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

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Message-Id: <E1KBWBK-0006Lp-03@pomaz-ex.szeredi.hu>
Date:	Wed, 25 Jun 2008 16:41:10 +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()

> > > Like __block_prepare_write()?
> > 
> > That's called with the page locked and page->mapping verified.
> 
> Only when called via standard codepath.

It would be a grave error to call it without the page lock.

> > I want the page fully invalidated, and I also want splice and nfs
> > exporting to work as for other filesystems.
> 
> Fully invalidated page can not be uptodate, doesnt' it? :)

That's just a question of how we interpret PG_uptodate.  If it means:
the page contains data that is valid, or was valid at some point in
time, then an invalidated or truncated page can be uptodate.

> You destroy existing functionality just because there are some obscure
> places, where it is used, so instead of fixing that places, you treat
> the symptom. After writing previous mail I found a way to workaround it
> even with your changes, but the whole approach of changing
> invalidate_complete_page2() is not correct imho.

You rely on page being !PageUptodate() after being invalidated?  Why
can't you check page->mapping instead (as everything else does)?

> Is this nfs/fuse problem you described:
> http://marc.info/?l=linux-fsdevel&m=121396920822693&w=2

Yes.

> Instead of returning error when reading from invalid page, now you
> return old content of it?

No, instead of returning a short count, it is now returning old
content.

Miklos
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