Messages in this thread | | | From | Oscar Salvador <> | Subject | [PATCH 00/10] Hwpoison soft-offline rework | Date | Tue, 10 Sep 2019 12:30:06 +0200 |
| |
This patchset was based on Naoya's hwpoison rework [1], so thanks to him for the initial work.
This patchset aims to fix some issues laying in soft-offline handling, but it also takes the chance and takes some further steps to perform cleanups and some refactoring as well.
- Motivation:
A customer and I were facing an issue where poisoned pages we returned back to user-space after having offlined them properly. This was only seend under some memory stress + soft offlining pages. After some anaylsis, it became clear that the problem was that when kcompactd kicked in to migrate pages over, compaction_alloc callback was handing poisoned pages to the migrate routine. Once this page was later on fault in, __do_page_fault returned VM_FAULT_HWPOISON making the process being killed.
All this could happen because isolate_freepages_block and fast_isolate_freepages just check for the page to be PageBuddy, and since 1) poisoned pages can be part of a higher order page and 2) poisoned pages are also Page Buddy, they can sneak in easily.
I also saw some problem with swap pages, but I suspected to be the same sort of problem, so I did not follow that trace.
The full explanation can be see in [2].
- Approach:
The taken approach is to not let poisoned pages hit neither pcplists nor buddy freelists. This is achieved by:
In-use pages:
* Normal pages
1) do not release the last reference count after the invalidation/migration of the page. 2) the page is being handed to page_set_poison, which does: 2a) sets PageHWPoison flag 2b) calls put_page (only to be able to call __page_cache_release) Since poisoned pages are skipped in free_pages_prepare, this put_page is safe. 2c) Sets the refcount to 1
* Hugetlb pages
1) Hand the page to page_set_poison after migration 2) page_set_poison does: 2a) Calls dissolve_free_huge_page 2b) If ranged to be dissolved contains poisoned pages, we free the rangeas order-0 pages (as we do with gigantic hugetlb page), so free_pages_prepare will skip them accordingly. 2c) Sets the refcount to 1
Free pages:
* Normal pages:
1) Take the page off the buddy freelist 2) Set PageHWPoison flag and set refcount to 1
* Hugetlb pages
1) Try to allocate a new hugetlb page to the pool 2) Take off the pool the poisoned hugetlb
With this patchset, I no longer see the issues I faced before.
Note: I presented this as RFC to open discussion of the taken aproach. I think that furthers cleanups and refactors could be made, but I would like to get some insight of the taken approach before touching more code.
Thanks
[1] https://lore.kernel.org/linux-mm/1541746035-13408-1-git-send-email-n-horiguchi@ah.jp.nec.com/ [2] https://lore.kernel.org/linux-mm/20190826104144.GA7849@linux/T/#u
Naoya Horiguchi (5): mm,hwpoison: cleanup unused PageHuge() check mm,madvise: call soft_offline_page() without MF_COUNT_INCREASED mm,hwpoison-inject: don't pin for hwpoison_filter mm,hwpoison: remove MF_COUNT_INCREASED mm: remove flag argument from soft offline functions
Oscar Salvador (5): mm,hwpoison: Unify THP handling for hard and soft offline mm,hwpoison: Rework soft offline for in-use pages mm,hwpoison: Refactor soft_offline_huge_page and __soft_offline_page mm,hwpoison: Rework soft offline for free pages mm,hwpoison: Use hugetlb_replace_page to replace free hugetlb pages
drivers/base/memory.c | 2 +- include/linux/mm.h | 9 +- include/linux/page-flags.h | 5 - mm/hugetlb.c | 51 +++++++- mm/hwpoison-inject.c | 18 +-- mm/madvise.c | 25 ++-- mm/memory-failure.c | 319 +++++++++++++++++++++------------------------ mm/migrate.c | 11 +- mm/page_alloc.c | 62 +++++++-- 9 files changed, 267 insertions(+), 235 deletions(-)
-- 2.12.3
| |