linux-kernel - Re: [patch 1/2] mm: dont clear PG_uptodate in invalidate_complete

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Message-Id: <E1KBV7H-0005nv-Gl@pomaz-ex.szeredi.hu>
Date:	Wed, 25 Jun 2008 15:32:55 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	johnpol@....mipt.ru
CC:	miklos@...redi.hu, jens.axboe@...cle.com,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, hugh@...itas.com,
	nickpiggin@...oo.com.au
Subject: Re: [patch 1/2] mm: dont clear PG_uptodate in invalidate_complete_page2()

> > I haven't done an audit of all code that checks the PG_uptodate flags,
> > but I suspect, that this change won't have any harmful effects.  Most
> > code checks page->mapping to see if the page was truncated or
> > invalidated, before using it, and retries the find/read on the page if
> > it wasn't.  The page_cache_pipe_buf_confirm() code is an exception in
> > this regard.
> 
> What about writing path, when page is written after some previous write?

page->mapping should be checked in the write paths as well.

> Like __block_prepare_write()?

That's called with the page locked and page->mapping verified.

> > Signed-off-by: Miklos Szeredi <mszeredi@...e.cz>
> > ---
> >  mm/truncate.c |    1 -
> >  1 file changed, 1 deletion(-)
> > 
> > Index: linux-2.6/mm/truncate.c
> > ===================================================================
> > --- linux-2.6.orig/mm/truncate.c	2008-06-24 20:49:25.000000000 +0200
> > +++ linux-2.6/mm/truncate.c	2008-06-24 23:28:32.000000000 +0200
> > @@ -356,7 +356,6 @@ invalidate_complete_page2(struct address
> >  	BUG_ON(PagePrivate(page));
> >  	__remove_from_page_cache(page);
> >  	write_unlock_irq(&mapping->tree_lock);
> > -	ClearPageUptodate(page);
> >  	page_cache_release(page);	/* pagecache ref */
> >  	return 1;
> >  failed:
> 
> Don't do that, add new function instead which will do exactly that, if
> you do need exactly this behaviour.

I don't see any point in doing that.

> Also why isn't invalidate_complete_page() enough, if you want to have
> that page to be half invalidated?

I want the page fully invalidated, and I also want splice and nfs
exporting to work as for other filesystems.

Miklos
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