Re: [BK PATCH 2.5] Introduce 64-bit versions of

[Andrew Morton]

Russell King wrote:
> 
> On Sun, Jul 28, 2002 at 05:10:48PM -0700, Andrew Morton wrote:
> > - Remove ->virtual, do page_address() via a hash.  4(ish) bytes saved.
> 
> Hmmmmmmm.  page_address() is already 5 loads (on ARM) if page->virtual
> isn't used.  I'm seriously considering changing page_address() to cover
> the 3 cases more efficiently:

Well, one would want to keep the WANT_PAGE_VIRTUAL thing anyway.

btw, the usage of page_address() will quite possibly drop sharply soon
anyway.  There's the patch floating about which permits atomic
kmaps to be held across copy_*_user.  If that is adopted, things
like the pagecache IO routines won't do page_address() any more.

Said patch speeds up pagecache IO by between 0% and probably 30%.
It's the mystery surrounding this variation which is holding things
up.

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