Btrfs: fix prealloc under heavy fragmentation conditions (0b670dc4) · Commits · 戴 / test

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:

Josef Bacik <jbacik@fb.com> Signed-off-by:

Chris Mason <clm@fb.com>

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,

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