Date:   Mon, 3 Aug 2020 21:49:42 -0400
From:   Qian Cai <cai@....pw>
To:     HORIGUCHI NAOYA(堀口　直也) 
        <naoya.horiguchi@....com>
Cc:     "nao.horiguchi@...il.com" <nao.horiguchi@...il.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "mhocko@...nel.org" <mhocko@...nel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "mike.kravetz@...cle.com" <mike.kravetz@...cle.com>,
        "osalvador@...e.de" <osalvador@...e.de>,
        "tony.luck@...el.com" <tony.luck@...el.com>,
        "david@...hat.com" <david@...hat.com>,
        "aneesh.kumar@...ux.vnet.ibm.com" <aneesh.kumar@...ux.vnet.ibm.com>,
        "zeil@...dex-team.ru" <zeil@...dex-team.ru>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 00/16] HWPOISON: soft offline rework

On Tue, Aug 04, 2020 at 01:16:45AM +0000, HORIGUCHI NAOYA(堀口 直也) wrote:
> On Mon, Aug 03, 2020 at 03:07:09PM -0400, Qian Cai wrote:
> > 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)
> 
> I think that this is due to the lack of contiguous memory.
> This test program iterates soft offlining many times for hugepages,
> so finally one page in every 512MB will be removed from buddy, then we
> can't allocate hugepage any more even if we have enough free pages.
> This is not good for heavy hugepage users, but that should be intended.
> 
> It seems that random.c calls madvise(MADV_SOFT_OFFLINE) for 2 hugepages,
> and iterates it 1000 (==NR_LOOP) times, so if the system doesn't have
> enough memory to cover the range of 2000 hugepages (1000GB in the Arm64
> system), this ENOMEM should reproduce as expected.

Well, each iteration will mmap/munmap, so there should be no leaking. 

https://gitlab.com/cailca/linux-mm/-/blob/master/random.c#L376

It also seem to me madvise(MADV_SOFT_OFFLINE) does start to fragment memory
somehow, because after this "madvise: Cannot allocate memory" happened, I
immediately checked /proc/meminfo and then found no hugepage usage at all.

> 
> > 
> > Reverting this patchset and its dependency patchset [2] (reverting the
> > dependency alone did not help) fixed it,
> 
> But it's still not clear to me why this was not visible before this
> patchset, so I need more check for it.
> 
> Thanks,
> Naoya Horiguchi
> 
> > 
> > # ./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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