From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vegard Nossum Subject: Re: [PATCH 7/8] pipe: make account_pipe_buffers() return a value, and use it Date: Fri, 19 Aug 2016 11:36:03 +0200 Message-ID: <57B6D303.2060301@oracle.com> References: <67ce15aa-cf43-0c89-d079-2d966177c56d@gmail.com> <676aa52b-c4fc-3bf1-8051-39deca8bf0ab@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <676aa52b-c4fc-3bf1-8051-39deca8bf0ab-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: "Michael Kerrisk (man-pages)" , Andrew Morton Cc: Willy Tarreau , socketpair-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, Tetsuo Handa , Jens Axboe , Al Viro , linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-api@vger.kernel.org On 08/19/2016 07:25 AM, Michael Kerrisk (man-pages) wrote: > 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. [...] > @@ -627,17 +625,18 @@ 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 num_bufs; Maybe user_bufs would be more descriptive since num_bufs is a bit ambiguous without the context. > > pipe = kzalloc(sizeof(struct pipe_inode_info), GFP_KERNEL_ACCOUNT); > if (pipe == NULL) > goto out_free_uid; > > - if (too_many_pipe_buffers_soft(user)) > + if (too_many_pipe_buffers_soft(atomic_long_read(&user->pipe_bufs))) > pipe_bufs = 1; > > - account_pipe_buffers(user, 0, pipe_bufs); > + num_bufs = account_pipe_buffers(user, 0, pipe_bufs); > > - if (too_many_pipe_buffers_hard(user)) > + if (too_many_pipe_buffers_hard(num_bufs)) > goto out_revert_acct; > > pipe->bufs = kcalloc(pipe_bufs, sizeof(struct pipe_buffer), Why not structure it like this? num_bufs = account_pipe_buffers(user, 0, pipe_bufs); if (too_many_pipe_buffers_soft(num_bufs)) { num_bufs = account_pipe_buffers(user, pipe_bufs, 1); pipe_bufs = 1; } if (too_many_pipe_buffers_hard(num_bufs)) goto out_revert_acct; Otherwise you still have the case that somebody makes it past too_many_pipe_buffers_soft() before the accounting is done. Vegard