Re: [patch 6/12] hold atomic kmaps across generic_file_read

Linus Torvalds
2002-08-10T16:58:09Z

On Sat, 10 Aug 2002, Rik van Riel wrote:
> On Sat, 10 Aug 2002, Linus Torvalds wrote:
>
> > and having it magically populate the VM directly with the whole file
> > mapping, with _one_ failed page fault. And the above is actually a fairly
> > common thing. See how many people have tried to optimize using mmap vs
> > read, and what they _all_ really wanted was this "populate the pages in
> > one go" thing.
>
> If this is worth it, chances are prefaulting at mmap() time
> could also be worth trying ... hmmm ;)

Maybe, maybe not.

The advantage of read() is that it contains an implicit "madvise()", since
the read _tells_ us that it wants X pages.

A page fault does not tell us, and prefaulting can hurt us.

Linus