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SubjectRe: [RFC PATCH 2/3] mm/memory_hotplug: Create __shrink_pages and move it to offline_pages
On Tue, Aug 07, 2018 at 04:54:57PM +0200, David Hildenbrand wrote:
> On 07.08.2018 15:52, Jerome Glisse wrote:
> > On Tue, Aug 07, 2018 at 03:37:56PM +0200, osalvador@techadventures.net wrote:
> >> From: Oscar Salvador <osalvador@suse.de>
> >
> > [...]
> >
> >> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> >> index 9bd629944c91..e33555651e46 100644
> >> --- a/mm/memory_hotplug.c
> >> +++ b/mm/memory_hotplug.c
> >
> > [...]
> >
> >> /**
> >> * __remove_pages() - remove sections of pages from a zone
> >> - * @zone: zone from which pages need to be removed
> >> + * @nid: node which pages belong to
> >> * @phys_start_pfn: starting pageframe (must be aligned to start of a section)
> >> * @nr_pages: number of pages to remove (must be multiple of section size)
> >> * @altmap: alternative device page map or %NULL if default memmap is used
> >> @@ -548,7 +557,7 @@ static int __remove_section(struct zone *zone, struct mem_section *ms,
> >> * sure that pages are marked reserved and zones are adjust properly by
> >> * calling offline_pages().
> >> */
> >> -int __remove_pages(struct zone *zone, unsigned long phys_start_pfn,
> >> +int __remove_pages(int nid, unsigned long phys_start_pfn,
> >> unsigned long nr_pages, struct vmem_altmap *altmap)
> >> {
> >> unsigned long i;
> >> @@ -556,10 +565,9 @@ int __remove_pages(struct zone *zone, unsigned long phys_start_pfn,
> >> int sections_to_remove, ret = 0;
> >>
> >> /* In the ZONE_DEVICE case device driver owns the memory region */
> >> - if (is_dev_zone(zone)) {
> >> - if (altmap)
> >> - map_offset = vmem_altmap_offset(altmap);
> >> - } else {
> >> + if (altmap)
> >> + map_offset = vmem_altmap_offset(altmap);
> >> + else {
> >
> > This will break ZONE_DEVICE at least for HMM. While i think that
> > altmap -> ZONE_DEVICE (ie altmap imply ZONE_DEVICE) the reverse
> > is not true ie ZONE_DEVICE does not necessarily imply altmap. So
> > with the above changes you change the expected behavior. You do
> > need the zone to know if it is a ZONE_DEVICE. You could also lookup
> > one of the struct page but my understanding is that this is what
> > you want to avoid in the first place.
>
> I wonder if we could instead forward from the callers whether we are
> dealing with ZONE_DEVICE memory (is_device ...), at least that seems
> feasible in hmm code. Not having looked at details yet.
>

Yes i believe this is doable, this add one more argument, to me it
looked like passing down the zone was good idea, i think with the
struct zone you can even remove the altmap argument.

Is there a reason why you do not want to pass down the struct zone ?

Cheers,
Jérôme

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