Date:	Tue, 1 Aug 2006 12:14:58 -0700
From:	"Nate Diller" <nate.diller@...il.com>
To:	"Andrew Morton" <akpm@...l.org>
Cc:	"Vladimir V. Saveliev" <vs@...esys.com>, vda.linux@...glemail.com,
	linux-kernel@...r.kernel.org, Reiserfs-List@...esys.com
Subject: Re: reiser4: maybe just fix bugs?

On 8/1/06, Andrew Morton <akpm@...l.org> wrote:
> On Tue, 01 Aug 2006 15:24:37 +0400
> "Vladimir V. Saveliev" <vs@...esys.com> wrote:
>
> > > >The writeout code is ugly, although that's largely due to a mismatch between
> > > >what reiser4 wants to do and what the VFS/MM expects it to do.
> >
> > Yes. reiser4 writeouts atoms. Most of pages get into atoms via
> > sys_write. But pages dirtied via shared mapping do not. They get into
> > atoms in reiser4's writepages address space operation.
>
> It think you mean ->writepage - reiser4 desn't implement ->writepages().
>
> I assume you considered hooking into ->set_page_dirty() to do the
> add-to-atom thing earlier on?
>
> We'll merge mm-tracking-shared-dirty-pages.patch into 2.6.19-rc1, which
> would make that approach considerably more successful, I expect.
> ->set_page_dirty() is a bit awkward because it can be called under
> spinlock.
>
> Maybe comething could also be gained from the new
> vm_operations_struct.page_mkwrite(), although that's less obvious...
>
> > That is why
> > reiser4_sync_inodes has two steps: on first one it calls
> > generic_sync_sb_inodes to call writepages for dirty inodes to capture
> > pages dirtied via shared mapping into atoms. Second step flushes atoms.
> >
> > > >
> > > I agree --- both with it being ugly, and that being part of why.
> > >
> > > >  If it
> > > >works, we can live with it, although perhaps the VFS could be made smarter.
> > > >
> > > >
> > > I would be curious regarding any ideas on that.  Next time I read
> > > through that code, I will keep in mind that you are open to making VFS
> > > changes if it improves things, and I will try to get clever somehow and
> > > send it by you.  Our squalloc code though is I must say the most
> > > complicated and ugliest piece of code I ever worked on for which every
> > > cumulative ugliness had a substantive performance advantage requiring us
> > > to keep it.  If you spare yourself from reading that, it is
> > > understandable to do so.
> > >
> > > >I'd say that resier4's major problem is the lack of xattrs, acls and
> > > >direct-io.  That's likely to significantly limit its vendor uptake.
> >
> > xattrs is really a problem.
>
> That's not good.  The ability to properly support SELinux is likely to be
> important.

i disagreee that it will be difficult.  unfortunately, the patch that
I am working on right now, which fixes the various reiser4 specific
functions to avoid using VFS data structures unless needed, is a
prerequisite to enabling xattrs.  creating it is a time of tedium for
me, and it will cause a bit of internal churn (1000 lines and
counting).  it's all in the fs/reiser4 directory though, and it should
cause minimal disruption, as far as runtime bugs introduced.

once that's taken care of, i will be delighted to enable xattr support
in a way that will make selinux and beagle and such run as expected,
and will have the added advantage of some major scalability
improvements for certain lookup and update operations.

NATE
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