pipe: make account_pipe_buffers() return a value, and use it

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.

Link: http://lkml.kernel.org/r/93e5f193-1e5e-3e1f-3a20-eae79b7e1310@gmail.com
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Reviewed-by: Vegard Nossum <vegard.nossum@oracle.com>
Cc: Willy Tarreau <w@1wt.eu>
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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/pipe.c b/fs/pipe.c
index 83a2924..5ff02c4 100644 (file)
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -601,22 +601,20 @@ 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)
@@ -624,19 +622,20 @@ 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),
@@ -652,7 +651,7 @@ 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);
@@ -663,7 +662,7 @@ 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;
@@ -1034,6 +1033,7 @@ 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);
@@ -1053,11 +1053,11 @@ 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;
@@ -1109,7 +1109,7 @@ 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;
 }