Date:   Mon, 3 Aug 2020 15:07:09 -0400
From:   Qian Cai <cai@....pw>
To:     nao.horiguchi@...il.com
Cc:     linux-mm@...ck.org, mhocko@...nel.org, akpm@...ux-foundation.org,
        mike.kravetz@...cle.com, osalvador@...e.de, tony.luck@...el.com,
        david@...hat.com, aneesh.kumar@...ux.vnet.ibm.com,
        zeil@...dex-team.ru, naoya.horiguchi@....com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 00/16] HWPOISON: soft offline rework

On Fri, Jul 31, 2020 at 12:20:56PM +0000, nao.horiguchi@...il.com wrote:
> This patchset is the latest version of soft offline rework patchset
> targetted for v5.9.
> 
> Main focus of this series is to stabilize soft offline.  Historically soft
> offlined pages have suffered from racy conditions because PageHWPoison is
> used to a little too aggressively, which (directly or indirectly) invades
> other mm code which cares little about hwpoison.  This results in unexpected
> behavior or kernel panic, which is very far from soft offline's "do not
> disturb userspace or other kernel component" policy.
> 
> Main point of this change set is to contain target page "via buddy allocator",
> where we first free the target page as we do for normal pages, and remove
> from buddy only when we confirm that it reaches free list. There is surely
> race window of page allocation, but that's fine because someone really want
> that page and the page is still working, so soft offline can happily give up.
> 
> v4 from Oscar tries to handle the race around reallocation, but that part
> seems still work in progress, so I decide to separate it for changes into
> v5.9.  Thank you for your contribution, Oscar.
> 
> The issue reported by Qian Cai is fixed by patch 16/16.
> 
> This patchset is based on v5.8-rc7-mmotm-2020-07-27-18-18, but I applied
> this series after reverting previous version.
> Maybe https://github.com/Naoya-Horiguchi/linux/commits/soft-offline-rework.v5
> shows what I did more precisely.
> 
> Any other comment/suggestion/help would be appreciated.

There is another issue with this patchset (with and without the patch [1]).

[1] https://lore.kernel.org/lkml/20200803133657.GA13307@hori.linux.bs1.fc.nec.co.jp/

Arm64 using 512M-size hugepages starts to fail allocations prematurely.

# ./random 1
- start: migrate_huge_offline
- use NUMA nodes 0,1.
- mmap and free 2147483648 bytes hugepages on node 0
- mmap and free 2147483648 bytes hugepages on node 1
madvise: Cannot allocate memory

[  284.388061][ T3706] soft offline: 0x956000: hugepage isolation failed: 0, page count 2, type 17ffff80001000e (referenced|uptodate|dirty|head)
[  284.400777][ T3706] Soft offlining pfn 0x8e000 at process virtual address 0xffff80000000
[  284.893412][ T3706] Soft offlining pfn 0x8a000 at process virtual address 0xffff60000000
[  284.901539][ T3706] soft offline: 0x8a000: hugepage isolation failed: 0, page count 2, type 7ffff80001000e (referenced|uptodate|dirty|head)
[  284.914129][ T3706] Soft offlining pfn 0x8c000 at process virtual address 0xffff80000000
[  285.433497][ T3706] Soft offlining pfn 0x88000 at process virtual address 0xffff60000000
[  285.720377][ T3706] Soft offlining pfn 0x8a000 at process virtual address 0xffff80000000
[  286.281620][ T3706] Soft offlining pfn 0xa000 at process virtual address 0xffff60000000
[  286.290065][ T3706] soft offline: 0xa000: hugepage migration failed -12, type 7ffff80001000e (referenced|uptodate|dirty|head)

Reverting this patchset and its dependency patchset [2] (reverting the
dependency alone did not help) fixed it,

# ./random 1
- start: migrate_huge_offline
- use NUMA nodes 0,1.
- mmap and free 2147483648 bytes hugepages on node 0
- mmap and free 2147483648 bytes hugepages on node 1
- pass: mmap_offline_node_huge

[2] https://lore.kernel.org/linux-mm/1594622517-20681-1-git-send-email-iamjoonsoo.kim@lge.com/ 

> 
> Thanks,
> Naoya Horiguchi
> ---
> Previous versions:
>   v1: https://lore.kernel.org/linux-mm/1541746035-13408-1-git-send-email-n-horiguchi@ah.jp.nec.com/
>   v2: https://lore.kernel.org/linux-mm/20191017142123.24245-1-osalvador@suse.de/
>   v3: https://lore.kernel.org/linux-mm/20200624150137.7052-1-nao.horiguchi@gmail.com/
>   v4: https://lore.kernel.org/linux-mm/20200716123810.25292-1-osalvador@suse.de/
> ---
> Summary:
> 
> Naoya Horiguchi (8):
>       mm,hwpoison: cleanup unused PageHuge() check
>       mm, hwpoison: remove recalculating hpage
>       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,hwpoison: remove flag argument from soft offline functions
>       mm,hwpoison: introduce MF_MSG_UNSPLIT_THP
>       mm,hwpoison: double-check page count in __get_any_page()
> 
> Oscar Salvador (8):
>       mm,madvise: Refactor madvise_inject_error
>       mm,hwpoison: Un-export get_hwpoison_page and make it static
>       mm,hwpoison: Kill put_hwpoison_page
>       mm,hwpoison: Unify THP handling for hard and soft offline
>       mm,hwpoison: Rework soft offline for free pages
>       mm,hwpoison: Rework soft offline for in-use pages
>       mm,hwpoison: Refactor soft_offline_huge_page and __soft_offline_page
>       mm,hwpoison: Return 0 if the page is already poisoned in soft-offline
> 
>  drivers/base/memory.c      |   2 +-
>  include/linux/mm.h         |  12 +-
>  include/linux/page-flags.h |   6 +-
>  include/ras/ras_event.h    |   3 +
>  mm/hwpoison-inject.c       |  18 +--
>  mm/madvise.c               |  39 +++---
>  mm/memory-failure.c        | 334 ++++++++++++++++++++-------------------------
>  mm/migrate.c               |  11 +-
>  mm/page_alloc.c            |  60 ++++++--
>  9 files changed, 233 insertions(+), 252 deletions(-)

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