On Fri 20-11-15 15:33:17, David Rientjes wrote:
> On Fri, 20 Nov 2015, Michal Hocko wrote:
>
> > > > @@ -3167,24 +3166,21 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> > > >
> > > > /*
> > > > * Do not retry high order allocations unless they are __GFP_REPEAT
> > > > - * and even then do not retry endlessly unless explicitly told so
> > > > + * unless explicitly told so.
> > > > */
> > > > - pages_reclaimed += did_some_progress;
> > > > - if (order > PAGE_ALLOC_COSTLY_ORDER) {
> > > > - if (!(gfp_mask & __GFP_NOFAIL) &&
> > > > - (!(gfp_mask & __GFP_REPEAT) || pages_reclaimed >= (1<<order)))
> > > > - goto noretry;
> > > > -
> > > > - if (did_some_progress)
> > > > - goto retry;
> > > > - }
> > > > + if (order > PAGE_ALLOC_COSTLY_ORDER &&
> > > > + !(gfp_mask & (__GFP_REPEAT|__GFP_NOFAIL)))
> > > > + goto noretry;
> > >
> > > Who is allocating order > PAGE_ALLOC_COSTLY_ORDER with __GFP_REPEAT and
> > > would be affected by this change?
> >
> > E.g. hugetlb pages. I have tested this in my testing scenario 3.
> >
>
> If that's the only high-order user of __GFP_REPEAT, we might want to
> consider dropping it.
There are many others. I have tried to clean this area up quite recently
http://lkml.kernel.org/r/1446740160-29094-1-git-send-email-mhocko%40kernel.org
and managed to drop half of the current usage of __GFP_REPEAT.
> I believe the hugetlb usecase would only be
> relevant in early init (when __GFP_REPEAT shouldn't logically help) and
> when returning surplus pages due to hugetlb overcommit. Since hugetlb
> overcommit is best effort and we already know that the
> pages_reclaimed >= (1<<order) check is ridiculous for order-9 pages, I
> think you could just drop hugetlb's usage of __GFP_REPEAT and nobody would
> notice.
Even if that was the case, which I am not sure right now, I believe this
is a separate topic. We should still support __GFP_REPEAT in some form.
--
Michal Hocko
SUSE Labs
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