Re: anon_vma RFC2

From: Rik van Riel
Date: Sat Mar 13 2004 - 12:32:19 EST

On Sat, 13 Mar 2004, Hugh Dickins wrote:
> On Sat, 13 Mar 2004, Linus Torvalds wrote:

> > if (PageAnonymous(page) && page->count > 1) {
> > newpage = alloc_page();
> > copy_page(page, newpage);
> > page = newpage;
> > }
> > /* Move the page to the new address */
> > page->index = address >> PAGE_SHIFT;
> >
> > and now we have zero special cases.
> That's always been a fallback solution, I was just a little too ashamed
> to propose it originally - seems a little wrong to waste whole pages
> rather than wasting a few bytes of data structure trying to track them:
> though the pages are pageable unlike any data structure we come up with.

No, Linus is right.

If a child process uses mremap(), it stands to reason that
it's about to use those pages for something.

Think of it as taking the COW faults early, because chances
are you'd be taking them anyway, just a little bit later...

"Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are,
by definition, not smart enough to debug it." - Brian W. Kernighan

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