Re: [rfc][patch] unlock_page speedup

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 19 Dec 2008 08:53:28 +0100 Nick Piggin <npiggin@suse.de> wrote:

> On Thu, Dec 18, 2008 at 11:35:49PM -0800, Andrew Morton wrote:
> > On Fri, 19 Dec 2008 08:29:09 +0100 Nick Piggin <npiggin@suse.de> wrote:
> > 
> > > Introduce a new page flag, PG_waiters
> > 
> > Leaving how many?
> 
> Don't know...

Need to know!  page.flags is prime real estate and we should decide
whether gaining 2% in a particular microbenchmark is our best use of it

> I thought the page-flags.h obfuscation project was
> supposed to make that clearer to work out. There are what, 21 flags
> used now. If everything is coded properly, then the memory model
> should automatically kick its metadata out of page flags if it gets
> too big.

That would be nice :)

> But most likely it will just blow up.

If we use them all _now_, as I proposed, we'll find out about that.

> Probably we want
> at least a few flags for memory model on 32-bit for smaller systems
> (big NUMA 32-bit systems probably don't matter much anymore).
> 
> 
> >  fs-cache wants to take two more.
> 
> fs-cache is getting merged?

See thread titled "Pull request for FS-Cache, including NFS patches"

> Wow, I've wanted to review that.

That would be good.