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From: Oscar Salvador <osalvador@suse.de>
To: Michal Hocko <mhocko@kernel.org>
Cc: n-horiguchi@ah.jp.nec.com, mike.kravetz@oracle.com,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH v2 11/16] mm,hwpoison: Rework soft offline for in-use pages
Date: Mon, 21 Oct 2019 15:48:48 +0200
Message-ID: <20191021134846.GB11330@linux> (raw)
In-Reply-To: <20191018123901.GN5017@dhcp22.suse.cz>

On Fri, Oct 18, 2019 at 02:39:01PM +0200, Michal Hocko wrote:
> 
> I am sorry but I got lost in the above description and I cannot really
> make much sense from the code either. Let me try to outline the way how
> I think about this.
> 
> Say we have a pfn to hwpoison. We have effectivelly three possibilities
> - page is poisoned already - done nothing to do
> - page is managed by the buddy allocator - excavate from there
> - page is in use
> 
> The last category is the most interesting one. There are essentially
> three classes of pages
> - freeable
> - migrateable
> - others
> 
> We cannot do really much about the last one, right? Do we mark them
> HWPoison anyway?

We can only perform actions on LRU/Movable pages or hugetlb pages.

So unless the page does not fall into those areas, we do not do anything
with them.

> Freeable should be simply marked HWPoison and freed.
> For all those migrateable, we simply do migrate and mark HWPoison.
> Now the main question is how to handle HWPoison page when it is freed
> - aka last reference is dropped. The main question is whether the last
> reference is ever dropped. If yes then the free_pages_prepare should
> never release it to the allocator (some compound destructors would have
> to special case as well, e.g. hugetlb would have to hand over to the
> allocator rather than a pool). If not then the page would be lingering
> potentially with some state bound to it (e.g. memcg charge).  So I
> suspect you want the former.

For non-hugetlb pages, we do not call put_page in the migration path,
but we do it in page_handle_poison, after the page has been flagged as
hwpoison.
Then the check in free_papes_prepare will see that the page is hwpoison
and will bail out, so the page is not released into the allocator/pcp lists.

Hugetlb pages follow a different methodology.
They are dissolved, and then we split the higher-order page and take the
page off the buddy.
The problem is that while it is easy to hold a non-hugetlb page,
doing the same for hugetlb pages is not that easy:

1) we would need to hook in enqueue_hugetlb_page so the page is not enqueued
   into hugetlb freelists
2) when trying to free a hugetlb page, we would need to do as we do for gigantic
   pages now, and that is breaking down the pages into order-0 pages and release
   them to the buddy (so the check in free_papges_prepare would skip the
   hwpoison page).
   Trying to handle a higher-order hwpoison page in free_pages_prepare is
   a bit complicated.
   
There is one thing I was unsure though.
Bailing out at the beginning of free_pages_prepare if the page is hwpoison
means that the calls to

- __memcg_kmem_uncharge
- page_cpupid_reset_last
- reset_page_owner
- ...

will not be performed.
I thought this is right because the page is not really "free", it is just unusable,
so.. it should be still charged to the memcg?

-- 
Oscar Salvador
SUSE L3


  reply index

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-17 14:21 [RFC PATCH v2 00/16] Hwpoison rework {hard,soft}-offline Oscar Salvador
2019-10-17 14:21 ` [RFC PATCH v2 01/16] mm,hwpoison: cleanup unused PageHuge() check Oscar Salvador
2019-10-18 11:48   ` Michal Hocko
2019-10-21  7:00     ` Naoya Horiguchi
2019-10-21 12:16       ` Michal Hocko
2019-11-12 12:22       ` Aneesh Kumar K.V
2019-11-13  6:02         ` Naoya Horiguchi
2019-10-17 14:21 ` [RFC PATCH v2 02/16] mm,madvise: call soft_offline_page() without MF_COUNT_INCREASED Oscar Salvador
2019-10-18 11:52   ` Michal Hocko
2019-10-21  7:02     ` Naoya Horiguchi
2019-10-21 12:20       ` Michal Hocko
2019-10-17 14:21 ` [RFC PATCH v2 03/16] mm,madvise: Refactor madvise_inject_error Oscar Salvador
2019-10-21  7:03   ` Naoya Horiguchi
2019-10-17 14:21 ` [RFC PATCH v2 04/16] mm,hwpoison-inject: don't pin for hwpoison_filter Oscar Salvador
2019-10-17 14:21 ` [RFC PATCH v2 05/16] mm,hwpoison: Un-export get_hwpoison_page and make it static Oscar Salvador
2019-10-21  7:03   ` Naoya Horiguchi
2019-10-17 14:21 ` [RFC PATCH v2 06/16] mm,hwpoison: Kill put_hwpoison_page Oscar Salvador
2019-10-21  7:04   ` Naoya Horiguchi
2019-10-17 14:21 ` [RFC PATCH v2 07/16] mm,hwpoison: remove MF_COUNT_INCREASED Oscar Salvador
2019-10-17 14:21 ` [RFC PATCH v2 08/16] mm,hwpoison: remove flag argument from soft offline functions Oscar Salvador
2019-10-17 14:21 ` [RFC PATCH v2 09/16] mm,hwpoison: Unify THP handling for hard and soft offline Oscar Salvador
2019-10-21  7:04   ` Naoya Horiguchi
2019-10-21  9:51     ` [PATCH 17/16] mm,hwpoison: introduce MF_MSG_UNSPLIT_THP Naoya Horiguchi
2019-10-22  8:00       ` Oscar Salvador
2019-10-17 14:21 ` [RFC PATCH v2 10/16] mm,hwpoison: Rework soft offline for free pages Oscar Salvador
2019-10-18 12:06   ` Michal Hocko
2019-10-21 12:58     ` Oscar Salvador
2019-10-21 15:41       ` Michal Hocko
2019-10-22  7:46         ` Oscar Salvador
2019-10-22  8:26           ` Michal Hocko
2019-10-22  8:35             ` Oscar Salvador
2019-10-22  9:22               ` Michal Hocko
2019-10-22  9:58                 ` Oscar Salvador
2019-10-22 10:24                   ` Michal Hocko
2019-10-22 10:33                     ` Oscar Salvador
2019-10-23  2:15                       ` Naoya Horiguchi
2019-10-23  2:01                   ` Naoya Horiguchi
2019-10-21  7:45   ` Naoya Horiguchi
2019-10-22  8:00     ` Oscar Salvador
2019-10-17 14:21 ` [RFC PATCH v2 11/16] mm,hwpoison: Rework soft offline for in-use pages Oscar Salvador
2019-10-18 12:39   ` Michal Hocko
2019-10-21 13:48     ` Oscar Salvador [this message]
2019-10-21 14:06       ` Michal Hocko
2019-10-22  7:56         ` Oscar Salvador
2019-10-22  8:30           ` Michal Hocko
2019-10-22  9:40             ` Oscar Salvador
2019-10-17 14:21 ` [RFC PATCH v2 12/16] mm,hwpoison: Refactor soft_offline_huge_page and __soft_offline_page Oscar Salvador
2019-10-17 14:21 ` [RFC PATCH v2 13/16] mm,hwpoison: Take pages off the buddy when hard-offlining Oscar Salvador
2019-10-17 14:21 ` [RFC PATCH v2 14/16] mm,hwpoison: Return 0 if the page is already poisoned in soft-offline Oscar Salvador
2019-10-21  9:20   ` Naoya Horiguchi
2019-10-17 14:21 ` [RFC PATCH v2 15/16] mm/hwpoison-inject: Rip off duplicated checks Oscar Salvador
2019-10-21  9:40   ` David Hildenbrand
2019-10-22  7:57     ` Oscar Salvador
2019-10-17 14:21 ` [RFC PATCH v2 16/16] mm, soft-offline: convert parameter to pfn Oscar Salvador
2019-10-18  8:15   ` David Hildenbrand
2020-06-11 16:43 ` [RFC PATCH v2 00/16] Hwpoison rework {hard,soft}-offline Dmitry Yakunin
2020-06-15  6:19   ` HORIGUCHI NAOYA(堀口 直也)

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