linux-kernel - Re: [PATCH] btrfs: use kmalloc for lzo de/compress buffer

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Message-ID: <20130215131724.GP12339@twin.jikos.cz>
Date:	Fri, 15 Feb 2013 14:17:24 +0100
From:	David Sterba <dsterba@...e.cz>
To:	Kyungsik Lee <kyungsik.lee@....com>
Cc:	Chris Mason <chris.mason@...ionio.com>,
	linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	David Sterba <dsterba@...e.cz>, hyojun.im@....com,
	chan.jeong@....com, raphael.andy.lee@...il.com
Subject: Re: [PATCH] btrfs: use kmalloc for lzo de/compress buffer

On Fri, Feb 15, 2013 at 10:08:21PM +0900, Kyungsik Lee wrote:
> The size of de/compress buffer and LZO1X_MEM_COMPRESS is small enough.

Unfortunatelly it is not.

include/linux/lzo.h:

#define LZO1X_MEM_COMPRESS      (16384 * sizeof(unsigned char *))

128k with 8 byte pointers

> @@ -54,9 +53,10 @@ static struct list_head *lzo_alloc_workspace(void)
>  	if (!workspace)
>  		return ERR_PTR(-ENOMEM);
>  
> -	workspace->mem = vmalloc(LZO1X_MEM_COMPRESS);

vmalloc needed

> -	workspace->buf = vmalloc(PAGE_CACHE_SIZE);

kmalloc is ok here

> -	workspace->cbuf = vmalloc(lzo1x_worst_compress(PAGE_CACHE_SIZE));

#define lzo1x_worst_compress(x) ((x) + ((x) / 16) + 64 + 3)

4096+4096/16+64+3 = 4419

vmalloc needed as well

david
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