linux-kernel - Re: [rfc patch 3/4] splice: remove confirm from pipe_buf

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Message-Id: <E1KBE7p-0002eT-CJ@pomaz-ex.szeredi.hu>
Date:	Tue, 24 Jun 2008 21:24:21 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	torvalds@...ux-foundation.org
CC:	miklos@...redi.hu, jens.axboe@...cle.com,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [rfc patch 3/4] splice: remove confirm from
 pipe_buf_operations

> > 
> > Let's start with page_cache_pipe_buf_confirm().  How should we deal
> > with finding an invalidated page (!PageUptodate(page) &&
> > !page->mapping)?
> 
> I suspect we just have to use it. After all, it was valid when the read 
> was done. The fact that it got invalidated later is kind of immaterial.

Right.  But what if it's invalidated *before* becoming uptodate (if
you'd read my mail further, I discussed this).

Why does invalidate_complete_page2() do ClearPageUptodate()?  Dunno,
maybe it shoulnd't.  But that would need a rather thorough audit of
all code checking PageUptodate()...

> splice() is an optimized read+write. The read reads it into a temporary 
> buffer. The fact that it's a zero-copy buffer and basically just re-uses 
> the source doesn't really change that.

Agreed.

Miklos
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