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SubjectRe: clustering page-ins
On Thu, 29 Jul 1999, Jamie Lokier wrote:
> Chuck Lever wrote:
> > true. but i'm also worried about sharing the read-ahead information
> > amongst all mappers of a shared file. this case has come up in my
> > benchmarking (although i haven't tracked it down, it is occurring in some
> > basic commands that are run by the benchmark).
>
> Since each mapping has its own vm_area, I don't see the problem.
> Do you want different mappers to share read-ahead info?

yes, since they are sharing the same file in the same page cache it
would be silly to trigger read-ahead needlessly, even if it finds all the
pages already in the page cache.

> > so, i think the information needs to be in the file struct so that shared
> > maps don't continue to read ahead a file that is already in the page
> > cache.
>
> Sorry I don't quite understand what you want here. If you want to share
> read-ahead info between different mappers, struct file isn't going to do
> it -- each new open() creates a new struct file. If you don't, vm_area
> and struct file won't make much difference.

> It's only when you consider multiple mappings made from the same file
> descriptor (or passed through fork/exec) that there's a difference: then
> struct file leads to sharing while vm_area does not. There's also the
> matter of files mapped and read with read() (e.g. ELF executables).

so perhaps a better place to put read-ahead context is in the file's
inode.

- Chuck Lever
--
corporate: <chuckl@netscape.com>
personal: <chucklever@netscape.net> or <cel@monkey.org>

The Linux Scalability project:
http://www.citi.umich.edu/projects/linux-scalability/


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