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    Btrfs: Cache free inode numbers in memory · 581bb050
    Li Zefan 提交于
    Currently btrfs stores the highest objectid of the fs tree, and it always
    returns (highest+1) inode number when we create a file, so inode numbers
    won't be reclaimed when we delete files, so we'll run out of inode numbers
    as we keep create/delete files in 32bits machines.
    
    This fixes it, and it works similarly to how we cache free space in block
    cgroups.
    
    We start a kernel thread to read the file tree. By scanning inode items,
    we know which chunks of inode numbers are free, and we cache them in
    an rb-tree.
    
    Because we are searching the commit root, we have to carefully handle the
    cross-transaction case.
    
    The rb-tree is a hybrid extent+bitmap tree, so if we have too many small
    chunks of inode numbers, we'll use bitmaps. Initially we allow 16K ram
    of extents, and a bitmap will be used if we exceed this threshold. The
    extents threshold is adjusted in runtime.
    Signed-off-by: NLi Zefan <lizf@cn.fujitsu.com>
    581bb050
transaction.c 37.3 KB