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Message-ID: <20170719074056.GA12546@quack2.suse.cz>
Date: Wed, 19 Jul 2017 09:40:56 +0200
From: Jan Kara <jack@...e.cz>
To: Davidlohr Bueso <dave@...olabs.net>
Cc: akpm@...ux-foundation.org, mingo@...nel.org, peterz@...radead.org,
jack@...e.cz, torvalds@...ux-foundation.org,
kirill.shutemov@...ux.intel.com, hch@...radead.org,
ldufour@...ux.vnet.ibm.com, mhocko@...e.com,
mgorman@...hsingularity.net, linux-kernel@...r.kernel.org,
tytso@....edu, Davidlohr Bueso <dbueso@...e.de>
Subject: Re: [PATCH 15/17] fs/ext4: use cached rbtrees
On Tue 18-07-17 18:46:01, Davidlohr Bueso wrote:
> This patch replaces two uses of rbtrees to the cached version for
> better rb_first() performance during:
>
> * Tree traversals to mark blocks as used during ext4_mb_init_cache()
> looping. (struct ext4_group_info)
>
> * Storing ->curr_node for dx_readdir(). (struct dir_private_info)
>
> Caching the leftmost node comes at negligible runtime cost, thus the
> only downside is that the aforementioned structures are enlarged for
> the extra pointer. No changes in semantics whatsoever.
>
> Cc: tytso@....edu
> Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
Hum, so I'm somewhat undecided whether this is worth the churn. For free
blocks rb_tree we use rb_first() only in ext4_mb_generate_from_freelist()
which gets called only when generating new buddy bitmap from on-disk bitmap
and we traverse the whole tree after that - thus the extra cost of
rb_first() is a) well hidden in the total cost of iteration, b) rather rare
anyway.
Similarly for the H-tree directory code, we call rb_first() in
ext4_dx_readdir() only to start an iteration over the whole B-tree and in
such case I don't think optimizing rb_first() makes a big difference
(maintaining cached value is going to have about the same cost as we save
by using it).
Honza
> ---
> This is part of the rbtree internal caching series:
> https://lwn.net/Articles/726809/
>
> fs/ext4/dir.c | 24 ++++++++++++++----------
> fs/ext4/ext4.h | 4 ++--
> fs/ext4/mballoc.c | 22 ++++++++++++----------
> 3 files changed, 28 insertions(+), 22 deletions(-)
>
> diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c
> index e8b365000d73..011df6bba13c 100644
> --- a/fs/ext4/dir.c
> +++ b/fs/ext4/dir.c
> @@ -391,18 +391,18 @@ struct fname {
> * This functoin implements a non-recursive way of freeing all of the
> * nodes in the red-black tree.
> */
> -static void free_rb_tree_fname(struct rb_root *root)
> +static void free_rb_tree_fname(struct rb_root_cached *root)
> {
> struct fname *fname, *next;
>
> - rbtree_postorder_for_each_entry_safe(fname, next, root, rb_hash)
> + rbtree_postorder_for_each_entry_safe(fname, next, &root->rb_root, rb_hash)
> while (fname) {
> struct fname *old = fname;
> fname = fname->next;
> kfree(old);
> }
>
> - *root = RB_ROOT;
> + *root = RB_ROOT_CACHED;
> }
>
>
> @@ -441,9 +441,10 @@ int ext4_htree_store_dirent(struct file *dir_file, __u32 hash,
> struct fname *fname, *new_fn;
> struct dir_private_info *info;
> int len;
> + bool leftmost = true;
>
> info = dir_file->private_data;
> - p = &info->root.rb_node;
> + p = &info->root.rb_root.rb_node;
>
> /* Create and allocate the fname structure */
> len = sizeof(struct fname) + ent_name->len + 1;
> @@ -475,16 +476,19 @@ int ext4_htree_store_dirent(struct file *dir_file, __u32 hash,
>
> if (new_fn->hash < fname->hash)
> p = &(*p)->rb_left;
> - else if (new_fn->hash > fname->hash)
> + else if (new_fn->hash > fname->hash) {
> p = &(*p)->rb_right;
> - else if (new_fn->minor_hash < fname->minor_hash)
> + leftmost = false;
> + } else if (new_fn->minor_hash < fname->minor_hash)
> p = &(*p)->rb_left;
> - else /* if (new_fn->minor_hash > fname->minor_hash) */
> + else { /* if (new_fn->minor_hash > fname->minor_hash) */
> p = &(*p)->rb_right;
> + leftmost = false;
> + }
> }
>
> rb_link_node(&new_fn->rb_hash, parent, p);
> - rb_insert_color(&new_fn->rb_hash, &info->root);
> + rb_insert_color_cached(&new_fn->rb_hash, &info->root, leftmost);
> return 0;
> }
>
> @@ -558,7 +562,7 @@ static int ext4_dx_readdir(struct file *file, struct dir_context *ctx)
> info->extra_fname = NULL;
> goto next_node;
> } else if (!info->curr_node)
> - info->curr_node = rb_first(&info->root);
> + info->curr_node = rb_first_cached(&info->root);
>
> while (1) {
> /*
> @@ -580,7 +584,7 @@ static int ext4_dx_readdir(struct file *file, struct dir_context *ctx)
> ctx->pos = ext4_get_htree_eof(file);
> break;
> }
> - info->curr_node = rb_first(&info->root);
> + info->curr_node = rb_first_cached(&info->root);
> }
>
> fname = rb_entry(info->curr_node, struct fname, rb_hash);
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 9ebde0cd632e..0242c6801600 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -2116,7 +2116,7 @@ static inline bool ext4_is_quota_file(struct inode *inode)
> * readdir operations in hash tree order.
> */
> struct dir_private_info {
> - struct rb_root root;
> + struct rb_root_cached root;
> struct rb_node *curr_node;
> struct fname *extra_fname;
> loff_t last_pos;
> @@ -2883,7 +2883,7 @@ int ext4_update_disksize_before_punch(struct inode *inode, loff_t offset,
>
> struct ext4_group_info {
> unsigned long bb_state;
> - struct rb_root bb_free_root;
> + struct rb_root_cached bb_free_root;
> ext4_grpblk_t bb_first_free; /* first free block */
> ext4_grpblk_t bb_free; /* total free blocks */
> ext4_grpblk_t bb_fragments; /* nr of freespace fragments */
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 581e357e8406..df36f9123a99 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -2462,7 +2462,7 @@ int ext4_mb_add_groupinfo(struct super_block *sb, ext4_group_t group,
>
> INIT_LIST_HEAD(&meta_group_info[i]->bb_prealloc_list);
> init_rwsem(&meta_group_info[i]->alloc_sem);
> - meta_group_info[i]->bb_free_root = RB_ROOT;
> + meta_group_info[i]->bb_free_root = RB_ROOT_CACHED;
> meta_group_info[i]->bb_largest_free_order = -1; /* uninit */
>
> #ifdef DOUBLE_CHECK
> @@ -2824,7 +2824,7 @@ static void ext4_free_data_in_buddy(struct super_block *sb,
> count2++;
> ext4_lock_group(sb, entry->efd_group);
> /* Take it out of per group rb tree */
> - rb_erase(&entry->efd_node, &(db->bb_free_root));
> + rb_erase_cached(&entry->efd_node, &(db->bb_free_root));
> mb_free_blocks(NULL, &e4b, entry->efd_start_cluster, entry->efd_count);
>
> /*
> @@ -2836,7 +2836,7 @@ static void ext4_free_data_in_buddy(struct super_block *sb,
> if (!test_opt(sb, DISCARD))
> EXT4_MB_GRP_CLEAR_TRIMMED(db);
>
> - if (!db->bb_free_root.rb_node) {
> + if (!db->bb_free_root.rb_root.rb_node) {
> /* No more items in the per group rb tree
> * balance refcounts from ext4_mb_free_metadata()
> */
> @@ -3519,7 +3519,7 @@ static void ext4_mb_generate_from_freelist(struct super_block *sb, void *bitmap,
> struct ext4_free_data *entry;
>
> grp = ext4_get_group_info(sb, group);
> - n = rb_first(&(grp->bb_free_root));
> + n = rb_first_cached(&(grp->bb_free_root));
>
> while (n) {
> entry = rb_entry(n, struct ext4_free_data, efd_node);
> @@ -4624,7 +4624,7 @@ ext4_fsblk_t ext4_mb_new_blocks(handle_t *handle,
> static void ext4_try_merge_freed_extent(struct ext4_sb_info *sbi,
> struct ext4_free_data *entry,
> struct ext4_free_data *new_entry,
> - struct rb_root *entry_rb_root)
> + struct rb_root_cached *entry_rb_root)
> {
> if ((entry->efd_tid != new_entry->efd_tid) ||
> (entry->efd_group != new_entry->efd_group))
> @@ -4641,7 +4641,7 @@ static void ext4_try_merge_freed_extent(struct ext4_sb_info *sbi,
> spin_lock(&sbi->s_md_lock);
> list_del(&entry->efd_list);
> spin_unlock(&sbi->s_md_lock);
> - rb_erase(&entry->efd_node, entry_rb_root);
> + rb_erase_cached(&entry->efd_node, entry_rb_root);
> kmem_cache_free(ext4_free_data_cachep, entry);
> }
>
> @@ -4656,8 +4656,9 @@ ext4_mb_free_metadata(handle_t *handle, struct ext4_buddy *e4b,
> struct ext4_group_info *db = e4b->bd_info;
> struct super_block *sb = e4b->bd_sb;
> struct ext4_sb_info *sbi = EXT4_SB(sb);
> - struct rb_node **n = &db->bb_free_root.rb_node, *node;
> + struct rb_node **n = &db->bb_free_root.rb_root.rb_node, *node;
> struct rb_node *parent = NULL, *new_node;
> + bool leftmost = true;
>
> BUG_ON(!ext4_handle_valid(handle));
> BUG_ON(e4b->bd_bitmap_page == NULL);
> @@ -4680,9 +4681,10 @@ ext4_mb_free_metadata(handle_t *handle, struct ext4_buddy *e4b,
> entry = rb_entry(parent, struct ext4_free_data, efd_node);
> if (cluster < entry->efd_start_cluster)
> n = &(*n)->rb_left;
> - else if (cluster >= (entry->efd_start_cluster + entry->efd_count))
> + else if (cluster >= (entry->efd_start_cluster + entry->efd_count)) {
> n = &(*n)->rb_right;
> - else {
> + leftmost = false;
> + } else {
> ext4_grp_locked_error(sb, group, 0,
> ext4_group_first_block_no(sb, group) +
> EXT4_C2B(sbi, cluster),
> @@ -4692,7 +4694,7 @@ ext4_mb_free_metadata(handle_t *handle, struct ext4_buddy *e4b,
> }
>
> rb_link_node(new_node, parent, n);
> - rb_insert_color(new_node, &db->bb_free_root);
> + rb_insert_color_cached(new_node, &db->bb_free_root, leftmost);
>
> /* Now try to see the extent can be merged to left and right */
> node = rb_prev(new_node);
> --
> 2.12.0
>
--
Jan Kara <jack@...e.com>
SUSE Labs, CR
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