Re: [PATCH v5] add MAP_UNLOCKED mmap flag

KOSAKI Motohiro
2010-01-14T07:02:47Z

> On Thu, Jan 14, 2010 at 09:31:03AM +0900, KOSAKI Motohiro wrote:
> > > If application does mlockall(MCL_FUTURE) it is no longer possible to mmap
> > > file bigger than main memory or allocate big area of anonymous memory
> > > in a thread safe manner. Sometimes it is desirable to lock everything
> > > related to program execution into memory, but still be able to mmap
> > > big file or allocate huge amount of memory and allow OS to swap them on
> > > demand. MAP_UNLOCKED allows to do that.
> > >
> > > Signed-off-by: Gleb Natapov <gleb@redhat.com>
> > > ---
> > >
> > > I get reports that people find this useful, so resending.
> >
> > This description is still wrong. It doesn't describe why this patch is useful.
> >
> I think the text above describes the feature it adds and its use
> case quite well. Can you elaborate what is missing in your opinion,
> or suggest alternative text please?

My point is, introducing mmap new flags need strong and clearly use-case.
All patch should have good benefit/cost balance. the code can describe the cost,
but the benefit can be only explained by the patch description.

I don't think this poor description explained bit benefit rather than cost.
you should explain why this patch is useful and not just pretty toy.