking for duplicate Items. The configfs_dirent_exists
> check is moved to a location where it is called only during subsystem
> initialization.
>
> d_lookup will only need to call configfs_lookup in the case where the
> item in question is not pinned to dcache. The only items not pinned to
> dcache are attributes. These are placed at the front of the s_children
> list, whilst pinned items are inserted at the back. configfs_lookup
> stops scanning when it encounters the first pinned entry in s_children.
>
> The assumption of the above optimizations is that there will be few
> attributes, but potentially many Items in a given directory.
>
> Signed-off-by: Seamus Connor <sconnor@...estorage.com>
> Cc: Joel Becker <jlbec@...lplan.org>
> Cc: Christoph Hellwig <hch@....de>
> Cc: linux-kernel@...r.kernel.org
Reviewed-by: Joel Becker <jlbec@...lplan.org>
> ---
>
> In this revision I've added some commentary describing the changes, and
> I have removed a helper function.
>
> fs/configfs/configfs_internal.h | 3 +--
> fs/configfs/dir.c | 39 +++++++++++++++++++++++++--------
> fs/configfs/inode.c | 24 --------------------
> 3 files changed, 31 insertions(+), 35 deletions(-)
>
> diff --git a/fs/configfs/configfs_internal.h b/fs/configfs/configfs_internal.h
> index c0395363eab9..b91036fd71b1 100644
> --- a/fs/configfs/configfs_internal.h
> +++ b/fs/configfs/configfs_internal.h
> @@ -55,6 +55,7 @@ struct configfs_dirent {
> #define CONFIGFS_USET_IN_MKDIR 0x0200
> #define CONFIGFS_USET_CREATING 0x0400
> #define CONFIGFS_NOT_PINNED (CONFIGFS_ITEM_ATTR | CONFIGFS_ITEM_BIN_ATTR)
> +#define CONFIGFS_PINNED (CONFIGFS_ROOT | CONFIGFS_DIR | CONFIGFS_ITEM_LINK)
>
> extern struct mutex configfs_symlink_mutex;
> extern spinlock_t configfs_dirent_lock;
> @@ -73,8 +74,6 @@ extern int configfs_make_dirent(struct configfs_dirent *, struct dentry *,
> void *, umode_t, int, struct configfs_fragment *);
> extern int configfs_dirent_is_ready(struct configfs_dirent *);
>
> -extern void configfs_hash_and_remove(struct dentry * dir, const char * name);
> -
> extern const unsigned char * configfs_get_name(struct configfs_dirent *sd);
> extern void configfs_drop_dentry(struct configfs_dirent *sd, struct dentry *parent);
> extern int configfs_setattr(struct user_namespace *mnt_userns,
> diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c
> index d1f9d2632202..64a0eac83b90 100644
> --- a/fs/configfs/dir.c
> +++ b/fs/configfs/dir.c
> @@ -207,7 +207,17 @@ static struct configfs_dirent *configfs_new_dirent(struct configfs_dirent *paren
> return ERR_PTR(-ENOENT);
> }
> sd->s_frag = get_fragment(frag);
> - list_add(&sd->s_sibling, &parent_sd->s_children);
> +
> + /*
> + * configfs_lookup scans only for unpinned items. s_children is
> + * partitioned so that configfs_lookup can bail out early.
> + * CONFIGFS_PINNED and CONFIGFS_NOT_PINNED are not symmetrical. readdir
> + * cursors still need to be inserted at the front of the list.
> + */
> + if (sd->s_type & CONFIGFS_PINNED)
> + list_add_tail(&sd->s_sibling, &parent_sd->s_children);
> + else
> + list_add(&sd->s_sibling, &parent_sd->s_children);
> spin_unlock(&configfs_dirent_lock);
>
> return sd;
> @@ -220,10 +230,11 @@ static struct configfs_dirent *configfs_new_dirent(struct configfs_dirent *paren
> *
> * called with parent inode's i_mutex held
> */
> -static int configfs_dirent_exists(struct configfs_dirent *parent_sd,
> - const unsigned char *new)
> +static int configfs_dirent_exists(struct dentry *dentry)
> {
> - struct configfs_dirent * sd;
> + struct configfs_dirent *parent_sd = dentry->d_parent->d_fsdata;
> + const unsigned char *new = dentry->d_name.name;
> + struct configfs_dirent *sd;
>
> list_for_each_entry(sd, &parent_sd->s_children, s_sibling) {
> if (sd->s_element) {
> @@ -289,10 +300,6 @@ static int configfs_create_dir(struct config_item *item, struct dentry *dentry,
>
> BUG_ON(!item);
>
> - error = configfs_dirent_exists(p->d_fsdata, dentry->d_name.name);
> - if (unlikely(error))
> - return error;
> -
> error = configfs_make_dirent(p->d_fsdata, dentry, item, mode,
> CONFIGFS_DIR | CONFIGFS_USET_CREATING,
> frag);
> @@ -449,6 +456,18 @@ static struct dentry * configfs_lookup(struct inode *dir,
>
> spin_lock(&configfs_dirent_lock);
> list_for_each_entry(sd, &parent_sd->s_children, s_sibling) {
> +
> + /*
> + * s_children is partitioned, see configfs_new_dirent. The first
> + * pinned item indicates we can stop scanning.
> + */
> + if (sd->s_type & CONFIGFS_PINNED)
> + break;
> +
> + /*
> + * Note: CONFIGFS_PINNED and CONFIGFS_NOT_PINNED are asymmetric.
> + * there may be a readdir cursor in this list
> + */
> if ((sd->s_type & CONFIGFS_NOT_PINNED) &&
> !strcmp(configfs_get_name(sd), dentry->d_name.name)) {
> struct configfs_attribute *attr = sd->s_element;
> @@ -1878,7 +1897,9 @@ int configfs_register_subsystem(struct configfs_subsystem *subsys)
> if (dentry) {
> d_add(dentry, NULL);
>
> - err = configfs_attach_group(sd->s_element, &group->cg_item,
> + err = configfs_dirent_exists(dentry);
> + if (!err)
> + err = configfs_attach_group(sd->s_element, &group->cg_item,
> dentry, frag);
> if (err) {
> BUG_ON(d_inode(dentry));
> diff --git a/fs/configfs/inode.c b/fs/configfs/inode.c
> index b601610e9907..15964e62329d 100644
> --- a/fs/configfs/inode.c
> +++ b/fs/configfs/inode.c
> @@ -218,27 +218,3 @@ void configfs_drop_dentry(struct configfs_dirent * sd, struct dentry * parent)
> }
> }
>
> -void configfs_hash_and_remove(struct dentry * dir, const char * name)
> -{
> - struct configfs_dirent * sd;
> - struct configfs_dirent * parent_sd = dir->d_fsdata;
> -
> - if (d_really_is_negative(dir))
> - /* no inode means this hasn't been made visible yet */
> - return;
> -
> - inode_lock(d_inode(dir));
> - list_for_each_entry(sd, &parent_sd->s_children, s_sibling) {
> - if (!sd->s_element)
> - continue;
> - if (!strcmp(configfs_get_name(sd), name)) {
> - spin_lock(&configfs_dirent_lock);
> - list_del_init(&sd->s_sibling);
> - spin_unlock(&configfs_dirent_lock);
> - configfs_drop_dentry(sd, dir);
> - configfs_put(sd);
> - break;
> - }
> - }
> - inode_unlock(d_inode(dir));
> -}
> --
> 2.37.0
>
--
"Glory is fleeting, but obscurity is forever."
- Napoleon Bonaparte
http://www.jlbec.org/
jlbec@...lplan.org
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