Re: [RFC PATCH v1 4/4] mm, memory_hotplug: fix inconsistent num_poisoned_pages on memory hotremove

From: Naoya Horiguchi <naoya.horiguchi@linux.dev>
To: Miaohe Lin <linmiaohe@huawei.com>
Cc: "HORIGUCHI NAOYA(堀口 直也)" <naoya.horiguchi@nec.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Mike Kravetz" <mike.kravetz@oracle.com>,
	"Yang Shi" <shy828301@gmail.com>,
	"Oscar Salvador" <osalvador@suse.de>,
	"Muchun Song" <songmuchun@bytedance.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Linux-MM <linux-mm@kvack.org>
Subject: Re: [RFC PATCH v1 4/4] mm, memory_hotplug: fix inconsistent num_poisoned_pages on memory hotremove
Date: Mon, 9 May 2022 22:34:53 +0900	[thread overview]
Message-ID: <20220509133453.GA2511740@u2004> (raw)
In-Reply-To: <4cae9c00-a048-2c0a-9a45-d7abb956fde7@huawei.com>

On Thu, Apr 28, 2022 at 03:16:01PM +0800, Miaohe Lin wrote:
> On 2022/4/28 12:05, HORIGUCHI NAOYA(堀口 直也) wrote:
> > On Thu, Apr 28, 2022 at 11:20:16AM +0800, Miaohe Lin wrote:
> >> On 2022/4/27 12:28, Naoya Horiguchi wrote:
> >>> From: Naoya Horiguchi <naoya.horiguchi@nec.com>
> >>>
> >>> When offlining memory section with hwpoisoned pages, the hwpoisons are
> >>> canceled. But num_poisoned_pages is not updated for that event, so the
> >>> counter becomes inconsistent.
> >>
> >> IIUC, this work is already done via clear_hwpoisoned_pages when __remove_pages.
> >> Or am I miss something?
> > 
> > Actually I had the same question when writing this patch, and found that
> > __remove_pages() seems to be called from device memory or HMM, but not from
> 
> It seems remove_memory (which calls __remove_pages) will be called as .detach callback of
> memory_device_handler in drivers/acpi/acpi_memhotplug.c. So the hwpoison info will also be
> clear for that memory ?

Sorry, you're right.  That code path also calls __remove_pages() and
clear_hwpoisoned_pages(). So most major usecases of memory hotremove seems
not to be affected by the reported problem.

Thanks,
Naoya Horiguchi