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Message-ID: <20250227180407.111787-1-mjguzik@gmail.com>
Date: Thu, 27 Feb 2025 19:04:07 +0100
From: Mateusz Guzik <mjguzik@...il.com>
To: brauner@...nel.org
Cc: viro@...iv.linux.org.uk,
jack@...e.cz,
oleg@...hat.com,
linux-kernel@...r.kernel.org,
linux-fsdevel@...r.kernel.org,
Mateusz Guzik <mjguzik@...il.com>
Subject: [PATCH] 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 -j 20 kernel
build.
Signed-off-by: Mateusz Guzik <mjguzik@...il.com>
---
fs/pipe.c | 67 +++++++++++++++++++++++++++------------
include/linux/pipe_fs_i.h | 2 +-
2 files changed, 48 insertions(+), 21 deletions(-)
diff --git a/fs/pipe.c b/fs/pipe.c
index 19a7948ab234..2508d14e8812 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -112,20 +112,47 @@ void pipe_double_lock(struct pipe_inode_info *pipe1,
pipe_lock(pipe2);
}
+static struct page *anon_pipe_get_page(struct pipe_inode_info *pipe)
+{
+ struct page *page;
+
+ if (pipe->tmp_page[0]) {
+ page = pipe->tmp_page[0];
+ pipe->tmp_page[0] = NULL;
+ } else if (pipe->tmp_page[1]) {
+ page = pipe->tmp_page[1];
+ pipe->tmp_page[1] = NULL;
+ } else {
+ page = alloc_page(GFP_HIGHUSER | __GFP_ACCOUNT);
+ }
+
+ return page;
+}
+
+static void anon_pipe_put_page(struct pipe_inode_info *pipe,
+ struct page *page)
+{
+ if (page_count(page) == 1) {
+ if (!pipe->tmp_page[0]) {
+ pipe->tmp_page[0] = page;
+ return;
+ }
+
+ if (!pipe->tmp_page[1]) {
+ pipe->tmp_page[1] = 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 +520,25 @@ 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);
- if (unlikely(!page)) {
- ret = ret ? : -ENOMEM;
- break;
- }
- pipe->tmp_page = page;
+ page = anon_pipe_get_page(pipe);
+ if (unlikely(!page)) {
+ if (!ret)
+ ret = -ENOMEM;
+ break;
}
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;
@@ -847,8 +872,10 @@ 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);
+ if (pipe->tmp_page[0])
+ __free_page(pipe->tmp_page[0]);
+ if (pipe->tmp_page[1])
+ __free_page(pipe->tmp_page[1]);
kfree(pipe->bufs);
kfree(pipe);
}
diff --git a/include/linux/pipe_fs_i.h b/include/linux/pipe_fs_i.h
index 8ff23bf5a819..eb7994a1ff93 100644
--- a/include/linux/pipe_fs_i.h
+++ b/include/linux/pipe_fs_i.h
@@ -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;
--
2.43.0
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