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From: Al Viro <viro@ZenIV.linux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Dave Chinner <david@fromorbit.com>, CAI Qian <caiqian@redhat.com>,
	linux-xfs <linux-xfs@vger.kernel.org>,
	xfs@oss.sgi.com, Jens Axboe <axboe@kernel.dk>,
	Nick Piggin <npiggin@gmail.com>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: [PATCH 12/12] switch default_file_splice_read() to use of pipe-backed iov_iter
Date: Sat, 24 Sep 2016 05:02:26 +0100
Message-ID: <20160924040226.GR2356@ZenIV.linux.org.uk> (raw)
In-Reply-To: <CA+55aFyr-X_6FcWkSXBUcxV0p1BUZw8d=46wawv2x+8y7f8YcQ@mail.gmail.com>

we only use iov_iter_get_pages_alloc() and iov_iter_advance() -
pages are filled by kernel_readv() via a kvec array (as we used
to do all along), so iov_iter here is used only as a way of
arranging for those pages to be in pipe.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 fs/splice.c | 111 ++++++++++++++++++++++--------------------------------------
 1 file changed, 40 insertions(+), 71 deletions(-)

diff --git a/fs/splice.c b/fs/splice.c
index 58c322a..0df907b 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -361,7 +361,7 @@ const struct pipe_buf_operations nosteal_pipe_buf_ops = {
 };
 EXPORT_SYMBOL(nosteal_pipe_buf_ops);
 
-static ssize_t kernel_readv(struct file *file, const struct iovec *vec,
+static ssize_t kernel_readv(struct file *file, const struct kvec *vec,
 			    unsigned long vlen, loff_t offset)
 {
 	mm_segment_t old_fs;
@@ -397,96 +397,65 @@ static ssize_t default_file_splice_read(struct file *in, loff_t *ppos,
 				 struct pipe_inode_info *pipe, size_t len,
 				 unsigned int flags)
 {
+	struct kvec *vec, __vec[PIPE_DEF_BUFFERS];
+	struct iov_iter to;
+	struct page **pages;
 	unsigned int nr_pages;
-	unsigned int nr_freed;
-	size_t offset;
-	struct page *pages[PIPE_DEF_BUFFERS];
-	struct partial_page partial[PIPE_DEF_BUFFERS];
-	struct iovec *vec, __vec[PIPE_DEF_BUFFERS];
+	size_t offset, dummy, copied = 0;
 	ssize_t res;
-	size_t this_len;
-	int error;
 	int i;
-	struct splice_pipe_desc spd = {
-		.pages = pages,
-		.partial = partial,
-		.nr_pages_max = PIPE_DEF_BUFFERS,
-		.flags = flags,
-		.ops = &default_pipe_buf_ops,
-		.spd_release = spd_release_page,
-	};
 
-	if (splice_grow_spd(pipe, &spd))
+	if (pipe->nrbufs == pipe->buffers)
+		return -EAGAIN;
+
+	/*
+	 * Try to keep page boundaries matching to source pagecache ones -
+	 * it probably won't be much help, but...
+	 */
+	offset = *ppos & ~PAGE_MASK;
+
+	iov_iter_pipe(&to, ITER_PIPE | READ, pipe, len + offset);
+
+	res = iov_iter_get_pages_alloc(&to, &pages, len + offset, &dummy);
+	if (res <= 0)
 		return -ENOMEM;
 
-	res = -ENOMEM;
+	nr_pages = res / PAGE_SIZE;
+
 	vec = __vec;
-	if (spd.nr_pages_max > PIPE_DEF_BUFFERS) {
-		vec = kmalloc(spd.nr_pages_max * sizeof(struct iovec), GFP_KERNEL);
-		if (!vec)
-			goto shrink_ret;
+	if (nr_pages > PIPE_DEF_BUFFERS) {
+		vec = kmalloc(nr_pages * sizeof(struct kvec), GFP_KERNEL);
+		if (unlikely(!vec)) {
+			res = -ENOMEM;
+			goto out;
+		}
 	}
 
-	offset = *ppos & ~PAGE_MASK;
-	nr_pages = (len + offset + PAGE_SIZE - 1) >> PAGE_SHIFT;
-
-	for (i = 0; i < nr_pages && i < spd.nr_pages_max && len; i++) {
-		struct page *page;
-
-		page = alloc_page(GFP_USER);
-		error = -ENOMEM;
-		if (!page)
-			goto err;
+	pipe->bufs[to.idx].offset = offset;
+	pipe->bufs[to.idx].len -= offset;
 
-		this_len = min_t(size_t, len, PAGE_SIZE - offset);
-		vec[i].iov_base = (void __user *) page_address(page);
+	for (i = 0; i < nr_pages; i++) {
+		size_t this_len = min_t(size_t, len, PAGE_SIZE - offset);
+		vec[i].iov_base = page_address(pages[i]) + offset;
 		vec[i].iov_len = this_len;
-		spd.pages[i] = page;
-		spd.nr_pages++;
 		len -= this_len;
 		offset = 0;
 	}
 
-	res = kernel_readv(in, vec, spd.nr_pages, *ppos);
-	if (res < 0) {
-		error = res;
-		goto err;
-	}
-
-	error = 0;
-	if (!res)
-		goto err;
-
-	nr_freed = 0;
-	for (i = 0; i < spd.nr_pages; i++) {
-		this_len = min_t(size_t, vec[i].iov_len, res);
-		spd.partial[i].offset = 0;
-		spd.partial[i].len = this_len;
-		if (!this_len) {
-			__free_page(spd.pages[i]);
-			spd.pages[i] = NULL;
-			nr_freed++;
-		}
-		res -= this_len;
-	}
-	spd.nr_pages -= nr_freed;
-
-	res = splice_to_pipe(pipe, &spd);
-	if (res > 0)
+	res = kernel_readv(in, vec, nr_pages, *ppos);
+	if (res > 0) {
+		copied = res;
 		*ppos += res;
+	}
 
-shrink_ret:
 	if (vec != __vec)
 		kfree(vec);
-	splice_shrink_spd(&spd);
+out:
+	for (i = 0; i < nr_pages; i++)
+		put_page(pages[i]);
+	kvfree(pages);
+	iov_iter_advance(&to, copied);	/* truncates and discards */
 	return res;
-
-err:
-	for (i = 0; i < spd.nr_pages; i++)
-		__free_page(spd.pages[i]);
-
-	res = error;
-	goto shrink_ret;
 }
 
 /*
-- 
2.9.3


  parent reply index

Thread overview: 101+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20160908235521.GL2356@ZenIV.linux.org.uk>
     [not found] ` <20160909015324.GD30056@dastard>
     [not found]   ` <CA+55aFzohsUXj_3BeFNr2t50Wm=G+7toRDEz=Tk7VJqP3n1hXQ@mail.gmail.com>
     [not found]     ` <CA+55aFxrqCng2Qxasc9pyMrKUGFjo==fEaFT1vkH9Lncte3RgQ@mail.gmail.com>
     [not found]       ` <20160909023452.GO2356@ZenIV.linux.org.uk>
     [not found]         ` <CA+55aFwHQMjO4-vtfB9-ytc=o+DRo-HXVGckvXLboUxgpwb7_g@mail.gmail.com>
     [not found]           ` <20160909221945.GQ2356@ZenIV.linux.org.uk>
     [not found]             ` <CA+55aFzTOOB6oEVaaGD0N7Uznk-W9+ULPwzsxS_L_oZqGVSeLA@mail.gmail.com>
     [not found]               ` <20160914031648.GB2356@ZenIV.linux.org.uk>
     [not found]                 ` <20160914133925.2fba4629@roar.ozlabs.ibm.com>
2016-09-18  5:33                   ` xfs_file_splice_read: possible circular locking dependency detected Al Viro
2016-09-19  3:08                     ` Nicholas Piggin
2016-09-19  6:11                       ` Al Viro
2016-09-19  7:26                         ` Nicholas Piggin
     [not found]                 ` <CA+55aFznQaOWoSMNphgGJJWZ=8-odrc0DAUMzfGPQe+_N4UgNA@mail.gmail.com>
     [not found]                   ` <20160914042559.GC2356@ZenIV.linux.org.uk>
     [not found]                     ` <20160917082007.GA6489@ZenIV.linux.org.uk>
     [not found]                       ` <20160917190023.GA8039@ZenIV.linux.org.uk>
2016-09-18 19:31                         ` skb_splice_bits() and large chunks in pipe (was " Al Viro
2016-09-18 20:12                           ` Linus Torvalds
2016-09-18 22:31                             ` Al Viro
2016-09-19  0:18                               ` Linus Torvalds
2016-09-23 19:00                         ` [RFC][CFT] splice_read reworked Al Viro
2016-09-23 19:01                           ` [PATCH 01/11] fix memory leaks in tracing_buffers_splice_read() Al Viro
2016-09-23 19:02                           ` [PATCH 02/11] splice_to_pipe(): don't open-code wakeup_pipe_readers() Al Viro
2016-09-23 19:02                           ` [PATCH 03/11] splice: switch get_iovec_page_array() to iov_iter Al Viro
2016-09-23 19:03                           ` [PATCH 04/11] splice: lift pipe_lock out of splice_to_pipe() Al Viro
2016-09-23 19:45                             ` Linus Torvalds
2016-09-23 20:10                               ` Al Viro
2016-09-23 20:36                                 ` Linus Torvalds
2016-09-24  3:59                                   ` Al Viro
2016-09-24 17:29                                     ` Al Viro
2016-09-27 15:38                                       ` Nicholas Piggin
2016-09-27 15:53                                       ` Chuck Lever
2016-09-24  3:59                                   ` [PATCH 04/12] " Al Viro
2016-09-26 13:35                                     ` Miklos Szeredi
2016-09-27  4:14                                       ` Al Viro
2016-12-17 19:54                                     ` Andreas Schwab
2016-12-18 19:28                                       ` Linus Torvalds
2016-12-18 19:57                                         ` Andreas Schwab
2016-12-18 20:12                                         ` Al Viro
2016-12-18 20:30                                           ` Al Viro
2016-12-18 22:10                                             ` Linus Torvalds
2016-12-18 22:18                                               ` Al Viro
2016-12-18 22:22                                                 ` Linus Torvalds
2016-12-18 22:49                                               ` Andreas Schwab
2016-12-21 18:56                                               ` Andreas Schwab
2016-12-21 19:12                                                 ` Linus Torvalds
2016-09-24  4:00                                   ` [PATCH 06/12] new helper: add_to_pipe() Al Viro
2016-09-26 13:49                                     ` Miklos Szeredi
2016-09-24  4:01                                   ` [PATCH 10/12] new iov_iter flavour: pipe-backed Al Viro
2016-09-29 20:53                                     ` Miklos Szeredi
2016-09-29 22:50                                       ` Al Viro
2016-09-30  7:30                                         ` Miklos Szeredi
2016-10-03  3:34                                           ` [RFC] O_DIRECT vs EFAULT (was Re: [PATCH 10/12] new iov_iter flavour: pipe-backed) Al Viro
2016-10-03 17:07                                             ` Linus Torvalds
2016-10-03 18:54                                               ` Al Viro
2016-09-24  4:01                                   ` [PATCH 11/12] switch generic_file_splice_read() to use of ->read_iter() Al Viro
2016-09-24  4:02                                   ` Al Viro [this message]
2016-09-23 19:03                           ` [PATCH 05/11] skb_splice_bits(): get rid of callback Al Viro
2016-09-23 19:04                           ` [PATCH 06/11] new helper: add_to_pipe() Al Viro
2016-09-23 19:04                           ` [PATCH 07/11] fuse_dev_splice_read(): switch to add_to_pipe() Al Viro
2016-09-23 19:06                           ` [PATCH 08/11] cifs: don't use memcpy() to copy struct iov_iter Al Viro
2016-09-23 19:08                           ` [PATCH 09/11] fuse_ioctl_copy_user(): don't open-code copy_page_{to,from}_iter() Al Viro
2016-09-26  9:31                             ` Miklos Szeredi
2016-09-23 19:09                           ` [PATCH 10/11] new iov_iter flavour: pipe-backed Al Viro
2016-09-23 19:10                           ` [PATCH 11/11] switch generic_file_splice_read() to use of ->read_iter() Al Viro
2016-09-30 13:32                           ` [RFC][CFT] splice_read reworked CAI Qian
2016-09-30 17:42                             ` CAI Qian
2016-09-30 18:33                               ` CAI Qian
2016-10-03  1:37                                 ` Al Viro
2016-10-03 17:49                                   ` CAI Qian
2016-10-04 17:39                                     ` local DoS - systemd hang or timeout (WAS: Re: [RFC][CFT] splice_read reworked) CAI Qian
2016-10-04 21:42                                       ` tj
2016-10-05 14:09                                         ` CAI Qian
2016-10-05 15:30                                           ` tj
2016-10-05 15:54                                             ` CAI Qian
2016-10-05 18:57                                               ` CAI Qian
2016-10-05 20:05                                                 ` Al Viro
2016-10-06 12:20                                                   ` CAI Qian
2016-10-06 12:25                                                     ` CAI Qian
2016-10-06 16:11                                                       ` CAI Qian
2016-10-06 17:00                                                         ` Linus Torvalds
2016-10-06 18:12                                                           ` CAI Qian
2016-10-07  9:57                                                           ` Dave Chinner
2016-10-07 15:25                                                             ` Linus Torvalds
2016-10-07  7:08                                                       ` Jan Kara
2016-10-07 14:43                                                         ` CAI Qian
2016-10-07 15:27                                                           ` CAI Qian
2016-10-07 18:56                                                             ` CAI Qian
2016-10-09 21:54                                                               ` Dave Chinner
2016-10-10 14:10                                                                 ` CAI Qian
2016-10-10 20:14                                                                   ` CAI Qian
2016-10-10 21:57                                                                   ` Dave Chinner
2016-10-12 19:50                                                                     ` [bisected] " CAI Qian
2016-10-12 20:59                                                                       ` Dave Chinner
2016-10-13 16:25                                                                         ` CAI Qian
2016-10-13 20:49                                                                           ` Dave Chinner
2016-10-13 20:56                                                                             ` CAI Qian
2016-10-09 21:51                                                           ` Dave Chinner
2016-10-21 15:38                                                         ` [4.9-rc1+] overlayfs lockdep CAI Qian
2016-10-24 12:57                                                           ` Miklos Szeredi
2016-10-07  9:27                                                     ` local DoS - systemd hang or timeout (WAS: Re: [RFC][CFT] splice_read reworked) Dave Chinner
2016-10-03  1:42                               ` [RFC][CFT] splice_read reworked Al Viro
2016-10-03 14:06                                 ` CAI Qian
2016-10-03 15:20                                   ` CAI Qian
2016-10-03 21:12                                     ` Dave Chinner
2016-10-04 13:57                                       ` CAI Qian
2016-10-03 20:32                                   ` CAI Qian
2016-10-03 20:35                                     ` Al Viro
2016-10-04 13:29                                       ` CAI Qian
2016-10-04 14:28                                         ` Al Viro
2016-10-04 16:21                                           ` CAI Qian
2016-10-04 20:12                                             ` Al Viro
2016-10-05 14:30                                               ` CAI Qian
2016-10-05 16:07                                                 ` Al Viro
2016-09-19  0:22 skb_splice_bits() and large chunks in pipe (was Re: xfs_file_splice_read: possible circular locking dependency detected Al Viro
2016-09-20  9:51 ` Herbert Xu

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