Re: memory offline infinite loop after soft offline

From: David Hildenbrand
Date: Fri Oct 18 2019 - 07:51:17 EST

On 18.10.19 13:34, Michal Hocko wrote:
On Fri 18-10-19 13:00:45, David Hildenbrand wrote:
On 18.10.19 10:55, Michal Hocko wrote:
On Fri 18-10-19 10:38:21, David Hildenbrand wrote:
On 18.10.19 10:24, Michal Hocko wrote:
On Fri 18-10-19 10:13:36, David Hildenbrand wrote:
However, if the compound page spans multiple pageblocks

Although hugetlb pages spanning pageblocks are possible this shouldn't
matter in__test_page_isolated_in_pageblock because this function doesn't
really operate on pageblocks as the name suggests. It is simply
traversing all valid RAM ranges (see walk_system_ram_range).

As long as the hugepages don't span memory blocks/sections, you are right. I
have no experience with gigantic pages in this regard.

They can clearly span sections (1GB is larger than 128MB). Why do you
think it matters actually? walk_system_ram_range walks RAM ranges and no
allocation should span holes in RAM right?

Let's explore what I was thinking. If we can agree that any compound page is
always aligned to its size , then what I tell here is not applicable. I know
it is true for gigantic pages.

Some extreme example to clarify

[ memory block 0 (128MB) ][ memory block 1 (128MB) ]
[ compound page (128MB) ]

If you would offline memory block 1, and you detect PG_offline on the first
page of that memory block (PageHWPoison(compound_head(page))), you would
jump over the whole memory block (pfn += 1 << compound_order(page)), leaving
64MB of the memory block unchecked.

Again, if any compound page has the alignment restrictions (PFN of head
aligned to 1 << compound_order(page)), this is not possible.

If it is, however, possible, the "clean" thing would be to only jump over
the remaining part of the compound page, e.g., something like

pfn += (1 << compound_order(page)) - (page - compound_head(page)));

OK, I see what you mean now. In other words similar to eeb0efd071d82.




David / dhildenb