linux-kernel - Re: [PATCHv2 4/9] staging: zsmalloc: make CLASS_DELTA relative to PAGE

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Message-ID: <CAPkvG_c48ZfwBRKCXSZrnVo=GgoLpqsRrF=8DEAwfFFVhb=1ZA@mail.gmail.com>
Date:	Thu, 24 Jan 2013 16:17:55 -0800
From:	Nitin Gupta <ngupta@...are.org>
To:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan@...nel.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	Robert Jennings <rcj@...ux.vnet.ibm.com>,
	Jenifer Hopper <jhopper@...ibm.com>,
	Mel Gorman <mgorman@...e.de>,
	Johannes Weiner <jweiner@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Larry Woodman <lwoodman@...hat.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, devel@...verdev.osuosl.org
Subject: Re: [PATCHv2 4/9] staging: zsmalloc: make CLASS_DELTA relative to PAGE_SIZE

On Mon, Jan 7, 2013 at 12:24 PM, Seth Jennings
<sjenning@...ux.vnet.ibm.com> wrote:
> Right now ZS_SIZE_CLASS_DELTA is hardcoded to be 16.  This
> creates 254 classes for systems with 4k pages. However, on
> PPC64 with 64k pages, it creates 4095 classes which is far
> too many.
>
> This patch makes ZS_SIZE_CLASS_DELTA relative to PAGE_SIZE
> so that regardless of the page size, there will be the same
> number of classes.
>
> Signed-off-by: Seth Jennings <sjenning@...ux.vnet.ibm.com>
> ---
>  drivers/staging/zsmalloc/zsmalloc-main.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/staging/zsmalloc/zsmalloc-main.c b/drivers/staging/zsmalloc/zsmalloc-main.c
> index 825e124..3543047 100644
> --- a/drivers/staging/zsmalloc/zsmalloc-main.c
> +++ b/drivers/staging/zsmalloc/zsmalloc-main.c
> @@ -141,7 +141,7 @@
>   *  ZS_MIN_ALLOC_SIZE and ZS_SIZE_CLASS_DELTA must be multiple of ZS_ALIGN
>   *  (reason above)
>   */
> -#define ZS_SIZE_CLASS_DELTA    16
> +#define ZS_SIZE_CLASS_DELTA    (PAGE_SIZE >> 8)
>  #define ZS_SIZE_CLASSES                ((ZS_MAX_ALLOC_SIZE - ZS_MIN_ALLOC_SIZE) / \
>                                         ZS_SIZE_CLASS_DELTA + 1)
>

Actually, there is no point creating size classes beyond [M/(M+1)] * PAGE_SIZE
where M is the maximum number of system pages in a zspage. All size classes
beyond this size can be collapsed with PAGE_SIZE size class.  This can
significantly reduce number of size classes created but I think changes needed
to do this would be more involved, so perhaps, should be done in another
patch.


Can you please resend part of this series  (patch 1  to patch 4) which deals
just with zsmalloc separately?  I haven't yet looked into zswap itself so would
help with zsmalloc bits are separated out.

Acked-by: Nitin Gupta <ngupta@...are.org>
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