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btrfs: avoid unnecessary memory allocation and copy at overwrite_item()

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There's no need to allocate memory and copy from both the destination and
source extent buffers to compare if the items are equal, we can instead
use memcmp_extent_buffer() which allows to do only one memory allocation
and copy instead of two.

So use memcmp_extent_buffer() instead of memcmp(), allowing us to avoid
one memory allocation, which can fail or be slow while under memory heavy
pressure, avoid the memory copying and reducing code.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Filipe Manana 2025-03-13 14:00:52 +00:00 • committed by David Sterba
parent 9db9c7dd5b
commit e48264e601
1 changed files with 2 additions and 10 deletions
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12
fs/btrfs/tree-log.c
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@ -422,7 +422,6 @@ static int overwrite_item(struct btrfs_trans_handle *trans,
if (ret == 0) {
char *src_copy;
char *dst_copy;
u32 dst_size = btrfs_item_size(path->nodes[0],
path->slots[0]);
if (dst_size != item_size)
@ -432,23 +431,16 @@ static int overwrite_item(struct btrfs_trans_handle *trans,
btrfs_release_path(path);
return 0;
}
dst_copy = kmalloc(item_size, GFP_NOFS);
src_copy = kmalloc(item_size, GFP_NOFS);
if (!dst_copy || !src_copy) {
if (!src_copy) {
btrfs_release_path(path);
kfree(dst_copy);
kfree(src_copy);
return -ENOMEM;
}
read_extent_buffer(eb, src_copy, src_ptr, item_size);
dst_ptr = btrfs_item_ptr_offset(path->nodes[0], path->slots[0]);
read_extent_buffer(path->nodes[0], dst_copy, dst_ptr,
item_size);
ret = memcmp(dst_copy, src_copy, item_size);
ret = memcmp_extent_buffer(path->nodes[0], src_copy, dst_ptr, item_size);
kfree(dst_copy);
kfree(src_copy);
/*
* they have the same contents, just return, this saves