Re: madvise on file pages

From: Andrew Morton (akpm@osdl.org)
Date: Thu Jul 31 2003 - 17:32:11 EST


"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.

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