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btrfs: reduce size of struct tree_mod_elem 

Several members are used for specific types of tree mod log operations so
they can be placed in a union in order to reduce the structure's size.

This reduces the structure size from 112 bytes to 88 bytes on x86_64,
so we can now use the kmalloc-96 slab instead of the kmalloc-128 slab.

Reviewed-by: Boris Burkov <boris@bur.io>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
pull/1309/head
Filipe Manana 2025-07-01 23:01:56 +01:00 committed by David Sterba
parent d30b236a3e
commit aee10fe4e4
1 changed files with 31 additions and 18 deletions
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49
fs/btrfs/tree-mod-log.c
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@ -27,18 +27,29 @@ struct tree_mod_elem {
/* This is used for BTRFS_MOD_LOG_KEY* and BTRFS_MOD_LOG_ROOT_REPLACE. */
u64 generation;
/* Those are used for op == BTRFS_MOD_LOG_KEY_{REPLACE,REMOVE}. */
struct btrfs_disk_key key;
u64 blockptr;
union {
/*
* This is used for the following op types:
*
* BTRFS_MOD_LOG_KEY_REMOVE_WHILE_FREEING
* BTRFS_MOD_LOG_KEY_REMOVE_WHILE_MOVING
* BTRFS_MOD_LOG_KEY_REMOVE
* BTRFS_MOD_LOG_KEY_REPLACE
*/
struct {
struct btrfs_disk_key key;
u64 blockptr;
} slot_change;
/* This is used for op == BTRFS_MOD_LOG_MOVE_KEYS. */
struct {
int dst_slot;
int nr_items;
} move;
/* This is used for op == BTRFS_MOD_LOG_MOVE_KEYS. */
struct {
int dst_slot;
int nr_items;
} move;
/* This is used for op == BTRFS_MOD_LOG_ROOT_REPLACE. */
struct tree_mod_root old_root;
/* This is used for op == BTRFS_MOD_LOG_ROOT_REPLACE. */
struct tree_mod_root old_root;
};
};
/*
@ -228,15 +239,17 @@ static struct tree_mod_elem *alloc_tree_mod_elem(const struct extent_buffer *eb,
{
struct tree_mod_elem *tm;
/* Can't be one of these types, due to union in struct tree_mod_elem. */
ASSERT(op != BTRFS_MOD_LOG_MOVE_KEYS);
ASSERT(op != BTRFS_MOD_LOG_ROOT_REPLACE);
tm = kzalloc(sizeof(*tm), GFP_NOFS);
if (!tm)
return NULL;
tm->logical = eb->start;
if (op != BTRFS_MOD_LOG_KEY_ADD) {
btrfs_node_key(eb, &tm->key, slot);
tm->blockptr = btrfs_node_blockptr(eb, slot);
}
btrfs_node_key(eb, &tm->slot_change.key, slot);
tm->slot_change.blockptr = btrfs_node_blockptr(eb, slot);
tm->op = op;
tm->slot = slot;
tm->generation = btrfs_node_ptr_generation(eb, slot);
@ -854,8 +867,8 @@ static void tree_mod_log_rewind(struct btrfs_fs_info *fs_info,
fallthrough;
case BTRFS_MOD_LOG_KEY_REMOVE_WHILE_MOVING:
case BTRFS_MOD_LOG_KEY_REMOVE:
btrfs_set_node_key(eb, &tm->key, tm->slot);
btrfs_set_node_blockptr(eb, tm->slot, tm->blockptr);
btrfs_set_node_key(eb, &tm->slot_change.key, tm->slot);
btrfs_set_node_blockptr(eb, tm->slot, tm->slot_change.blockptr);
btrfs_set_node_ptr_generation(eb, tm->slot,
tm->generation);
n++;
@ -864,8 +877,8 @@ static void tree_mod_log_rewind(struct btrfs_fs_info *fs_info,
break;
case BTRFS_MOD_LOG_KEY_REPLACE:
BUG_ON(tm->slot >= n);
btrfs_set_node_key(eb, &tm->key, tm->slot);
btrfs_set_node_blockptr(eb, tm->slot, tm->blockptr);
btrfs_set_node_key(eb, &tm->slot_change.key, tm->slot);
btrfs_set_node_blockptr(eb, tm->slot, tm->slot_change.blockptr);
btrfs_set_node_ptr_generation(eb, tm->slot,
tm->generation);
break;