Re: statfs() / statvfs() syscall ballsup...

From: Andrew Morton <akpm@osdl.org>
To: trond.myklebust@fys.uio.no
Cc: torvalds@osdl.org, Joel.Becker@oracle.com,
	cfriesen@nortelnetworks.com, jamie@shareable.org,
	linux-kernel@vger.kernel.org
Subject: Re: statfs() / statvfs() syscall ballsup...
Date: Fri, 10 Oct 2003 19:53:43 -0700	[thread overview]
Message-ID: <20031010195343.6e821192.akpm@osdl.org> (raw)
In-Reply-To: <16262.62026.603149.157026@charged.uio.no>

Trond Myklebust <trond.myklebust@fys.uio.no> wrote:
>
> It does nothing for the case Joel mentioned where 2 different nodes
> are writing to the same device, and you need to force a read in order
> to resynchronize the page cache.
> Apart from O_DIRECT, we have nothing in the kernel as it stands that
> will allow userland to deal with this case.

Applications may use fadvise(POSIX_FADV_DONTNEED) to invalidate sections of
a file's pagecache.

It is not designed to be 100% reliable though: mmapped pages will be
retained, and dirty pages are skipped.

For the dirty pages it might be useful to add a new mode to fadvise which
syncs a section of a file's pages; -mm has the necessary infrastructure for
that.

POSIX does not define the fadvise() semantics very clearly, so it is largely
up to us to decide what makes sense.  There are a number of things which we
can do quite easily in there - it's mainly a matter of working out exactly
what we want to do.