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SubjectRe: [PATCH v1 2/4] mm/memory_hotplug: Handle unaligned start and nr_pages in online_pages_blocks()
On Fri 09-08-19 14:56:59, David Hildenbrand wrote:
> Take care of nr_pages not being a power of two and start not being
> properly aligned. Essentially, what walk_system_ram_range() could provide
> to us. get_order() will round-up in case it's not a power of two.
>
> This should only apply to memory blocks that contain strange memory
> resources (especially with holes), not to ordinary DIMMs.

I would really like to see an example of such setup before making the
code hard to read. Because I am not really sure something like that
exists at all.

> Fixes: a9cd410a3d29 ("mm/page_alloc.c: memory hotplug: free pages as higher order")
> Cc: Arun KS <arunks@codeaurora.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
> mm/memory_hotplug.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 3706a137d880..2abd938c8c45 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -640,6 +640,10 @@ static int online_pages_blocks(unsigned long start, unsigned long nr_pages)
> while (start < end) {
> order = min(MAX_ORDER - 1,
> get_order(PFN_PHYS(end) - PFN_PHYS(start)));
> + /* make sure the PFN is aligned and we don't exceed the range */
> + while (!IS_ALIGNED(start, 1ul << order) ||
> + (1ul << order) > end - start)
> + order--;
> (*online_page_callback)(pfn_to_page(start), order);
>
> onlined_pages += (1UL << order);
> --
> 2.21.0

--
Michal Hocko
SUSE Labs

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