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 <jbacik@fb.com> Signed-off-by: Chris Mason <clm@fb.com>
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@ -9687,6 +9687,7 @@ static int __btrfs_prealloc_file_range(struct inode *inode, int mode,
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u64 cur_offset = start;
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u64 i_size;
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u64 cur_bytes;
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u64 last_alloc = (u64)-1;
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int ret = 0;
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bool own_trans = true;
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@ -9703,6 +9704,13 @@ static int __btrfs_prealloc_file_range(struct inode *inode, int mode,
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cur_bytes = min(num_bytes, 256ULL * 1024 * 1024);
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cur_bytes = max(cur_bytes, min_size);
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/*
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* If we are severely fragmented we could end up with really
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* small allocations, so if the allocator is returning small
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* chunks lets make its job easier by only searching for those
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* sized chunks.
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*/
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cur_bytes = min(cur_bytes, last_alloc);
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ret = btrfs_reserve_extent(root, cur_bytes, min_size, 0,
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*alloc_hint, &ins, 1, 0);
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if (ret) {
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@ -9711,6 +9719,7 @@ static int __btrfs_prealloc_file_range(struct inode *inode, int mode,
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break;
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}
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last_alloc = ins.offset;
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ret = insert_reserved_file_extent(trans, inode,
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cur_offset, ins.objectid,
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ins.offset, ins.offset,
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