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btrfs: defrag: bring back the old file extent search behavior
commit d5633b0 upstream. For defrag, we don't really want to use btrfs_get_extent() to iterate all extent maps of an inode. The reasons are: - btrfs_get_extent() can merge extent maps And the result em has the higher generation of the two, causing defrag to mark unnecessary part of such merged large extent map. This in fact can result extra IO for autodefrag in v5.16+ kernels. However this patch is not going to completely solve the problem, as one can still using read() to trigger extent map reading, and got them merged. The completely solution for the extent map merging generation problem will come as an standalone fix. - btrfs_get_extent() caches the extent map result Normally it's fine, but for defrag the target range may not get another read/write for a long long time. Such cache would only increase the memory usage. - btrfs_get_extent() doesn't skip older extent map Unlike the old find_new_extent() which uses btrfs_search_forward() to skip the older subtree, thus it will pick up unnecessary extent maps. This patch will fix the regression by introducing defrag_get_extent() to replace the btrfs_get_extent() call. This helper will: - Not cache the file extent we found It will search the file extent and manually convert it to em. - Use btrfs_search_forward() to skip entire ranges which is modified in the past This should reduce the IO for autodefrag. Reported-by: Filipe Manana <fdmanana@suse.com> Fixes: 7b50803 ("btrfs: defrag: use defrag_one_cluster() to implement btrfs_defrag_file()") Reviewed-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: Qu Wenruo <wqu@suse.com> Signed-off-by: David Sterba <dsterba@suse.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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