Re: 3rd version of R/W mmap_sem patch available

[ebiederman@lnxi.com (Eric W. Biederman)]

Andrew Morton <andrewm@uow.edu.au> writes:

> Jeff Garzik wrote:
> > 
> > Andrew Morton wrote:
> > > General comment: an expensive part of a pagefault
> > > is zeroing the new page.  It'd be nice if we could
> > > drop the page_table_lock while doing the clear_user_page()
> > > and, if possible, copy_user_page() functions.  Very nice.
> > 
> > People have talked before about creating zero pages in the background,
> > or creating them as a side effect of another operation (don't recall
> > details), so yeah this is definitely an area where some optimizations
> > could be done.  I wouldn't want to do it until 2.5 though...
> 
> Actually, I did this for x86 last weekend :) Initial results are
> disappointing. 
> 
> It creates a special uncachable mapping and sits there
> zeroing pages in a low-priority thread (also tried
> doing it in the idle task).

Well if you are going to mess with caching make the mapping write-combining
on x86..  You get much better performance.

Eric

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