linux-kernel - Re: [PATCH] mm: Revert pinned

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Date:	Thu, 20 Jun 2013 13:34:31 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	torvalds@...ux-foundation.org, roland@...nel.org,
	kosaki.motohiro@...il.com, penberg@...nel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-rdma@...r.kernel.org, Mike Marciniszyn <infinipath@...el.com>
Subject: Re: [PATCH] mm: Revert pinned_vm braindamage


* Thomas Gleixner <tglx@...utronix.de> wrote:

> On Thu, 13 Jun 2013, Andrew Morton wrote:
> > Let's try to get this wrapped up?
> > 
> > On Thu, 6 Jun 2013 14:43:51 +0200 Peter Zijlstra <peterz@...radead.org> wrote:
> > 
> > > 
> > > Patch bc3e53f682 ("mm: distinguish between mlocked and pinned pages")
> > > broke RLIMIT_MEMLOCK.
> > 
> > I rather like what bc3e53f682 did, actually.  RLIMIT_MEMLOCK limits the
> > amount of memory you can mlock().  Nice and simple.
> > 
> > This pinning thing which infiniband/perf are doing is conceptually
> > different and if we care at all, perhaps we should be looking at adding
> > RLIMIT_PINNED.
> 
> Actually PINNED is just a stronger version of MEMLOCK. PINNED and 
> MEMLOCK are both preventing the page from being paged out. PINNED adds 
> the constraint of preventing minor faults as well.
> 
> So I think the really important tuning knob is the limitation of pages 
> which cannot be paged out. And this is what RLIMIT_MEMLOCK is about.
> 
> Now if you want to add RLIMIT_PINNED as well, then it only limits the 
> number of pages which cannot create minor faults, but that does not 
> affect the limitation of total pages which cannot be paged out.

Agreed.

( Furthermore, the RLIMIT_MEMLOCK semantics change actively broke code so
  this is not academic and it would be nice to progress with it. )

Thanks,

	Ingo
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