Re: [PATCH v2 0/4] malloc: Improve Huge Page support

[Guillaume Morin <guillaume@morinfr.org>]

On 19 Aug 13:55, Adhemerval Zanella wrote:
> On 19/08/2021 13:42, Guillaume Morin wrote:
> > Are you planning on tackling using the same tunables to allocate
> > additional heaps (in arena.c)?
> > 
> > It's a little more subtle because of the calls to mprotect() which needs
> > to be properly aligned for hugetlbfs, and probably for THP as well (to
> > avoid un-necessary page splitting).
> 
> What do you mean by additional heaps in this case?

I mean what is done in new_heap() in arena.c.

> > One additional thing to address is the case where mmap() fails with
> > MAP_HUGETLB because HP allocation fails.  Reverting to the default pages
> > will match what libhugetlbfs does (i.e just call mmap() again without
> > MAP_HUGETLB). But I see that Siddhesh and you have already been
> > discussing this case.
> 
> This is what I did in my patch, it follow the current default allocation
> path.

Yes, you are right. I misread. You've been discussing adding a tunable
to decide if that should fail or not. My 2 cents as a user: it's hard
for me to imagine that users would like malloc() to fail in this case.
Even if the admin allows surplus pages (i.e create new HPs on the fly),
this is far from guaranteed to succeed.

Guillaume.

-- 
Guillaume Morin <guillaume@morinfr.org>