Re: [PATCHv6 00/22] Transparent huge page cache: phase 1, everythingbut mmap()

From: Mel Gorman
Date: Mon Sep 30 2013 - 06:10:55 EST

On Mon, Sep 30, 2013 at 11:02:49AM +0100, Mel Gorman wrote:
> On Tue, Sep 24, 2013 at 04:37:40PM -0700, Andrew Morton wrote:
> > On Mon, 23 Sep 2013 15:05:28 +0300 "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> wrote:
> >
> > > It brings thp support for ramfs, but without mmap() -- it will be posted
> > > separately.
> >
> > We were never going to do this :(
> >
> > Has anyone reviewed these patches much yet?
> >
> I am afraid I never looked too closely once I learned that the primary
> motivation for this was relieving iTLB pressure in a very specific
> case. AFAIK, this is not a problem in the vast majority of modern CPUs
> and I found it very hard to be motivated to review the series as a result.
> I suspected that in many cases that the cost of IO would continue to dominate
> performance instead of TLB pressure. I also found it unlikely that there
> was a workload that was tmpfs based that used enough memory to be hurt
> by TLB pressure. My feedback was that a much more compelling case for the
> series was needed but this discussion all happened on IRC unfortunately.

Oh, one last thing I forgot. While tmpfs-based workloads were not likely to
benefit I would expect that sysV shared memory workloads would potentially
benefit from this. hugetlbfs is still required for shared memory areas
but it is not a problem that is addressed by this series.

Mel Gorman
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