Re: [PATCH v6 00/12] HWPOISON: soft offline rework

From: Naoya Horiguchi <nao.horiguchi@gmail.com>
To: Qian Cai <cai@lca.pw>
Cc: "tony.luck@intel.com" <tony.luck@intel.com>,
	"david@redhat.com" <david@redhat.com>,
	"catalin.marinas@arm.com" <catalin.marinas@arm.com>,
	"zeil@yandex-team.ru" <zeil@yandex-team.ru>,
	"HORIGUCHI NAOYA(堀口　直也)" <naoya.horiguchi@nec.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"mhocko@kernel.org" <mhocko@kernel.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"aneesh.kumar@linux.vnet.ibm.com"
	<aneesh.kumar@linux.vnet.ibm.com>,
	"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
	"osalvador@suse.de" <osalvador@suse.de>,
	"will@kernel.org" <will@kernel.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	"mike.kravetz@oracle.com" <mike.kravetz@oracle.com>
Subject: Re: [PATCH v6 00/12] HWPOISON: soft offline rework
Date: Wed, 12 Aug 2020 04:32:01 +0900	[thread overview]
Message-ID: <20200811193201.GA1410457@u2004> (raw)
In-Reply-To: <20200811173923.GA39857@lca.pw>

On Tue, Aug 11, 2020 at 01:39:24PM -0400, Qian Cai wrote:
> On Tue, Aug 11, 2020 at 03:11:40AM +0000, HORIGUCHI NAOYA(堀口 直也) wrote:
> > I'm still not sure why the test succeeded by reverting these because
> > current mainline kernel provides similar mechanism to prevent reuse of
> > soft offlined page. So this success seems to me something suspicious.
> > 
> > To investigate more, I want to have additional info about the page states
> > of the relevant pages after soft offlining.  Could you collect it by the
> > following steps?
> > 
> >   - modify random.c not to run hotplug_memory() in migrate_huge_hotplug_memory(),
> >   - compile it and run "./random 1" once,
> >   - to collect page state with hwpoisoned pages, run "./page-types -Nlr -b hwpoison",
> >     where page-types is available under tools/vm in kernel source tree.
> >   - choose a few pfns of soft offlined pages from kernel message
> >     "Soft offlining pfn ...", and run "./page-types -Nlr -a <pfn>".
> 
> # ./page-types -Nlr -b hwpoison
> offset	len	flags
> 99a000	1	__________B________X_______________________
> 99c000	1	__________B________X_______________________
> 99e000	1	__________B________X_______________________
> 9a0000	1	__________B________X_______________________
> ba6000	1	__________B________X_______________________
> baa000	1	__________B________X_______________________

Thank you.  It only shows 6 lines of records, which is unexpected to me
because random.c iterates soft offline 2 hugepages with madvise() 1000 times.
Somehow (maybe in arch specific way?) other hwpoisoned pages might be cleared?
If they really are, the success of this test is a fake, and this patchset
can be considered as a fix.

> 
> Every single one of pfns was like this,
> 
> # ./page-types -Nlr -a 0x99a000
> offset	len	flags
> 99a000	1	__________B________X_______________________
> 
> # ./page-types -Nlr -a 0x99e000
> offset	len	flags
> 99e000	1	__________B________X_______________________
> 
> # ./page-types -Nlr -a 0x99c000
> offset	len	flags
> 99c000	1	__________B________X_______________________

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