From 0b670dc44c91bd1e5fac15b5ac4c98c8bd255ca2 Mon Sep 17 00:00:00 2001 From: Josef Bacik Date: Wed, 23 Sep 2015 17:11:16 -0400 Subject: [PATCH] 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: Josef Bacik Signed-off-by: Chris Mason --- fs/btrfs/inode.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index 5ce55f6eefce..a3e078365de5 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -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, -- 2.20.1