ext4: track all extent status in extent status tree
By recording the phycisal block and status, extent status tree is able to track the status of every extents. When we call _map_blocks functions to lookup an extent or create a new written/unwritten/delayed extent, this extent will be inserted into extent status tree. We don't load all extents from disk in alloc_inode() because it costs too much memory, and if a file is opened and closed frequently it will takes too much time to load all extent information. So currently when we create/lookup an extent, this extent will be inserted into extent status tree. Hence, the extent status tree may not comprehensively contain all of the extents found in the file. Here a condition we need to take care is that an extent might contains unwritten and delayed status simultaneously because an extent is delayed allocated and could be allocated by fallocate. At this time we need to keep delayed status because later we need to update delayed reservation space using it. Signed-off-by: NZheng Liu <wenqing.lz@taobao.com> Signed-off-by: N"Theodore Ts'o" <tytso@mit.edu> Cc: Jan kara <jack@suse.cz>
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