On Tue, Mar 13, 2018 at 3:22 AM, Nikolay Borisov <nborisov@xxxxxxxx> wrote: > 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@xxxxxxxx> > --- > fs/btrfs/extent-tree.c | 45 +++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 45 insertions(+) > > diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c > index bb1861033071..60ece25101ee 100644 > --- a/fs/btrfs/extent-tree.c > +++ b/fs/btrfs/extent-tree.c > @@ -7961,6 +7961,51 @@ 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 contains this extent > + * > + * @ram_bytes - The amount of space in ram that @num_bytes take. This > + * is used for accounting purposes. This value differs > + * than @num_bytes only in the case of compressed extents. > + * > + * @num_bytes - Number of bytes to allocates on-disk. > + * > + * @min_alloc_size - Indicates the minimum amount of memory that the Could you please pick another word instead of "memory", like hole or extent or space? Others look good to me. Reviewed-by: Liu Bo <bo.liu@xxxxxxxxxxxxxxxxx> thanks, liubo > + * 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, > -- > 2.7.4 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
