Re: [PATCH 17/18] mm, hugetlb: retry if we fail to allocate ahugepage with use_reserve

From: Davidlohr Bueso
Date: Tue Aug 06 2013 - 20:19:16 EST

On Mon, 2013-08-05 at 16:36 +0900, Joonsoo Kim wrote:
> > Any mapping that doesn't use the reserved pool, not just
> > MAP_NORESERVE. For example, if a process makes a MAP_PRIVATE mapping,
> > then fork()s then the mapping is instantiated in the child, that will
> > not draw from the reserved pool.
> >
> > > Should we ensure them to allocate the last hugepage?
> > > They map a region with MAP_NORESERVE, so don't assume that their requests
> > > always succeed.
> >
> > If the pages are available, people get cranky if it fails for no
> > apparent reason, MAP_NORESERVE or not. They get especially cranky if
> > it sometimes fails and sometimes doesn't due to a race condition.
> Hello,
> Hmm... Okay. I will try to implement another way to protect race condition.
> Maybe it is the best to use a table mutex :)
> Anyway, please give me a time, guys.

So another option is to take the mutex table patchset for now as it
*does* improve things a great deal, then, when ready, get rid of the
instantiation lock all together.


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