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Message-ID: <b915143d-a8df-ddfc-94a8-7578fdd5f7bc@redhat.com>
Date: Tue, 6 Apr 2021 17:32:43 +0200
From: David Hildenbrand <david@...hat.com>
To: Oscar Salvador <osalvador@...e.de>,
Andrew Morton <akpm@...ux-foundation.org>
Cc: Michal Hocko <mhocko@...nel.org>,
Anshuman Khandual <anshuman.khandual@....com>,
Pavel Tatashin <pasha.tatashin@...een.com>,
Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 2/8] mm,memory_hotplug: Relax fully spanned sections
check
On 06.04.21 13:11, Oscar Salvador wrote:
> When using self-hosted vmemmap pages, the number of pages passed to
> {online,offline}_pages might not fully span sections, but they always
> fully span pageblocks.
> Relax the check account for that case.
>
> Signed-off-by: Oscar Salvador <osalvador@...e.de>
> ---
> mm/memory_hotplug.c | 16 ++++++++++++----
> 1 file changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 0cdbbfbc5757..5fe3e3942b19 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -838,9 +838,13 @@ 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) */
> + /* We can only offline full sections (e.g., SECTION_IS_ONLINE).
> + * However, when using e.g: memmap_on_memory, some pages are initialized
> + * prior to calling in here. The remaining amount of pages must be
> + * pageblock aligned.
> + */
> if (WARN_ON_ONCE(!nr_pages ||
> - !IS_ALIGNED(pfn | nr_pages, PAGES_PER_SECTION)))
> + !IS_ALIGNED(pfn | nr_pages, pageblock_nr_pages)))
> return -EINVAL;
>
> mem_hotplug_begin();
> @@ -1573,9 +1577,13 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages)
> int ret, node;
> char *reason;
>
> - /* We can only offline full sections (e.g., SECTION_IS_ONLINE) */
> + /* We can only offline full sections (e.g., SECTION_IS_ONLINE).
> + * However, when using e.g: memmap_on_memory, some pages are initialized
> + * prior to calling in here. The remaining amount of pages must be
> + * pageblock aligned.
> + */
> if (WARN_ON_ONCE(!nr_pages ||
> - !IS_ALIGNED(start_pfn | nr_pages, PAGES_PER_SECTION)))
> + !IS_ALIGNED(start_pfn | nr_pages, pageblock_nr_pages)))
> return -EINVAL;
>
> mem_hotplug_begin();
>
I'd only relax start_pfn. That way the function is pretty much
impossible to abuse for sub-section onlining/offlining.
if (WARN_ON_ONCE(!nr_pages ||
!IS_ALIGNED(start_pfn, pageblock_nr_pages))
!IS_ALIGNED(start_pfn + nr_pages, PAGES_PER_SECTION)))
--
Thanks,
David / dhildenb
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