From: David Hildenbrand <david@redhat.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Arun KS <arunks@codeaurora.org>,
Oscar Salvador <osalvador@suse.de>,
Michal Hocko <mhocko@suse.com>,
Pavel Tatashin <pasha.tatashin@soleen.com>,
Dan Williams <dan.j.williams@intel.com>
Subject: Re: [PATCH v2 4/5] mm/memory_hotplug: Make sure the pfn is aligned to the order when onlining
Date: Wed, 14 Aug 2019 23:47:24 +0200 [thread overview]
Message-ID: <784cba14-e0ad-cfea-8ffc-bfbf855ceb10@redhat.com> (raw)
In-Reply-To: <20190814135608.a449ca5a75cd700e077a8d23@linux-foundation.org>
On 14.08.19 22:56, Andrew Morton wrote:
> On Wed, 14 Aug 2019 17:41:08 +0200 David Hildenbrand <david@redhat.com> wrote:
>
>> Commit a9cd410a3d29 ("mm/page_alloc.c: memory hotplug: free pages as higher
>> order") assumed that any PFN we get via memory resources is aligned to
>> to MAX_ORDER - 1, I am not convinced that is always true. Let's play safe,
>> check the alignment and fallback to single pages.
>>
>> ...
>>
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -646,6 +646,9 @@ static int online_pages_range(unsigned long start_pfn, unsigned long nr_pages,
>> */
>> for (pfn = start_pfn; pfn < end_pfn; pfn += 1ul << order) {
>> order = min(MAX_ORDER - 1, get_order(PFN_PHYS(end_pfn - pfn)));
>> + /* __free_pages_core() wants pfns to be aligned to the order */
>> + if (unlikely(!IS_ALIGNED(pfn, 1ul << order)))
>> + order = 0;
>> (*online_page_callback)(pfn_to_page(pfn), order);
>> }
>
> We aren't sure if this occurs, but if it does, we silently handle it.
>
> It seems a reasonable defensive thing to do, but should we add a
> WARN_ON_ONCE() so that we get to find out about it? If we get such a
> report then we can remove the WARN_ON_ONCE() and add an illuminating
> comment.
>
>
Makes sense, do you want to add the WARN_ON_ONCE() or shall I resend?
I was recently thinking about limiting offlining to memory blocks
without holes - then also onlining would only apply to memory blocks
without holes and we could simplify both paths (single zone/node, no
holes) - including this check, we would always have memory block size
alignments. But I am not sure yet if there is a valid use case for
offlining/re-online boot memory with holes.
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2019-08-14 21:47 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-14 15:41 [PATCH v2 0/5] mm/memory_hotplug: online_pages() cleanups David Hildenbrand
2019-08-14 15:41 ` [PATCH v2 1/5] resource: Use PFN_UP / PFN_DOWN in walk_system_ram_range() David Hildenbrand
2019-08-14 16:15 ` Wei Yang
2019-08-14 15:41 ` [PATCH v2 2/5] mm/memory_hotplug: Drop PageReserved() check in online_pages_range() David Hildenbrand
2019-08-14 16:04 ` Michal Hocko
2019-08-14 15:41 ` [PATCH v2 3/5] mm/memory_hotplug: Simplify online_pages_range() David Hildenbrand
2019-08-14 16:07 ` Michal Hocko
2019-08-14 15:41 ` [PATCH v2 4/5] mm/memory_hotplug: Make sure the pfn is aligned to the order when onlining David Hildenbrand
2019-08-14 16:09 ` David Hildenbrand
2019-08-14 18:32 ` Michal Hocko
2019-08-14 19:04 ` David Hildenbrand
2019-08-14 20:56 ` Andrew Morton
2019-08-14 21:47 ` David Hildenbrand [this message]
2019-08-14 22:10 ` Andrew Morton
2019-08-14 15:41 ` [PATCH v2 5/5] mm/memory_hotplug: online_pages cannot be 0 in online_pages() David Hildenbrand
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