From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from userp2120.oracle.com ([156.151.31.85]:33776 "EHLO userp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726535AbeKNCVe (ORCPT ); Tue, 13 Nov 2018 21:21:34 -0500 Date: Tue, 13 Nov 2018 08:22:37 -0800 From: "Darrick J. Wong" To: Dave Chinner Cc: linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH 3/2] splice: increase pipe size in splice_direct_to_actor() Message-ID: <20181113162237.GF4235@magnolia> References: <20181108221909.27602-1-david@fromorbit.com> <20181109005410.GG19305@dastard> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181109005410.GG19305@dastard> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Fri, Nov 09, 2018 at 11:54:10AM +1100, Dave Chinner wrote: > > From: Dave Chinner > > When copy_file_range() is called on files that have been opened with > O_DIRECT, do_splice_direct() does a manual copy of the range one > pipe buffer at a time. The default is 16 pages, which means on > x86_64 it is limited to 64kB IO. This is extremely slow - 64k > synchrnous read/write will run at maybe 5-10MB/s on a spinning disk > and be seek bound. It will be faster on SSDs, but still very > inefficient. > > Increase the pipe size to the maximum allowed user size so that we > can get decent throughput for this highly sub-optimal copy loop. Add > a new function to the pipe code that lets us set the pipe size to > the maximum allowed without root permissions to keep things really > simple. We also don't care if changing the pipe size fails - that > will just result in a slower copy. > > Signed-off-by: Dave Chinner > --- > fs/pipe.c | 10 ++++++++++ > fs/splice.c | 7 +++++++ > include/linux/pipe_fs_i.h | 1 + > 3 files changed, 18 insertions(+) > > diff --git a/fs/pipe.c b/fs/pipe.c > index bdc5d3c0977d..436bc0464569 100644 > --- a/fs/pipe.c > +++ b/fs/pipe.c > @@ -1109,6 +1109,16 @@ static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg) > return ret; > } > > +/* > + * Set the pipe to the maximum allowable user size. Advisory only, will > + * swallow any errors and return the resultant pipe size. > + */ > +long pipe_set_max_safe_size(struct pipe_inode_info *pipe) > +{ > + pipe_set_size(pipe, pipe_max_size); > + return pipe->buffers * PAGE_SIZE; > +} > + > /* > * After the inode slimming patch, i_pipe/i_bdev/i_cdev share the same > * location, so checking ->i_pipe is not enough to verify that this is a > diff --git a/fs/splice.c b/fs/splice.c > index 3553f1956508..9749139da731 100644 > --- a/fs/splice.c > +++ b/fs/splice.c > @@ -931,6 +931,13 @@ ssize_t splice_direct_to_actor(struct file *in, struct splice_desc *sd, > current->splice_pipe = pipe; > } > > + /* > + * Try to increase the data holding capacity of the pipe so we can do > + * larger IOs. This may not increase the size at all because maximum > + * user pipe size is administrator controlled, but we still should try. > + */ > + pipe_set_max_safe_size(pipe); I get where you're going with this, but I have two questions: - Is it safe to be enlarging the pipe buffer size unconditionally? - Especially if we didn't just create the splice pipe? Suppose someone comes along later trying to splice things and doesn't realize the pipe is now 1MB... Then I started wondering about the splice_pipe lifetime and couldn't figure out if it ever gets detached from current prior to do_exit. I don't think it does, which means that we're stuck with the 1MB kernel memory allocation until the process dies. --D > + > /* > * Do the splice. > */ > diff --git a/include/linux/pipe_fs_i.h b/include/linux/pipe_fs_i.h > index 5a3bb3b7c9ad..962ba4cfcb74 100644 > --- a/include/linux/pipe_fs_i.h > +++ b/include/linux/pipe_fs_i.h > @@ -191,5 +191,6 @@ struct pipe_inode_info *get_pipe_info(struct file *file); > > int create_pipe_files(struct file **, int); > unsigned int round_pipe_size(unsigned long size); > +long pipe_set_max_safe_size(struct pipe_inode_info *pipe); > > #endif