linux-kernel - RE: zsmalloc limitations and related topics

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <006139fe-542e-46f0-8b6c-b05efeb232d6@default>
Date:	Thu, 14 Mar 2013 11:54:35 -0700 (PDT)
From:	Dan Magenheimer <dan.magenheimer@...cle.com>
To:	Robert Jennings <rcj@...ux.vnet.ibm.com>,
	Bob Liu <bob.liu@...cle.com>
Cc:	Seth Jennings <sjenning@...ux.vnet.ibm.com>, minchan@...nel.org,
	Nitin Gupta <nitingupta910@...il.com>,
	Konrad Wilk <konrad.wilk@...cle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Bob Liu <lliubbo@...il.com>,
	Luigi Semenzato <semenzato@...gle.com>,
	Mel Gorman <mgorman@...e.de>
Subject: RE: zsmalloc limitations and related topics

> From: Robert Jennings [mailto:rcj@...ux.vnet.ibm.com]
> Sent: Thursday, March 14, 2013 7:21 AM
> To: Bob
> Cc: Seth Jennings; Dan Magenheimer; minchan@...nel.org; Nitin Gupta; Konrad Wilk; linux-mm@...ck.org;
> linux-kernel@...r.kernel.org; Bob Liu; Luigi Semenzato; Mel Gorman
> Subject: Re: zsmalloc limitations and related topics
> 
> * Bob (bob.liu@...cle.com) wrote:
> > On 03/14/2013 06:59 AM, Seth Jennings wrote:
> > >On 03/13/2013 03:02 PM, Dan Magenheimer wrote:
> > >>>From: Robert Jennings [mailto:rcj@...ux.vnet.ibm.com]
> > >>>Subject: Re: zsmalloc limitations and related topics
> > >>
> <snip>
> > >>Yes.  And add pageframe-reclaim to this list of things that
> > >>zsmalloc should do but currently cannot do.
> > >
> > >The real question is why is pageframe-reclaim a requirement?  What
> > >operation needs this feature?
> > >
> > >AFAICT, the pageframe-reclaim requirements is derived from the
> > >assumption that some external control path should be able to tell
> > >zswap/zcache to evacuate a page, like the shrinker interface.  But this
> > >introduces a new and complex problem in designing a policy that doesn't
> > >shrink the zpage pool so aggressively that it is useless.
> > >
> > >Unless there is another reason for this functionality I'm missing.
> > >
> >
> > Perhaps it's needed if the user want to enable/disable the memory
> > compression feature dynamically.
> > Eg, use it as a module instead of recompile the kernel or even
> > reboot the system.

It's worth thinking about: Under what circumstances would a user want
to turn off compression?  While unloading a compression module should
certainly be allowed if it makes a user comfortable, in my opinion,
if a user wants to do that, we have done our job poorly (or there
is a bug).

> To unload zswap all that is needed is to perform writeback on the pages
> held in the cache, this can be done by extending the existing writeback
> code.

Actually, frontswap supports this directly.  See frontswap_shrink.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/