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

Rik van Riel
2001-03-20T19:35:51Z

On Tue, 20 Mar 2001, Andi Kleen wrote:
> On Tue, Mar 20, 2001 at 05:08:36PM +0100, Linus Torvalds 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.
> >
> > I don't think it's worth it. We should have basically zero contention on
> > this lock now, and adding complexity to try to release it sounds like a
> > bad idea when the only way to make contention on it is (a) kswapd (only
> > when paging stuff out) and (b) multiple threads (only when taking
> > concurrent page faults).
>
> Isn't (b) a rather common case in multi threaded applications ?

Multiple threads pagefaulting on the SAME page of anonymous
memory at the same time ?

I can imagine multiple threads pagefaulting on the same page
of some mmaped database, but on the same page of anonymous
memory ??

regards,

Rik
--
Virtual memory is like a game you can't win;
However, without VM there's truly nothing to lose...

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