[PATCH v2] pstore: Adjust buffer size for compression for smaller registered buffers

[Seiji Aguchi]

efivars works fine with this v2 patch.

Tested-by: Seiji Aguchi <seiji.aguchi at hds.com>

> -----Original Message-----
> From: Aruna Balakrishnaiah [mailto:aruna at linux.vnet.ibm.com]
> Sent: Thursday, September 12, 2013 2:51 AM
> To: linuxppc-dev at ozlabs.org; tony.luck at intel.com; Seiji Aguchi; linux-kernel at vger.kernel.org; keescook at chromium.org
> Cc: jkenisto at linux.vnet.ibm.com; mahesh at linux.vnet.ibm.com; cbouatmailru at gmail.com; ananth at in.ibm.com; ccross at android.com
> Subject: [PATCH v2] pstore: Adjust buffer size for compression for smaller registered buffers
> 
> When backends (ex: efivars) have smaller registered buffers, the big_oops_buf
> is quite too big for them as number of repeated occurences in the text captured
> will be less. Patch takes care of adjusting the buffer size based on the
> registered buffer size. cmpr values has been arrived after doing experiments with
> plain text for buffers of size 1k - 4k (Smaller the buffer size repeated occurence
> will be less) and with sample crash log for buffers ranging from 4k - 10k.
> 
> Reported-by: Seiji Aguchi <seiji.aguchi at hds.com>
> Signed-off-by: Aruna Balakrishnaiah <aruna at linux.vnet.ibm.com>
> ---
> Changes from v1:
> 	Retain the cmpr = 45 for buffers ranging of size 4k - 10k. 45 seems to work.
> I added an additional headroom of 3%. Revert it back to 45.
> 
>  fs/pstore/platform.c |   23 ++++++++++++++++++++++-
>  1 file changed, 22 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
> index 4ffb7ab..57b4219 100644
> --- a/fs/pstore/platform.c
> +++ b/fs/pstore/platform.c
> @@ -195,8 +195,29 @@ error:
>  static void allocate_buf_for_compression(void)
>  {
>  	size_t size;
> +	size_t cmpr;
> +
> +	switch (psinfo->bufsize) {
> +	/* buffer range for efivars */
> +	case 1000 ... 2000:
> +		cmpr = 56;
> +		break;
> +	case 2001 ... 3000:
> +		cmpr = 54;
> +		break;
> +	case 3001 ... 3999:
> +		cmpr = 52;
> +		break;
> +	/* buffer range for nvram, erst */
> +	case 4000 ... 10000:
> +		cmpr = 45;
> +		break;
> +	default:
> +		cmpr = 60;
> +		break;
> +	}
> 
> -	big_oops_buf_sz = (psinfo->bufsize * 100) / 45;
> +	big_oops_buf_sz = (psinfo->bufsize * 100) / cmpr;
>  	big_oops_buf = kmalloc(big_oops_buf_sz, GFP_KERNEL);
>  	if (big_oops_buf) {
>  		size = max(zlib_deflate_workspacesize(WINDOW_BITS, MEM_LEVEL),