Re: [PATCH V6 1/2] mm/page_alloc: Make alloc_gigantic_page() available for general use

From: Michal Hocko <mhocko@kernel.org>
To: David Hildenbrand <david@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
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Subject: Re: [PATCH V6 1/2] mm/page_alloc: Make alloc_gigantic_page() available for general use
Date: Tue, 15 Oct 2019 14:09:56 +0200	[thread overview]
Message-ID: <20191015120956.GF317@dhcp22.suse.cz> (raw)
In-Reply-To: <513bc2f7-8110-58f7-36c1-a04b59f11f7e@redhat.com>

On Tue 15-10-19 13:50:02, David Hildenbrand wrote:
> On 15.10.19 13:47, Michal Hocko wrote:
> > On Tue 15-10-19 13:42:03, David Hildenbrand wrote:
> > [...]
> > > > -static bool pfn_range_valid_gigantic(struct zone *z,
> > > > -			unsigned long start_pfn, unsigned long nr_pages)
> > > > -{
> > > > -	unsigned long i, end_pfn = start_pfn + nr_pages;
> > > > -	struct page *page;
> > > > -
> > > > -	for (i = start_pfn; i < end_pfn; i++) {
> > > > -		if (!pfn_valid(i))
> > > > -			return false;
> > > > -
> > > > -		page = pfn_to_page(i);
> > > 
> > > Am I missing something or should here really be a pfn_to_online_page() here
> > > instead of a pfn_valid() ?
> > 
> > http://lkml.kernel.org/r/20180423000943.GO17484@dhcp22.suse.cz
> > 
> 
> So we managed to add PageReserved(page) but not pfn_to_online_page(). But it
> is the right thing to do? (or am I missing something?)

Yeah, pfn_to_online_page is better. But please note that this is an
optimistic check. The real check has to be done when isolating the
pageblock because things might change in the meantime.
-- 
Michal Hocko
SUSE Labs