Re: [PATCH 7/8] pipe: make account_pipe_buffers() return a value, and use it
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From: Vegard Nossum <hidden>
Date: 2016-08-19 09:36:53
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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.
[...]
quoted hunk ↗ jump to hunk
@@ -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.
quoted hunk ↗ jump to hunk
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