Re: [PATCH 0/3] Squashfs: Directly decompress into the page cache for file data

[Minchan Kim <minchan@kernel.org>]

Hello Phillip,

I looked at the patchset roughly and I feel it's really awesome
so I have to rebase decompressor_multi.c on it. 
But before that, could you review it?
I think you may have some stuff to hate like naming and even more.

Thanks.

On Fri, Oct 11, 2013 at 07:19:37AM +0100, Phillip Lougher wrote:
> This patch-set introduces an implementation of
> squashfs_readpage() that directly decompresses into the
> page cache.
> 
> It first generalises the decompressors by adding a page handler
> abstraction.  This adds helpers to allow the decompressors
> to access and process the output buffers in an implementation
> independant manner.
> 
> It then adds a read_page() implementation for file data that
> uses the 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-threaded 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
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-- 
Kind regards,
Minchan Kim