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Commit 0b670dc4 authored by Josef Bacik's avatar Josef Bacik Committed by Chris Mason
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Btrfs: fix prealloc under heavy fragmentation conditions 



If we are heavily fragmented we will continually try to prealloc the largest
extent size we can every time we call btrfs_reserve_extent.  This can be very
expensive when we are heavily fragmented, burning lots of CPU cycles and loops
through the allocator.  So instead notice when we get a smaller chunk from the
allocator than what we specified and use this as the new maximum size we try to
allocate.  Thanks,

Signed-off-by: default avatarJosef Bacik <jbacik@fb.com>
Signed-off-by: default avatarChris Mason <clm@fb.com>
parent d0bd4560

fs/btrfs/inode.c

+9 −0
Original line number Diff line number Diff line
@@ -9687,6 +9687,7 @@ static int __btrfs_prealloc_file_range(struct inode *inode, int mode, 
	u64 cur_offset = start;

	u64 i_size;

	u64 cur_bytes;

	u64 last_alloc = (u64)-1;

	int ret = 0;

	bool own_trans = true;
@@ -9703,6 +9704,13 @@ static int __btrfs_prealloc_file_range(struct inode *inode, int mode, 


		cur_bytes = min(num_bytes, 256ULL * 1024 * 1024);

		cur_bytes = max(cur_bytes, min_size);

		/*

		 * If we are severely fragmented we could end up with really

		 * small allocations, so if the allocator is returning small

		 * chunks lets make its job easier by only searching for those

		 * sized chunks.

		 */

		cur_bytes = min(cur_bytes, last_alloc);

		ret = btrfs_reserve_extent(root, cur_bytes, min_size, 0,

					   *alloc_hint, &ins, 1, 0);

		if (ret) {
@@ -9711,6 +9719,7 @@ static int __btrfs_prealloc_file_range(struct inode *inode, int mode, 
			break;

		}



		last_alloc = ins.offset;

		ret = insert_reserved_file_extent(trans, inode,

						  cur_offset, ins.objectid,

						  ins.offset, ins.offset,