linux-kernel - Re: [PATCH 0/5] mm: i_mmap

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Date:	Mon, 02 Jun 2014 13:31:01 -0700
From:	Davidlohr Bueso <davidlohr@...com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	mingo@...nel.org, peterz@...radead.org, riel@...hat.com,
	mgorman@...e.de, aswin@...com, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/5] mm: i_mmap_mutex to rwsem

On Mon, 2014-06-02 at 13:08 -0700, Andrew Morton wrote:
> On Thu, 29 May 2014 19:20:15 -0700 Davidlohr Bueso <davidlohr@...com> wrote:
> 
> > On Thu, 2014-05-22 at 20:33 -0700, Davidlohr Bueso wrote:
> > > This patchset extends the work started by Ingo Molnar in late 2012,
> > > optimizing the anon-vma mutex lock, converting it from a exclusive mutex
> > > to a rwsem, and sharing the lock for read-only paths when walking the
> > > the vma-interval tree. More specifically commits 5a505085 and 4fc3f1d6.
> > > 
> > > The i_mmap_mutex has similar responsibilities with the anon-vma, protecting
> > > file backed pages. Therefore we can use similar locking techniques: covert
> > > the mutex to a rwsem and share the lock when possible.
> > > 
> > > With the new optimistic spinning property we have in rwsems, we no longer
> > > take a hit in performance when using this lock, and we can therefore
> > > safely do the conversion. Tests show no throughput regressions in aim7 or
> > > pgbench runs, and we can see gains from sharing the lock, in disk workloads
> > > ~+15% for over 1000 users on a 8-socket Westmere system.
> > > 
> > > This patchset applies on linux-next-20140522.
> >
> > ping? Andrew any chance of getting this in -next?
> 
> (top-posting repaired)
> 
> It was a bit late for 3.16 back on May 26, when you said "I will dig
> deeper (probably for 3.17 now)".  So, please take another look at the
> patch factoring and let's get this underway for -rc1.

Ok, so I meant that I'd dig deeper for the additional sharing
opportunities (which I've found a few as Hugh correctly suggested). So
those eventual patches could come later. 

But I see no reason for *this* patchset to be delayed, as even if it
gets to be 3.17 material, I'd still very much want to have the same
patch factoring I have now. I think its the correct way to handle lock
transitioning for both correctness and bisectability.

Thanks,
Davidlohr


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