[PATCH][RFC] dynamic pipe resizing

[Jens Axboe <jens.axboe@oracle.com>]

Hi,

Dabbling around with splice a bit, I added some code to change the size
of a pipe. Currently it's hardcoded as 16 pages, with this patch you can
shrink (if you wanted) or grow (the likely scenario) if you want to
increase the size of your in-kernel buffer for splice operations.

Like with my original splice patches from 2005, I used fcntl()
F_GETPIPE_SZ and F_SETPIPE_SZ to change the size of the pipe. I'm not
particularly fond of that interface, so suggestions on how to improve it
would be appreciated. Even if fcntl() should be the preferred approach,
I think it would be better to pass in a byte based value instead of a
number of pages.

diff --git a/fs/fcntl.c b/fs/fcntl.c
index 78b2ff0..c4571fc 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -18,6 +18,7 @@
 #include <linux/ptrace.h>
 #include <linux/signal.h>
 #include <linux/rcupdate.h>
+#include <linux/pipe_fs_i.h>
 
 #include <asm/poll.h>
 #include <asm/siginfo.h>
@@ -376,6 +377,10 @@ static long do_fcntl(int fd, unsigned int cmd, unsigned long arg,
 	case F_NOTIFY:
 		err = fcntl_dirnotify(fd, filp, arg);
 		break;
+	case F_SETPIPE_SZ:
+	case F_GETPIPE_SZ:
+		err = pipe_fcntl(filp, cmd, arg);
+		break;
 	default:
 		break;
 	}
diff --git a/fs/pipe.c b/fs/pipe.c
index 6b3d91a..734ede4 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -342,7 +342,7 @@ redo:
 			if (!buf->len) {
 				buf->ops = NULL;
 				ops->release(pipe, buf);
-				curbuf = (curbuf + 1) & (PIPE_BUFFERS-1);
+				curbuf = (curbuf + 1) & (pipe->buffers - 1);
 				pipe->curbuf = curbuf;
 				pipe->nrbufs = --bufs;
 				do_wakeup = 1;
@@ -424,7 +424,7 @@ pipe_write(struct kiocb *iocb, const struct iovec *_iov,
 	chars = total_len & (PAGE_SIZE-1); /* size of the last buffer */
 	if (pipe->nrbufs && chars != 0) {
 		int lastbuf = (pipe->curbuf + pipe->nrbufs - 1) &
-							(PIPE_BUFFERS-1);
+							(pipe->buffers - 1);
 		struct pipe_buffer *buf = pipe->bufs + lastbuf;
 		const struct pipe_buf_operations *ops = buf->ops;
 		int offset = buf->offset + buf->len;
@@ -470,8 +470,8 @@ redo1:
 			break;
 		}
 		bufs = pipe->nrbufs;
-		if (bufs < PIPE_BUFFERS) {
-			int newbuf = (pipe->curbuf + bufs) & (PIPE_BUFFERS-1);
+		if (bufs < pipe->buffers) {
+			int newbuf = (pipe->curbuf + bufs) & (pipe->buffers-1);
 			struct pipe_buffer *buf = pipe->bufs + newbuf;
 			struct page *page = pipe->tmp_page;
 			char *src;
@@ -532,7 +532,7 @@ redo2:
 			if (!total_len)
 				break;
 		}
-		if (bufs < PIPE_BUFFERS)
+		if (bufs < pipe->buffers)
 			continue;
 		if (filp->f_flags & O_NONBLOCK) {
 			if (!ret)
@@ -594,7 +594,7 @@ pipe_ioctl(struct inode *pino, struct file *filp,
 			nrbufs = pipe->nrbufs;
 			while (--nrbufs >= 0) {
 				count += pipe->bufs[buf].len;
-				buf = (buf+1) & (PIPE_BUFFERS-1);
+				buf = (buf+1) & (pipe->buffers - 1);
 			}
 			mutex_unlock(&inode->i_mutex);
 
@@ -625,7 +625,7 @@ pipe_poll(struct file *filp, poll_table *wait)
 	}
 
 	if (filp->f_mode & FMODE_WRITE) {
-		mask |= (nrbufs < PIPE_BUFFERS) ? POLLOUT | POLLWRNORM : 0;
+		mask |= (nrbufs < pipe->buffers) ? POLLOUT | POLLWRNORM : 0;
 		/*
 		 * Most Unices do not set POLLERR for FIFOs but on Linux they
 		 * behave exactly like pipes for poll().
@@ -860,25 +860,32 @@ struct pipe_inode_info * alloc_pipe_info(struct inode *inode)
 
 	pipe = kzalloc(sizeof(struct pipe_inode_info), GFP_KERNEL);
 	if (pipe) {
-		init_waitqueue_head(&pipe->wait);
-		pipe->r_counter = pipe->w_counter = 1;
-		pipe->inode = inode;
+		pipe->bufs = kzalloc(sizeof(struct pipe_buffer) * PIPE_DEF_BUFFERS, GFP_KERNEL);
+		if (pipe->bufs) {
+			init_waitqueue_head(&pipe->wait);
+			pipe->r_counter = pipe->w_counter = 1;
+			pipe->inode = inode;
+			pipe->buffers = PIPE_DEF_BUFFERS;
+			return pipe;
+		}
+		kfree(pipe);
 	}
 
-	return pipe;
+	return NULL;
 }
 
 void __free_pipe_info(struct pipe_inode_info *pipe)
 {
 	int i;
 
-	for (i = 0; i < PIPE_BUFFERS; i++) {
+	for (i = 0; i < pipe->buffers; i++) {
 		struct pipe_buffer *buf = pipe->bufs + i;
 		if (buf->ops)
 			buf->ops->release(pipe, buf);
 	}
 	if (pipe->tmp_page)
 		__free_page(pipe->tmp_page);
+	kfree(pipe->bufs);
 	kfree(pipe);
 }
 
@@ -1077,6 +1084,81 @@ int do_pipe(int *fd)
 }
 
 /*
+ * Allocate a new array of pipe buffers and copy the info over. Returns the
+ * pipe size if successful, or return -ERROR on error.
+ */
+static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg)
+{
+	struct pipe_buffer *bufs;
+
+	/*
+	 * Must be a power-of-2 current
+	 */
+	if (arg & (arg - 1))
+		return -EINVAL;
+
+	/*
+	 * We can shrink the pipe, if arg >= pipe->nrbufs. Since we don't
+	 * expect a lot of shrink+grow operations, just free and allocate
+	 * again like we would do for growing. If the pipe currently
+	 * contains more buffers than arg, then return busy.
+	 */
+	if (arg < pipe->nrbufs)
+		return -EBUSY;
+
+	bufs = kzalloc(arg * sizeof(struct pipe_buffer), GFP_KERNEL);
+	if (unlikely(!bufs))
+		return -ENOMEM;
+
+	/*
+	 * The pipe array wraps around, so just start the new one at zero
+	 * and adjust the indexes.
+	 */
+	if (pipe->nrbufs) {
+		const unsigned int tail = pipe->nrbufs & (pipe->buffers - 1);
+		const unsigned int head = pipe->nrbufs - tail;
+
+		if (head)
+			memcpy(bufs, pipe->bufs + pipe->curbuf, head * sizeof(struct pipe_buffer));
+		if (tail)
+			memcpy(bufs + head, pipe->bufs + pipe->curbuf, tail * sizeof(struct pipe_buffer));
+	}
+
+	pipe->curbuf = 0;
+	kfree(pipe->bufs);
+	pipe->bufs = bufs;
+	pipe->buffers = arg;
+	return arg;
+}
+
+long pipe_fcntl(struct file *file, unsigned int cmd, unsigned long arg)
+{
+	struct pipe_inode_info *pipe;
+	long ret;
+
+	pipe = file->f_path.dentry->d_inode->i_pipe;
+	if (!pipe)
+		return -EBADF;
+
+	mutex_lock(&pipe->inode->i_mutex);
+
+	switch (cmd) {
+	case F_SETPIPE_SZ:
+		ret = pipe_set_size(pipe, arg);
+		break;
+	case F_GETPIPE_SZ:
+		ret = pipe->buffers;
+		break;
+	default:
+		ret = -EINVAL;
+		break;
+	}
+
+	mutex_unlock(&pipe->inode->i_mutex);
+	return ret;
+}
+
+/*
  * pipefs should _never_ be mounted by userland - too much of security hassle,
  * no real gain from having the whole whorehouse mounted. So we don't need
  * any operations on the root directory. However, we need a non-trivial
diff --git a/fs/splice.c b/fs/splice.c
index c010a72..e6799ac 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -190,8 +190,8 @@ ssize_t splice_to_pipe(struct pipe_inode_info *pipe,
 			break;
 		}
 
-		if (pipe->nrbufs < PIPE_BUFFERS) {
-			int newbuf = (pipe->curbuf + pipe->nrbufs) & (PIPE_BUFFERS - 1);
+		if (pipe->nrbufs < pipe->buffers) {
+			int newbuf = (pipe->curbuf + pipe->nrbufs) & (pipe->buffers - 1);
 			struct pipe_buffer *buf = pipe->bufs + newbuf;
 
 			buf->page = spd->pages[page_nr];
@@ -211,7 +211,7 @@ ssize_t splice_to_pipe(struct pipe_inode_info *pipe,
 
 			if (!--spd->nr_pages)
 				break;
-			if (pipe->nrbufs < PIPE_BUFFERS)
+			if (pipe->nrbufs < pipe->buffers)
 				continue;
 
 			break;
@@ -259,6 +259,36 @@ ssize_t splice_to_pipe(struct pipe_inode_info *pipe,
 	return ret;
 }
 
+/*
+ * Check if we need to grow the arrays holding pages and partial page
+ * descriptions.
+ */
+int splice_grow_spd(struct pipe_inode_info *pipe, struct splice_pipe_desc *spd)
+{
+	if (pipe->buffers <= PIPE_DEF_BUFFERS)
+		return 0;
+
+	spd->pages = kmalloc(pipe->buffers * sizeof(struct page *), GFP_KERNEL);
+	spd->partial = kmalloc(pipe->buffers * sizeof(struct partial_page), GFP_KERNEL);
+
+	if (spd->pages && spd->partial)
+		return 0;
+
+	kfree(spd->pages);
+	kfree(spd->partial);
+	return -ENOMEM;
+}
+
+void splice_shrink_spd(struct pipe_inode_info *pipe,
+		       struct splice_pipe_desc *spd)
+{
+	if (pipe->buffers <= PIPE_DEF_BUFFERS)
+		return;
+
+	kfree(spd->pages);
+	kfree(spd->partial);
+}
+
 static int
 __generic_file_splice_read(struct file *in, loff_t *ppos,
 			   struct pipe_inode_info *pipe, size_t len,
@@ -266,8 +296,8 @@ __generic_file_splice_read(struct file *in, loff_t *ppos,
 {
 	struct address_space *mapping = in->f_mapping;
 	unsigned int loff, nr_pages, req_pages;
-	struct page *pages[PIPE_BUFFERS];
-	struct partial_page partial[PIPE_BUFFERS];
+	struct page *pages[PIPE_DEF_BUFFERS];
+	struct partial_page partial[PIPE_DEF_BUFFERS];
 	struct page *page;
 	pgoff_t index, end_index;
 	loff_t isize;
@@ -279,15 +309,18 @@ __generic_file_splice_read(struct file *in, loff_t *ppos,
 		.ops = &page_cache_pipe_buf_ops,
 	};
 
+	if (splice_grow_spd(pipe, &spd))
+		return -ENOMEM;
+
 	index = *ppos >> PAGE_CACHE_SHIFT;
 	loff = *ppos & ~PAGE_CACHE_MASK;
 	req_pages = (len + loff + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
-	nr_pages = min(req_pages, (unsigned)PIPE_BUFFERS);
+	nr_pages = min(req_pages, pipe->buffers);
 
 	/*
 	 * Lookup the (hopefully) full range of pages we need.
 	 */
-	spd.nr_pages = find_get_pages_contig(mapping, index, nr_pages, pages);
+	spd.nr_pages = find_get_pages_contig(mapping, index, nr_pages, spd.pages);
 	index += spd.nr_pages;
 
 	/*
@@ -328,7 +361,7 @@ __generic_file_splice_read(struct file *in, loff_t *ppos,
 			unlock_page(page);
 		}
 
-		pages[spd.nr_pages++] = page;
+		spd.pages[spd.nr_pages++] = page;
 		index++;
 	}
 
@@ -349,7 +382,7 @@ __generic_file_splice_read(struct file *in, loff_t *ppos,
 		 * this_len is the max we'll use from this page
 		 */
 		this_len = min_t(unsigned long, len, PAGE_CACHE_SIZE - loff);
-		page = pages[page_nr];
+		page = spd.pages[page_nr];
 
 		if (PageReadahead(page))
 			page_cache_async_readahead(mapping, &in->f_ra, in,
@@ -433,8 +466,8 @@ fill_it:
 			len = this_len;
 		}
 
-		partial[page_nr].offset = loff;
-		partial[page_nr].len = this_len;
+		spd.partial[page_nr].offset = loff;
+		spd.partial[page_nr].len = this_len;
 		len -= this_len;
 		loff = 0;
 		spd.nr_pages++;
@@ -446,12 +479,13 @@ fill_it:
 	 * we got, 'nr_pages' is how many pages are in the map.
 	 */
 	while (page_nr < nr_pages)
-		page_cache_release(pages[page_nr++]);
+		page_cache_release(spd.pages[page_nr++]);
 	in->f_ra.prev_index = index;
 
 	if (spd.nr_pages)
-		return splice_to_pipe(pipe, &spd);
+		error = splice_to_pipe(pipe, &spd);
 
+	splice_shrink_spd(pipe, &spd);
 	return error;
 }
 
@@ -708,7 +742,7 @@ ssize_t __splice_from_pipe(struct pipe_inode_info *pipe, struct splice_desc *sd,
 			if (!buf->len) {
 				buf->ops = NULL;
 				ops->release(pipe, buf);
-				pipe->curbuf = (pipe->curbuf + 1) & (PIPE_BUFFERS - 1);
+				pipe->curbuf = (pipe->curbuf + 1) & (pipe->buffers - 1);
 				pipe->nrbufs--;
 				if (pipe->inode)
 					do_wakeup = 1;
@@ -1091,7 +1125,7 @@ out_release:
 	 * If we did an incomplete transfer we must release
 	 * the pipe buffers in question:
 	 */
-	for (i = 0; i < PIPE_BUFFERS; i++) {
+	for (i = 0; i < pipe->buffers; i++) {
 		struct pipe_buffer *buf = pipe->bufs + i;
 
 		if (buf->ops) {
@@ -1232,7 +1266,8 @@ static long do_splice(struct file *in, loff_t __user *off_in,
  */
 static int get_iovec_page_array(const struct iovec __user *iov,
 				unsigned int nr_vecs, struct page **pages,
-				struct partial_page *partial, int aligned)
+				struct partial_page *partial, int aligned,
+				unsigned int pipe_buffers)
 {
 	int buffers = 0, error = 0;
 
@@ -1282,8 +1317,8 @@ static int get_iovec_page_array(const struct iovec __user *iov,
 			break;
 
 		npages = (off + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
-		if (npages > PIPE_BUFFERS - buffers)
-			npages = PIPE_BUFFERS - buffers;
+		if (npages > pipe_buffers - buffers)
+			npages = pipe_buffers - buffers;
 
 		error = get_user_pages(current, current->mm,
 				       (unsigned long) base, npages, 0, 0,
@@ -1319,7 +1354,7 @@ static int get_iovec_page_array(const struct iovec __user *iov,
 		 * or if we mapped the max number of pages that we have
 		 * room for.
 		 */
-		if (error < npages || buffers == PIPE_BUFFERS)
+		if (error < npages || buffers == pipe_buffers)
 			break;
 
 		nr_vecs--;
@@ -1461,25 +1496,33 @@ static long vmsplice_to_pipe(struct file *file, const struct iovec __user *iov,
 			     unsigned long nr_segs, unsigned int flags)
 {
 	struct pipe_inode_info *pipe;
-	struct page *pages[PIPE_BUFFERS];
-	struct partial_page partial[PIPE_BUFFERS];
+	struct page *pages[PIPE_DEF_BUFFERS];
+	struct partial_page partial[PIPE_DEF_BUFFERS];
 	struct splice_pipe_desc spd = {
 		.pages = pages,
 		.partial = partial,
 		.flags = flags,
 		.ops = &user_page_pipe_buf_ops,
 	};
+	long ret;
 
 	pipe = pipe_info(file->f_path.dentry->d_inode);
 	if (!pipe)
 		return -EBADF;
 
-	spd.nr_pages = get_iovec_page_array(iov, nr_segs, pages, partial,
-					    flags & SPLICE_F_GIFT);
+	if (splice_grow_spd(pipe, &spd))
+		return -ENOMEM;
+
+	spd.nr_pages = get_iovec_page_array(iov, nr_segs, spd.pages,
+					    spd.partial, flags & SPLICE_F_GIFT,
+					    pipe->buffers);
 	if (spd.nr_pages <= 0)
-		return spd.nr_pages;
+		ret = spd.nr_pages;
+	else
+		ret = splice_to_pipe(pipe, &spd);
 
-	return splice_to_pipe(pipe, &spd);
+	splice_shrink_spd(pipe, &spd);
+	return ret;
 }
 
 /*
@@ -1605,13 +1648,13 @@ static int link_opipe_prep(struct pipe_inode_info *pipe, unsigned int flags)
 	 * Check ->nrbufs without the inode lock first. This function
 	 * is speculative anyways, so missing one is ok.
 	 */
-	if (pipe->nrbufs < PIPE_BUFFERS)
+	if (pipe->nrbufs < pipe->buffers)
 		return 0;
 
 	ret = 0;
 	mutex_lock(&pipe->inode->i_mutex);
 
-	while (pipe->nrbufs >= PIPE_BUFFERS) {
+	while (pipe->nrbufs >= pipe->buffers) {
 		if (!pipe->readers) {
 			send_sig(SIGPIPE, current, 0);
 			ret = -EPIPE;
@@ -1663,11 +1706,11 @@ static int link_pipe(struct pipe_inode_info *ipipe,
 		 * If we have iterated all input buffers or ran out of
 		 * output room, break.
 		 */
-		if (i >= ipipe->nrbufs || opipe->nrbufs >= PIPE_BUFFERS)
+		if (i >= ipipe->nrbufs || opipe->nrbufs >= opipe->buffers)
 			break;
 
-		ibuf = ipipe->bufs + ((ipipe->curbuf + i) & (PIPE_BUFFERS - 1));
-		nbuf = (opipe->curbuf + opipe->nrbufs) & (PIPE_BUFFERS - 1);
+		ibuf = ipipe->bufs + ((ipipe->curbuf + i) & (ipipe->buffers-1));
+		nbuf = (opipe->curbuf + opipe->nrbufs) & (opipe->buffers - 1);
 
 		/*
 		 * Get a reference to this pipe buffer,
diff --git a/include/asm-generic/fcntl.h b/include/asm-generic/fcntl.h
index b847741..1d50973 100644
--- a/include/asm-generic/fcntl.h
+++ b/include/asm-generic/fcntl.h
@@ -73,6 +73,13 @@
 #define F_SETSIG	10	/* for sockets. */
 #define F_GETSIG	11	/* for sockets. */
 #endif
+#ifndef F_SETPIPE_SZ		/* for growing pipe sizes */
+#define F_SETPIPE_SZ	12
+#endif
+#ifndef F_GETPIPE_SZ
+#define F_GETPIPE_SZ	13
+#endif
+
 
 /* for F_[GET|SET]FL */
 #define FD_CLOEXEC	1	/* actually anything with low bit set goes */
diff --git a/include/linux/pipe_fs_i.h b/include/linux/pipe_fs_i.h
index 8e41202..4765076 100644
--- a/include/linux/pipe_fs_i.h
+++ b/include/linux/pipe_fs_i.h
@@ -3,7 +3,7 @@
 
 #define PIPEFS_MAGIC 0x50495045
 
-#define PIPE_BUFFERS (16)
+#define PIPE_DEF_BUFFERS	16
 
 #define PIPE_BUF_FLAG_LRU	0x01	/* page is on the LRU */
 #define PIPE_BUF_FLAG_ATOMIC	0x02	/* was atomically mapped */
@@ -44,17 +44,17 @@ struct pipe_buffer {
  **/
 struct pipe_inode_info {
 	wait_queue_head_t wait;
-	unsigned int nrbufs, curbuf;
-	struct page *tmp_page;
+	unsigned int nrbufs, curbuf, buffers;
 	unsigned int readers;
 	unsigned int writers;
 	unsigned int waiting_writers;
 	unsigned int r_counter;
 	unsigned int w_counter;
+	struct page *tmp_page;
 	struct fasync_struct *fasync_readers;
 	struct fasync_struct *fasync_writers;
 	struct inode *inode;
-	struct pipe_buffer bufs[PIPE_BUFFERS];
+	struct pipe_buffer *bufs;
 };
 
 /*
@@ -148,4 +148,7 @@ void generic_pipe_buf_get(struct pipe_inode_info *, struct pipe_buffer *);
 int generic_pipe_buf_confirm(struct pipe_inode_info *, struct pipe_buffer *);
 int generic_pipe_buf_steal(struct pipe_inode_info *, struct pipe_buffer *);
 
+/* for F_SETPIPE_SZ and F_GETPIPE_SZ */
+long pipe_fcntl(struct file *, unsigned int, unsigned long arg);
+
 #endif
diff --git a/include/linux/splice.h b/include/linux/splice.h
index 33e447f..ebb5e60 100644
--- a/include/linux/splice.h
+++ b/include/linux/splice.h
@@ -70,4 +70,11 @@ extern ssize_t splice_to_pipe(struct pipe_inode_info *,
 extern ssize_t splice_direct_to_actor(struct file *, struct splice_desc *,
 				      splice_direct_actor *);
 
+/*
+ * for dynamic pipe sizing
+ */
+extern int splice_grow_spd(struct pipe_inode_info *, struct splice_pipe_desc *);
+extern void splice_shrink_spd(struct pipe_inode_info *,
+				struct splice_pipe_desc *);
+
 #endif
diff --git a/kernel/relay.c b/kernel/relay.c
index ad85501..407e82d 100644
--- a/kernel/relay.c
+++ b/kernel/relay.c
@@ -1080,8 +1080,8 @@ static int subbuf_splice_actor(struct file *in,
 	size_t read_subbuf = read_start / subbuf_size;
 	size_t padding = rbuf->padding[read_subbuf];
 	size_t nonpad_end = read_subbuf * subbuf_size + subbuf_size - padding;
-	struct page *pages[PIPE_BUFFERS];
-	struct partial_page partial[PIPE_BUFFERS];
+	struct page *pages[PIPE_DEF_BUFFERS];
+	struct partial_page partial[PIPE_DEF_BUFFERS];
 	struct splice_pipe_desc spd = {
 		.pages = pages,
 		.nr_pages = 0,
@@ -1092,6 +1092,8 @@ static int subbuf_splice_actor(struct file *in,
 
 	if (rbuf->subbufs_produced == rbuf->subbufs_consumed)
 		return 0;
+	if (splice_grow_spd(pipe, &spd))
+		return -ENOMEM;
 
 	/*
 	 * Adjust read len, if longer than what is available
@@ -1135,16 +1137,19 @@ static int subbuf_splice_actor(struct file *in,
 		}
 	}
 
+	ret = 0;
 	if (!spd.nr_pages)
-		return 0;
+		goto out;
 
 	ret = *nonpad_ret = splice_to_pipe(pipe, &spd);
 	if (ret < 0 || ret < total_len)
-		return ret;
+		goto out;
 
         if (read_start + ret == nonpad_end)
                 ret += padding;
 
+out:
+	splice_shrink_spd(pipe, &spd);
         return ret;
 }
 

-- 
Jens Axboe

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