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SubjectRe: [PATCH 09/15] mm/hmm/devmem: device memory hotplug using ZONE_DEVICE v6
I haven't seen a newer version posted but the same comment applies on
your hmm-v25-4.9 git version from
git://people.freedesktop.org/~glisse/linux

On Wed 28-06-17 14:00:41, Jérôme Glisse wrote:
> This introduce a simple struct and associated helpers for device driver
> to use when hotpluging un-addressable device memory as ZONE_DEVICE. It
> will find a unuse physical address range and trigger memory hotplug for
> it which allocates and initialize struct page for the device memory.

Please document the hotplug semantic some more please (who is in charge,
what is the lifetime, userspace API to add/remove this memory if any
etc...).

I can see you call add_pages. Please document why arch_add_memory (like
devm_memremap_pages) is not used. You also never seem to online the
range which is in line with nvdim usage and it is OK. But then I fail to
understand why you need

[...]
> + mem_hotplug_begin();
> + ret = add_pages(nid, align_start >> PAGE_SHIFT,
> + align_size >> PAGE_SHIFT, false);
> + if (ret) {
> + mem_hotplug_done();
> + goto error_add_memory;
> + }
> + move_pfn_range_to_zone(&NODE_DATA(nid)->node_zones[ZONE_DEVICE],
> + align_start >> PAGE_SHIFT,
> + align_size >> PAGE_SHIFT);
> + mem_hotplug_done();
> +
> + for (pfn = devmem->pfn_first; pfn < devmem->pfn_last; pfn++) {
> + struct page *page = pfn_to_page(pfn);
> +
> + /*
> + * ZONE_DEVICE pages union ->lru with a ->pgmap back
> + * pointer. It is a bug if a ZONE_DEVICE page is ever
> + * freed or placed on a driver-private list. Therefore,
> + * seed the storage with LIST_POISON* values.
> + */
> + list_del(&page->lru);

this? The page is not on any list yet - it hasn't been added to the page
allocator.

> + page->pgmap = &devmem->pagemap;
> + }
> + return 0;
--
Michal Hocko
SUSE Labs

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