linux-kernel - Re: [PATCH] btrfs compression: merge inflate and deflate z

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Date:	Tue, 1 Jul 2014 16:44:15 +0200
From:	David Sterba <dsterba@...e.cz>
To:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:	Chris Mason <clm@...com>, Josef Bacik <jbacik@...com>,
	linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] btrfs compression: merge inflate and deflate z_streams

On Tue, Jul 01, 2014 at 12:32:10AM +0900, Sergey Senozhatsky wrote:
> `struct workspace' used for zlib compression contains two zlib
> z_stream-s: `def_strm' used in zlib_compress_pages(), and `inf_strm'
> used in zlib_decompress/zlib_decompress_biovec(). None of these
> functions use `inf_strm' and `def_strm' simultaniously, meaning that
> for every compress/decompress operation we need only one z_stream
> (out of two available).
> 
> `inf_strm' and `def_strm' are different in size of ->workspace. For
> inflate stream we vmalloc() zlib_inflate_workspacesize() bytes, for
> deflate stream - zlib_deflate_workspacesize() bytes. On my system zlib
> returns the following workspace sizes, correspondingly: 42312 and 268104
> (+ guard pages).
> 
> Keep only one `z_stream' in `struct workspace' and use it for both
> compression and decompression. Hence, instead of vmalloc() of two
> z_stream->worskpace-s, allocate only one of size:
> 	max(zlib_deflate_workspacesize(), zlib_inflate_workspacesize())
> 
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>

Reviewed-by: David Sterba <dsterba@...e.cz>
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