AuxXxilium/linux_dsm_epyc7002
1
0
Fork 0
mirror of https://github.com/AuxXxilium/linux_dsm_epyc7002.git synced 2025-01-21 17:41:34 +07:00
Code Issues Actions Packages Projects Releases Wiki Activity

btrfs: Document parameters of btrfs_reserve_extent

Browse Source 
This function is the entry to the extent allocator and as such has
quite a number of parameters. Some of those have subtle effects on the
allocation algorithm. Document the parameters.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Nikolay Borisov 2018-03-13 12:22:32 +02:00 committed by David Sterba
parent d87ff75863
commit 6f47c706d9
1 changed files with 45 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

45
fs/btrfs/extent-tree.c
View File

@ -7968,6 +7968,51 @@ static void dump_space_info(struct btrfs_fs_info *fs_info,
up_read(&info->groups_sem);
}
/*
* btrfs_reserve_extent - entry point to the extent allocator. Tries to find a
* hole that is at least as big as @num_bytes.
*
* @root - The root that will contain this extent
*
* @ram_bytes - The amount of space in ram that @num_bytes take. This
* is used for accounting purposes. This value differs
* from @num_bytes only in the case of compressed extents.
*
* @num_bytes - Number of bytes to allocate on-disk.
*
* @min_alloc_size - Indicates the minimum amount of space that the
* allocator should try to satisfy. In some cases
* @num_bytes may be larger than what is required and if
* the filesystem is fragmented then allocation fails.
* However, the presence of @min_alloc_size gives a
* chance to try and satisfy the smaller allocation.
*
* @empty_size - A hint that you plan on doing more COW. This is the
* size in bytes the allocator should try to find free
* next to the block it returns. This is just a hint and
* may be ignored by the allocator.
*
* @hint_byte - Hint to the allocator to start searching above the byte
* address passed. It might be ignored.
*
* @ins - This key is modified to record the found hole. It will
* have the following values:
* ins->objectid == start position
* ins->flags = BTRFS_EXTENT_ITEM_KEY
* ins->offset == the size of the hole.
*
* @is_data - Boolean flag indicating whether an extent is
* allocated for data (true) or metadata (false)
*
* @delalloc - Boolean flag indicating whether this allocation is for
* delalloc or not. If 'true' data_rwsem of block groups
* is going to be acquired.
*
*
* Returns 0 when an allocation succeeded or < 0 when an error occurred. In
* case -ENOSPC is returned then @ins->offset will contain the size of the
* largest available hole the allocator managed to find.
*/
int btrfs_reserve_extent(struct btrfs_root *root, u64 ram_bytes,
u64 num_bytes, u64 min_alloc_size,
u64 empty_size, u64 hint_byte,