madvise on file pages

madvise on file pages

[Muthian S]

Hi,

Could someone inform as to what is the behavior when madvise DONTNEED is 
called on pages that are mmap'd from local files mapped with MAP_SHARED, 
i.e. they share the same page that the file cache does.  In such cases, can 
madvise be made to release specific pages in the file cache by mmap-ing the 
relevant file segment ?

thanks,
Muthian.

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Re: madvise on file pages

[Andrew Morton]

"Muthian S" <muthian_s@hotmail.com> wrote:
>
> Hi,
> 
> Could someone inform as to what is the behavior when madvise DONTNEED is 
> called on pages that are mmap'd from local files mapped with MAP_SHARED, 
> i.e. they share the same page that the file cache does.

The pages are unmapped from the calling process's pagetables.  We don't
actually free the physical pages.

> In such cases, can 
> madvise be made to release specific pages in the file cache by mmap-ing the 
> relevant file segment ?

No.

2.6 kernels implement the fadvise() syscall (accessible by glibc's
posix_fadvise() function) which will do this.

Re: madvise on file pages

[Antonio Vargas]

On Thu, Jul 31, 2003 at 03:32:11PM -0700, Andrew Morton wrote:
> "Muthian S" <muthian_s@hotmail.com> wrote:
> >
> > Hi,
> > 
> > Could someone inform as to what is the behavior when madvise DONTNEED is 
> > called on pages that are mmap'd from local files mapped with MAP_SHARED, 
> > i.e. they share the same page that the file cache does.
> 
> The pages are unmapped from the calling process's pagetables.  We don't
> actually free the physical pages.
> 
> > In such cases, can 
> > madvise be made to release specific pages in the file cache by mmap-ing the 
> > relevant file segment ?
> 
> No.
> 
> 2.6 kernels implement the fadvise() syscall (accessible by glibc's
> posix_fadvise() function) which will do this.

Perhaps we could send the page to the least-used end of the page lists?

-- 
winden/network

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