Seeking consensus on BZ 16734

[Rich Felker]

On Sun, Feb 01, 2015 at 08:46:06PM -0800, Paul Pluzhnikov wrote:
> On Sun, Feb 1, 2015 at 8:09 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> 
> >> Can we just do it?
> >>
> >
> > Do we have any current performance data on this?
> 
> I am not sure what performance data you want.
> 
> The application CPU will go up (calloc has to zero out space), kernel
> CPU will go down (kernel would not have to zero out the same space).
> 
> It's clear that calloc()ing 8K is much cheaper than mmap()ing,
> especially when there are 100s of threads.

The original idea seems to be some misguided idea that read/write
should perform better with a page-aligned buffer. I can't make any
sense of this believe except in the case of the O_DIRECT silliness
Linux supports; normally IO is going to be memcpy to/from fs cache
buffers and there's no reason to expect page alignment to make that
faster.

Rich