• Phillip Lougher's avatar
    Squashfs: Directly decompress into the page cache for file data · 0d455c12
    Phillip Lougher authored
    This introduces an implementation of squashfs_readpage_block()
    that directly decompresses into the page cache.
    
    This uses the previously added page handler abstraction to push
    down the necessary kmap_atomic/kunmap_atomic operations on the
    page cache buffers into the decompressors.  This enables
    direct copying into the page cache without using the slow
    kmap/kunmap calls.
    
    The code detects when multiple threads are racing in
    squashfs_readpage() to decompress the same block, and avoids
    this regression by falling back to using an intermediate
    buffer.
    
    This patch enhances the performance of Squashfs significantly
    when multiple processes are accessing the filesystem simultaneously
    because it not only reduces memcopying, but it more importantly
    eliminates the lock contention on the intermediate buffer.
    
    Using single-thread decompression.
    
            dd if=file1 of=/dev/null bs=4096 &
            dd if=file2 of=/dev/null bs=4096 &
            dd if=file3 of=/dev/null bs=4096 &
            dd if=file4 of=/dev/null bs=4096
    
    Before:
    
    629145600 bytes (629 MB) copied, 45.8046 s, 13.7 MB/s
    
    After:
    
    629145600 bytes (629 MB) copied, 9.29414 s, 67.7 MB/s
    Signed-off-by: 's avatarPhillip Lougher <phillip@squashfs.org.uk>
    Reviewed-by: 's avatarMinchan Kim <minchan@kernel.org>
    0d455c12
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