Messages in this thread | | | Date | Wed, 19 Aug 2020 14:54:25 +0200 | From | Michal Hocko <> | Subject | Re: [PATCH v1 02/11] mm/memory_hotplug: enforce section granularity when onlining/offlining |
| |
On Wed 19-08-20 14:43:28, David Hildenbrand wrote: > On 19.08.20 14:37, Michal Hocko wrote: > > On Wed 19-08-20 12:11:48, David Hildenbrand wrote: > >> Already two people (including me) tried to offline subsections, because > >> the function looks like it can deal with it. But we really can only > >> online/offline full sections (e.g., we can only mark full sections > >> online/offline via SECTION_IS_ONLINE). > >> > >> Add a simple safety net that to document the restriction now. Current users > >> (core and powernv/memtrace) respect these restrictions. > > > > I do agree with the warning because it clarifies our expectations > > indeed. Se below for more questions. > > > >> Cc: Andrew Morton <akpm@linux-foundation.org> > >> Cc: Michal Hocko <mhocko@suse.com> > >> Cc: Wei Yang <richard.weiyang@linux.alibaba.com> > >> Cc: Baoquan He <bhe@redhat.com> > >> Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com> > >> Cc: Oscar Salvador <osalvador@suse.de> > >> Signed-off-by: David Hildenbrand <david@redhat.com> > >> --- > >> mm/memory_hotplug.c | 10 ++++++++++ > >> 1 file changed, 10 insertions(+) > >> > >> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > >> index c781d386d87f9..6856702af68d9 100644 > >> --- a/mm/memory_hotplug.c > >> +++ b/mm/memory_hotplug.c > >> @@ -801,6 +801,11 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, > >> int ret; > >> struct memory_notify arg; > >> > >> + /* We can only online full sections (e.g., SECTION_IS_ONLINE) */ > >> + if (WARN_ON_ONCE(!nr_pages || > >> + !IS_ALIGNED(pfn | nr_pages, PAGES_PER_SECTION))) > >> + return -EINVAL; > > > > This looks looks unnecessarily cryptic to me. Do you want to catch full > > section operation that doesn't start at the usual section boundary? If > > yes the above doesn't work work unless I am missing something. > > > > Why don't you simply WARN_ON_ONCE(nr_pages % PAGES_PER_SECTION). > > !nr_pages doesn't sound like something interesting to care about or why > > do we care? > > > > Also the start pfn has to be section aligned, so we always cover fully > aligned sections (e.g., not two partial ones).
OK, I've misread your intention. I thought that we check for the start pfn prior to this warning but we only do that after.
Acked-by: Michal Hocko <mhocko@suse.com> -- Michal Hocko SUSE Labs
| |