Unverified Commit 46af8e24 authored by Mateusz Guzik's avatar Mateusz Guzik Committed by Christian Brauner
Browse files

pipe: cache 2 pages instead of 1 



User data is kept in a circular buffer backed by pages allocated as
needed. Only having space for one spare is still prone to having to
resort to allocation / freeing.

In my testing this decreases page allocs by 60% during a kernel build.

Signed-off-by: default avatarMateusz Guzik <mjguzik@gmail.com>
Link: https://lore.kernel.org/r/20250303230409.452687-3-mjguzik@gmail.com


Signed-off-by: default avatarChristian Brauner <brauner@kernel.org>
parent a40cd584

fs/pipe.c

+40 −20
Original line number Diff line number Diff line
@@ -112,20 +112,40 @@ void pipe_double_lock(struct pipe_inode_info *pipe1, 
	pipe_lock(pipe2);

}



static struct page *anon_pipe_get_page(struct pipe_inode_info *pipe)

{

	for (int i = 0; i < ARRAY_SIZE(pipe->tmp_page); i++) {

		if (pipe->tmp_page[i]) {

			struct page *page = pipe->tmp_page[i];

			pipe->tmp_page[i] = NULL;

			return page;

		}

	}



	return alloc_page(GFP_HIGHUSER | __GFP_ACCOUNT);

}



static void anon_pipe_put_page(struct pipe_inode_info *pipe,

			       struct page *page)

{

	if (page_count(page) == 1) {

		for (int i = 0; i < ARRAY_SIZE(pipe->tmp_page); i++) {

			if (!pipe->tmp_page[i]) {

				pipe->tmp_page[i] = page;

				return;

			}

		}

	}



	put_page(page);

}



static void anon_pipe_buf_release(struct pipe_inode_info *pipe,

				  struct pipe_buffer *buf)

{

	struct page *page = buf->page;



	/*

	 * If nobody else uses this page, and we don't already have a

	 * temporary page, let's keep track of it as a one-deep

	 * allocation cache. (Otherwise just release our reference to it)

	 */

	if (page_count(page) == 1 && !pipe->tmp_page)

		pipe->tmp_page = page;

	else

		put_page(page);

	anon_pipe_put_page(pipe, page);

}



static bool anon_pipe_buf_try_steal(struct pipe_inode_info *pipe,
@@ -493,27 +513,25 @@ anon_pipe_write(struct kiocb *iocb, struct iov_iter *from) 
		if (!pipe_full(head, pipe->tail, pipe->max_usage)) {

			unsigned int mask = pipe->ring_size - 1;

			struct pipe_buffer *buf;

			struct page *page = pipe->tmp_page;

			struct page *page;

			int copied;



			if (!page) {

				page = alloc_page(GFP_HIGHUSER | __GFP_ACCOUNT);

			page = anon_pipe_get_page(pipe);

			if (unlikely(!page)) {

					ret = ret ? : -ENOMEM;

				if (!ret)

					ret = -ENOMEM;

				break;

			}

				pipe->tmp_page = page;

			}



			copied = copy_page_from_iter(page, 0, PAGE_SIZE, from);

			if (unlikely(copied < PAGE_SIZE && iov_iter_count(from))) {

				anon_pipe_put_page(pipe, page);

				if (!ret)

					ret = -EFAULT;

				break;

			}



			pipe->head = head + 1;

			pipe->tmp_page = NULL;

			/* Insert it into the buffer array */

			buf = &pipe->bufs[head & mask];

			buf->page = page;
@@ -846,8 +864,10 @@ void free_pipe_info(struct pipe_inode_info *pipe) 
	if (pipe->watch_queue)

		put_watch_queue(pipe->watch_queue);

#endif

	if (pipe->tmp_page)

		__free_page(pipe->tmp_page);

	for (i = 0; i < ARRAY_SIZE(pipe->tmp_page); i++) {

		if (pipe->tmp_page[i])

			__free_page(pipe->tmp_page[i]);

	}

	kfree(pipe->bufs);

	kfree(pipe);

}

include/linux/pipe_fs_i.h

+1 −1
Original line number Diff line number Diff line
@@ -72,7 +72,7 @@ struct pipe_inode_info { 
#ifdef CONFIG_WATCH_QUEUE

	bool note_loss;

#endif

	struct page *tmp_page;

	struct page *tmp_page[2];

	struct fasync_struct *fasync_readers;

	struct fasync_struct *fasync_writers;

	struct pipe_buffer *bufs;