linux-kernel - Re: [PATCH 1/3] staging: zcache: xcfmalloc memory allocator for zcache

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Date:	Thu, 01 Sep 2011 10:43:27 -0500
From:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
To:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
CC:	gregkh@...e.de, devel@...verdev.osuosl.org,
	dan.magenheimer@...cle.com, ngupta@...are.org,
	cascardo@...oscopio.com, rdunlap@...otime.net,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] staging: zcache: xcfmalloc memory allocator for zcache

On 08/31/2011 09:40 AM, Seth Jennings wrote:

> +static struct xcf_blkdesc *xcf_find_remove_block(struct xcf_pool *pool,
> +	int size, int blocknum)
> +{
> +	int flindex, i;
> +	struct xcf_blkdesc *desc = NULL;
> +
> +	flindex = xcf_size_to_flindex(size + sizeof(struct xcf_blkhdr));
> +
> +	/* look for best fit */
> +	if (pool->freelists[flindex])
> +		goto remove;
> +
> +	/* if this is the last block allowed in the allocation, we shouldn't
> +	 * consider smaller blocks.  it's all or nothing now */
> +	if (blocknum == XCF_MAX_BLOCKS_PER_ALLOC) {

In gathering my performance numbers for Dan, I discovered I introduced
a regression by making a late change in my development.

This line should be:
	if (blocknum != XCF_MAX_BLOCKS_PER_ALLOC) {

This regression actually causes xcfmalloc to have the same fragmentation
issue as xvmalloc.

> +		/* look for largest smaller block */
> +		for (i = flindex; i > 0; i--) {
> +			if (pool->freelists[i]) {
> +				flindex = i;
> +				goto remove;
> +			}
> +		}
> +	}

--
Seth
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