linux-kernel - RE: zsmalloc defrag (Was: [PATCH] mm: remove compressed copy from zram in-memory)

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Date:	Thu, 11 Apr 2013 10:53:10 -0700 (PDT)
From:	Dan Magenheimer <dan.magenheimer@...cle.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Hugh Dickins <hughd@...gle.com>,
	Seth Jennings <sjenning@...ux.vnet.ibm.com>,
	Nitin Gupta <ngupta@...are.org>,
	Konrad Rzeszutek Wilk <konrad@...nok.org>,
	Shaohua Li <shli@...nel.org>, Bob Liu <bob.liu@...cle.com>,
	Shuah Khan <shuah@...ehiking.org>
Subject: RE: zsmalloc defrag (Was: [PATCH] mm: remove compressed copy from
 zram in-memory)

> From: Minchan Kim [mailto:minchan@...nel.org]
> Subject: Re: zsmalloc defrag (Was: [PATCH] mm: remove compressed copy from zram in-memory)
> 
> On Tue, Apr 09, 2013 at 01:37:47PM -0700, Dan Magenheimer wrote:
> > > From: Minchan Kim [mailto:minchan@...nel.org]
> > > Subject: Re: zsmalloc defrag (Was: [PATCH] mm: remove compressed copy from zram in-memory)
> > >
> > > On Tue, Apr 09, 2013 at 10:27:19AM +0900, Minchan Kim wrote:
> > > > Hi Dan,
> > > >
> > > > On Mon, Apr 08, 2013 at 09:32:38AM -0700, Dan Magenheimer wrote:
> > > > > > From: Minchan Kim [mailto:minchan@...nel.org]
> > > > > > Sent: Monday, April 08, 2013 12:01 AM
> > > > > > Subject: [PATCH] mm: remove compressed copy from zram in-memory
> > > > >
> > > > > (patch removed)
> > > > >
> > > > > > Fragment ratio is almost same but memory consumption and compile time
> > > > > > is better. I am working to add defragment function of zsmalloc.
> > > > >
> > > > > Hi Minchan --
> > > > >
> > > > > I would be very interested in your design thoughts on
> > > > > how you plan to add defragmentation for zsmalloc.  In
> > > >
> > > > What I can say now about is only just a word "Compaction".
> > > > As you know, zsmalloc has a transparent handle so we can do whatever
> > > > under user. Of course, there is a tradeoff between performance
> > > > and memory efficiency. I'm biased to latter for embedded usecase.
> > > >
> > > > And I might post it because as you know well, zsmalloc
> > >
> > > Incomplete sentense,
> > >
> > > I might not post it until promoting zsmalloc because as you know well,
> > > zsmalloc/zram's all new stuffs are blocked into staging tree.
> > > Even if we could add it into staging, as you know well, staging is where
> > > every mm guys ignore so we end up needing another round to promote it. sigh.
> > >
> > > I hope it gets better after LSF/MM.
> >
> > If zsmalloc is moving in the direction of supporting only zram,
> > why should it be promoted into mm, or even lib?  Why not promote
> > zram into drivers and put zsmalloc.c in the same directory?
> 
> I don't want to make zsmalloc zram specific and will do best effort
> to generalize it to all z* familiy.

I'm glad to hear that.  You may not know/remember that the split between
"old zcache" and "new zcache" (and the fork to zswap) was started
because some people refused to accept changes to zsmalloc to
support a broader set of requirements.

> If it is hard to reach out
> agreement, yes, forking could be a easy solution like other embedded
> product company but I don't want it.

I don't want it either, so I think it is wise for us all to understand
each others' objectives to see if we can avoid a fork.  Or if the
objectives are too different, then we have data to explain to other kernel
developers why a fork is necessary.

Thanks!
Dan
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