linux-kernel - Re: [PATCH 2/2] staging: zcache: optional support for zsmalloc as alternate allocator

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Date:	Fri, 25 Jan 2013 11:26:17 -0800
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Dan Magenheimer <dan.magenheimer@...cle.com>
Cc:	devel@...uxdriverproject.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, ngupta@...are.org, konrad.wilk@...cle.com,
	sjenning@...ux.vnet.ibm.com, minchan@...nel.org
Subject: Re: [PATCH 2/2] staging: zcache: optional support for zsmalloc as
 alternate allocator

On Wed, Jan 23, 2013 at 01:46:31PM -0800, Dan Magenheimer wrote:
> "New" zcache uses zbud for all sub-page allocation which is more flexible but
> results in lower density.  "Old" zcache supported zsmalloc for frontswap
> pages.  Add zsmalloc to "new" zcache as a compile-time and run-time option
> for backwards compatibility in case any users wants to use zcache with
> highest possible density.
> 
> Note that most of the zsmalloc stats in old zcache are not included here
> because old zcache used sysfs and new zcache has converted to debugfs.
> These stats may be added later.
> 
> Note also that ramster is incompatible with zsmalloc as the two use
> the least significant bits in a pampd differently.
> 
> Signed-off-by: Dan Magenheimer <dan.magenheimer@...cle.com>
> ---
>  drivers/staging/zcache/Kconfig       |   11 ++
>  drivers/staging/zcache/zcache-main.c |  210 ++++++++++++++++++++++++++++++++--
>  drivers/staging/zcache/zcache.h      |    3 +
>  3 files changed, 215 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/staging/zcache/Kconfig b/drivers/staging/zcache/Kconfig
> index c1dbd04..116f8d5 100644
> --- a/drivers/staging/zcache/Kconfig
> +++ b/drivers/staging/zcache/Kconfig
> @@ -10,6 +10,17 @@ config ZCACHE
>  	  memory to store clean page cache pages and swap in RAM,
>  	  providing a noticeable reduction in disk I/O.
>  
> +config ZCACHE_ZSMALLOC
> +	bool "Allow use of zsmalloc allocator for compression of swap pages"
> +	depends on ZSMALLOC=y && !RAMSTER
> +	default n
> +	help
> +	  Zsmalloc is a much more efficient allocator for compresssed
> +	  pages but currently has some design deficiencies in that it
> +	  does not support reclaim nor compaction.  Select this if
> +	  you are certain your workload will fit or has mostly short
> +	  running processes.  Zsmalloc is incompatible with RAMster.

How can anyone be "certain"?


> --- a/drivers/staging/zcache/zcache-main.c
> +++ b/drivers/staging/zcache/zcache-main.c
> @@ -26,6 +26,12 @@
>  #include <linux/cleancache.h>
>  #include <linux/frontswap.h>
>  #include "tmem.h"
> +#ifdef CONFIG_ZCACHE_ZSMALLOC
> +#include "../zsmalloc/zsmalloc.h"

Don't #ifdef .h files in .c files.

> +static int zsmalloc_enabled;
> +#else
> +#define zsmalloc_enabled 0
> +#endif

That should have been your only ifdef in this .c file, all of the ones
you have after this should not be needed, so I can't take this patch,
sorry.

thanks,

greg k-h
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