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

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Date:	Wed, 25 Jun 2008 18:38:38 +0100
From:	Jamie Lokier <jamie@...reable.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Miklos Szeredi <miklos@...redi.hu>, jens.axboe@...cle.com,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.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()

Linus Torvalds wrote:
> I also really don't think this even fixes the problems you have with 
> FUSE/NFSD - because you'll still be reading zeroes for a truncated file. 
> Yes, you get the rigth counts, but you don't get the right data.
...
> That's "correct" from a splice() kind of standpoint (it's essentially a 
> temporary mmap() with MAP_PRIVATE), but the thing is, it just sounds like 
> the whole "page went away" thing is a more fundamental issue. It sounds 
> like nfds should hold a read-lock on the file while it has any IO in 
> flight, or something like that.

I'm thinking any kind of user-space server using splice() will not
want to transmit zeros either, when another process truncates the file.
E.g. Apache, Samba, etc.

Does this problem affect sendfile() users?

-- Jamie
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