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SubjectRe: [RFC PATCH 2/3] mm/memory_hotplug: Create __shrink_pages and move it to offline_pages
On Wed, Aug 08, 2018 at 03:42:33PM +0200, Oscar Salvador wrote:
> On Wed, Aug 08, 2018 at 10:08:41AM +0200, David Hildenbrand wrote:
> > Then it is maybe time to cleary distinguish both types of memory, as
> > they are fundamentally different when it comes to online/offline behavior.
> >
> > Ordinary ram:
> > add_memory ...
> > online_pages ...
> > offline_pages
> > remove_memory
> >
> > Device memory
> > add_device_memory ...
> > remove_device_memory
> >
> > So adding/removing from the zone and stuff can be handled there.
>
> Uhm, I have been thinking about this.
> Maybe we could do something like (completely untested):
>
>
> == memory_hotplug code ==
>
> int add_device_memory(int nid, unsigned long start, unsigned long size,
> struct vmem_altmap *altmap, bool mapping)
> {
> int ret;
> unsigned long start_pfn = PHYS_PFN(start);
> unsigned long nr_pages = size >> PAGE_SHIFT;
>
> mem_hotplug_begin();
> if (mapping)
> ret = arch_add_memory(nid, start, size, altmap, false)
> else
> ret = add_pages(nid, start_pfn, nr_pages, altmap, false):
>
> if (!ret) {
> pgdata_t *pgdata = NODE_DATA(nid);
> struct zone *zone = pgdata->node_zones[ZONE_DEVICE];
>
> online_mem_sections(start_pfn, start_pfn + nr_pages);
> move_pfn_range_to_zone(zone, start_pfn, nr_pages, altmap);
> }
> mem_hotplug_done();
>
> return ret;
> }
>
> int del_device_memory(int nid, unsigned long start, unsigned long size,
> struct vmem_altmap *altmap, bool mapping)
> {
> int ret;
> unsigned long start_pfn = PHYS_PFN(start);
> unsigned long nr_pages = size >> PAGE_SHIFT;
> pgdata_t *pgdata = NODE_DATA(nid);
> struct zone *zone = pgdata->node_zones[ZONE_DEVICE];
>
> mem_hotplug_begin();
>
> offline_mem_sections(start_pfn, start_pfn + nr_pages);
> __shrink_pages(zone, start_pfn, start_pfn + nr_pages, nr_pages);
>
> if (mapping)
> ret = arch_remove_memory(nid, start, size, altmap)
> else
> ret = __remove_pages(nid, start_pfn, nr_pages, altmap)
>
> mem_hotplug_done();
>
> return ret;
> }
>
> ===
>
> And then, HMM/devm code could use it.
>
> For example:
>
> hmm_devmem_pages_create():
>
> ...
> ...
> if (devmem->pagemap.type == MEMORY_DEVICE_PUBLIC)
> linear_mapping = true;
> else
> linear_mapping = false;
>
> ret = add_device_memory(nid, align_start, align_size, NULL, linear_mapping);
> if (ret)
> goto error_add_memory;
> ...
> ...
>
>
> hmm_devmem_release:
>
> ...
> ...
> if (resource->desc == IORES_DESC_DEVICE_PRIVATE_MEMORY)
> mapping = false;
> else
> mapping = true;
>
> del_device_memory(nid, start_pfn << PAGE_SHIFT, npages << PAGE_SHIFT,
> NULL,
> mapping);
> ...
> ...
>
>
> In this way, we do not need to play tricks in HMM/devm code, we just need to
> call those functions when adding/removing memory.

Note that Dan did post patches that already go in that direction (unifying
code between devm and HMM). I think they are in Andrew queue, looks for

mm: Rework hmm to use devm_memremap_pages and other fixes

>
> We would still have to figure out a way to go for the release_mem_region_adjustable() stuff though.

Yes.

Cheers,
Jérôme

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