Re: [patch 00/20] VM pageout scalability improvements

[Matt Mackall]

On Sun, 2007-12-23 at 20:11 -0500, Rik van Riel wrote:
> On Mon, 24 Dec 2007 04:29:36 +0530
> Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx> wrote:
> > Rik van Riel wrote:
> 
> > > In the real world, users with large JVMs on their servers, which
> > > sometimes go a little into swap, can trigger this system.  All of
> > > the CPUs end up scanning the active list, and all pages have the
> > > referenced bit set.  Even if the system eventually recovers, it
> > > might as well have been dead.
> > > 
> > > Going into swap a little should only take a little bit of time.
> > 
> > Very fascinating, so we need to scale better with larger memory.
> > I suspect part of the answer will lie with using large/huge pages.
> 
> Linus vetoed going to a larger soft page size, with good reason.
> 
> Just look at how much the 64kB page size on PPC64 sucks for most
> workloads - it works for PPC64 because people buy PPC64 monster
> systems for the kinds of monster workloads that work well with a
> large page size, but it definately isn't general purpose.

Indeed, machines already exist with >> 1TB of RAM, so even going to 1MB
pages leaves these machines in trouble. Going to big pages a few years
ago would have pushed the problem back a few years, but now we need real
fixes.

-- 
Mathematics is the supreme nostalgia of our time.

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