linux-kernel - Re: [PATCH v2] btrfs: use kmalloc for lzo de/compress buffer

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Date:	Thu, 21 Feb 2013 14:41:53 +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,
	hyojun.im@....com, chan.jeong@....com, raphael.andy.lee@...il.com,
	David Sterba <dsterba@...e.cz>
Subject: Re: [PATCH v2] btrfs: use kmalloc for lzo de/compress buffer

On Mon, Feb 18, 2013 at 04:56:04PM +0900, Kyungsik Lee wrote:
> @@ -55,8 +55,9 @@ static struct list_head *lzo_alloc_workspace(void)
>  		return ERR_PTR(-ENOMEM);
>  
>  	workspace->mem = vmalloc(LZO1X_MEM_COMPRESS);
> -	workspace->buf = vmalloc(PAGE_CACHE_SIZE);
> -	workspace->cbuf = vmalloc(lzo1x_worst_compress(PAGE_CACHE_SIZE));
> +	workspace->buf = kmalloc(PAGE_CACHE_SIZE, GFP_NOFS);
> +	workspace->cbuf = kmalloc(lzo1x_worst_compress(PAGE_CACHE_SIZE),

This is still larger than usual page size and allocator may issue a
warning, so if we want to use kmalloc (it's ~4.4k in size and likely to
be available, but not always due to possible page fragmentation), the
__GFP_NOWARN should be supplied and if the allocation fails fall back to
vmalloc.

david
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