linux-kernel - RE: [PATCH part2 v6 0/3] staging: zcache: Support zero-filled pages more efficiently

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Date:	Sun, 7 Apr 2013 10:51:27 -0700 (PDT)
From:	Dan Magenheimer <dan.magenheimer@...cle.com>
To:	Wanpeng Li <liwanp@...ux.vnet.ibm.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Seth Jennings <sjenning@...ux.vnet.ibm.com>,
	Konrad Rzeszutek Wilk <konrad@...nok.org>,
	Minchan Kim <minchan@...nel.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Fengguang Wu <fengguang.wu@...el.com>,
	Bob Liu <bob.liu@...cle.com>, Ric Mason <ric.masonn@...il.com>
Subject: RE: [PATCH part2 v6 0/3] staging: zcache: Support zero-filled pages
 more efficiently

> From: Wanpeng Li [mailto:liwanp@...ux.vnet.ibm.com]
> Subject: Re: [PATCH part2 v6 0/3] staging: zcache: Support zero-filled pages more efficiently
> 
> Hi Dan,
> 
> Some issues against Ramster:
> 
> - Ramster who takes advantage of zcache also should support zero-filled
>   pages more efficiently, correct? It doesn't handle zero-filled pages well
>   currently.

When you first posted your patchset I took a quick look at ramster
and it looked like your patchset should work for ramster also.
However I didn't actually run ramster to try it so there may
be a bug.  If it doesn't work, I would very much appreciate a patch.

> - Ramster DebugFS counters are exported in /sys/kernel/mm/, but zcache/frontswap/cleancache
>   all are exported in /sys/kernel/debug/, should we unify them?

That would be great.

> - If ramster also should move DebugFS counters to a single file like
>   zcache do?

Sure!  I am concerned about Konrad's patches adding debug.c as they
add many global variables.  They are only required when ZCACHE_DEBUG
is enabled so they may be ok.  If not, adding ramster variables
to debug.c may make the problem worse.

> If you confirm these issues are make sense to fix, I will start coding. ;-)

That would be great.  Note that I have a how-to for ramster here:

https://oss.oracle.com/projects/tmem/dist/files/RAMster/HOWTO-120817 

If when you are testing you find that this how-to has mistakes,
please let me know.  Or feel free to add the (corrected) how-to file
as a patch in your patchset.

Thanks very much, Wanpeng, for your great contributions!

(Ric, since you have expressed interest in ramster, if you try it and
find corrections to the how-to file above, your input would be
very much appreciated also!)

Dan
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