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Subject[PATCH v2 7/8] pipe: make account_pipe_buffers() return a value, and use it
Date
This is an optional patch, to provide a small performance
improvement. Alter account_pipe_buffers() so that it returns the
new value in user->pipe_bufs. This means that we can refactor
too_many_pipe_buffers_soft() and too_many_pipe_buffers_hard() to
avoid the costs of repeated use of atomic_long_read() to get the
value user->pipe_bufs.

Cc: Willy Tarreau <w@1wt.eu>
Cc: Vegard Nossum <vegard.nossum@oracle.com>
Cc: socketpair@gmail.com
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Jens Axboe <axboe@fb.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-api@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
---
fs/pipe.c | 36 ++++++++++++++++++------------------
1 file changed, 18 insertions(+), 18 deletions(-)

diff --git a/fs/pipe.c b/fs/pipe.c
index 41a580a..741560b 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -604,22 +604,20 @@ pipe_fasync(int fd, struct file *filp, int on)
return retval;
}

-static void account_pipe_buffers(struct user_struct *user,
+static unsigned long account_pipe_buffers(struct user_struct *user,
unsigned long old, unsigned long new)
{
- atomic_long_add(new - old, &user->pipe_bufs);
+ return atomic_long_add_return(new - old, &user->pipe_bufs);
}

-static bool too_many_pipe_buffers_soft(struct user_struct *user)
+static bool too_many_pipe_buffers_soft(unsigned long user_bufs)
{
- return pipe_user_pages_soft &&
- atomic_long_read(&user->pipe_bufs) >= pipe_user_pages_soft;
+ return pipe_user_pages_soft && user_bufs >= pipe_user_pages_soft;
}

-static bool too_many_pipe_buffers_hard(struct user_struct *user)
+static bool too_many_pipe_buffers_hard(unsigned long user_bufs)
{
- return pipe_user_pages_hard &&
- atomic_long_read(&user->pipe_bufs) >= pipe_user_pages_hard;
+ return pipe_user_pages_hard && user_bufs >= pipe_user_pages_hard;
}

struct pipe_inode_info *alloc_pipe_info(void)
@@ -627,19 +625,20 @@ struct pipe_inode_info *alloc_pipe_info(void)
struct pipe_inode_info *pipe;
unsigned long pipe_bufs = PIPE_DEF_BUFFERS;
struct user_struct *user = get_current_user();
+ unsigned long user_bufs;

pipe = kzalloc(sizeof(struct pipe_inode_info), GFP_KERNEL_ACCOUNT);
if (pipe == NULL)
goto out_free_uid;

- account_pipe_buffers(user, 0, pipe_bufs);
+ user_bufs = account_pipe_buffers(user, 0, pipe_bufs);

- if (too_many_pipe_buffers_soft(user)) {
- account_pipe_buffers(user, pipe_bufs, 1);
+ if (too_many_pipe_buffers_soft(user_bufs)) {
+ user_bufs = account_pipe_buffers(user, pipe_bufs, 1);
pipe_bufs = 1;
}

- if (too_many_pipe_buffers_hard(user))
+ if (too_many_pipe_buffers_hard(user_bufs))
goto out_revert_acct;

pipe->bufs = kcalloc(pipe_bufs, sizeof(struct pipe_buffer),
@@ -655,7 +654,7 @@ struct pipe_inode_info *alloc_pipe_info(void)
}

out_revert_acct:
- account_pipe_buffers(user, pipe_bufs, 0);
+ (void) account_pipe_buffers(user, pipe_bufs, 0);
kfree(pipe);
out_free_uid:
free_uid(user);
@@ -666,7 +665,7 @@ void free_pipe_info(struct pipe_inode_info *pipe)
{
int i;

- account_pipe_buffers(pipe->user, pipe->buffers, 0);
+ (void) account_pipe_buffers(pipe->user, pipe->buffers, 0);
free_uid(pipe->user);
for (i = 0; i < pipe->buffers; i++) {
struct pipe_buffer *buf = pipe->bufs + i;
@@ -1037,6 +1036,7 @@ static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg)
{
struct pipe_buffer *bufs;
unsigned int size, nr_pages;
+ unsigned long user_bufs;
long ret = 0;

size = round_pipe_size(arg);
@@ -1056,11 +1056,11 @@ static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg)
size > pipe_max_size && !capable(CAP_SYS_RESOURCE))
return -EPERM;

- account_pipe_buffers(pipe->user, pipe->buffers, nr_pages);
+ user_bufs = account_pipe_buffers(pipe->user, pipe->buffers, nr_pages);

if (nr_pages > pipe->buffers &&
- (too_many_pipe_buffers_hard(pipe->user) ||
- too_many_pipe_buffers_soft(pipe->user)) &&
+ (too_many_pipe_buffers_hard(user_bufs) ||
+ too_many_pipe_buffers_soft(user_bufs)) &&
!capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN)) {
ret = -EPERM;
goto out_revert_acct;
@@ -1112,7 +1112,7 @@ static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg)
return nr_pages * PAGE_SIZE;

out_revert_acct:
- account_pipe_buffers(pipe->user, nr_pages, pipe->buffers);
+ (void) account_pipe_buffers(pipe->user, nr_pages, pipe->buffers);
return ret;
}

--
2.5.5
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