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

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Date:	Tue, 24 Jun 2008 10:04:41 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, torvalds@...ux-foundation.org
Subject: Re: [rfc patch 3/4] splice: remove confirm from pipe_buf_operations

On Sat, Jun 21 2008, Miklos Szeredi wrote:
> From: Miklos Szeredi <mszeredi@...e.cz>
> 
> The 'confirm' operation was only used for splicing from page cache, to
> wait for read on a page to finish.  But generic_file_splice_read()
> already blocks on readahead reads, so it seems logical to block on the
> rare and slow single page reads too.
> 
> So wait for readpage to finish inside __generic_file_splice_read() and
> remove the 'confirm' method.
> 
> This also fixes short return counts when the filesystem (e.g. fuse)
> invalidates the page between insertation and removal.

One of the basic goals of splice is to allow the pipe buffer to only be
consisten when a consumer asks for it, otherwise the filling will always
be sync. There should be no blocking on reads in the splice-in path,
only on consumption for splice-out.

So nack on this one, too.

-- 
Jens Axboe

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