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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 10/16] mm,hwpoison: Rework soft offline for free pages
Date: Tue, 22 Oct 2019 11:58:52 +0200
Message-ID: <20191022095852.GB20429@linux> (raw)
In-Reply-To: <20191022092256.GH9379@dhcp22.suse.cz>

On Tue, Oct 22, 2019 at 11:22:56AM +0200, Michal Hocko wrote:
> Hmm, that might be a misunderstanding on my end. I thought that it is
> the MCE handler to say whether the failure is recoverable or not. If yes
> then we can touch the content of the memory (that would imply the
> migration). Other than that both paths should be essentially the same,
> no? Well unrecoverable case would be essentially force migration failure
> path.
> 
> MADV_HWPOISON is explicitly documented to test MCE handling IIUC:
> : This feature is intended for testing of memory error-handling
> : code; it is available only if the kernel was configured with
> : CONFIG_MEMORY_FAILURE.
> 
> There is no explicit note about the type of the error that is injected
> but I think it is reasonably safe to assume this is a recoverable one.

MADV_HWPOISON stands for hard-offline.
MADV_SOFT_OFFLINE stands for soft-offline.

MADV_SOFT_OFFLINE (since Linux 2.6.33)
              Soft offline the pages in the range specified by addr and
              length.  The memory of each page in the specified range is
              preserved (i.e., when next accessed, the same content will be
              visible, but in a new physical page frame), and the original
              page is offlined (i.e., no longer used, and taken out of
              normal memory management).  The effect of the
              MADV_SOFT_OFFLINE operation is invisible to (i.e., does not
              change the semantics of) the calling process.

              This feature is intended for testing of memory error-handling
              code; it is available only if the kernel was configured with
              CONFIG_MEMORY_FAILURE.


But both follow different approaches.

I think it is up to some controlers to trigger soft-offline or hard-offline:

static void ghes_handle_memory_failure(struct acpi_hest_generic_data *gdata, int sev)
{
#ifdef CONFIG_ACPI_APEI_MEMORY_FAILURE
	...
        /* iff following two events can be handled properly by now */
        if (sec_sev == GHES_SEV_CORRECTED &&
            (gdata->flags & CPER_SEC_ERROR_THRESHOLD_EXCEEDED))
                flags = MF_SOFT_OFFLINE;
        if (sev == GHES_SEV_RECOVERABLE && sec_sev == GHES_SEV_RECOVERABLE)
                flags = 0;

        if (flags != -1)
                memory_failure_queue(pfn, flags);
	...
#endif
 }


static void memory_failure_work_func(struct work_struct *work)
{
	...
	for (;;) {
		spin_lock_irqsave(&mf_cpu->lock, proc_flags);
		gotten = kfifo_get(&mf_cpu->fifo, &entry);
		spin_unlock_irqrestore(&mf_cpu->lock, proc_flags);
		if (!gotten)
			break;
		if (entry.flags & MF_SOFT_OFFLINE)
			soft_offline_page(pfn_to_page(entry.pfn), entry.flags);
		else
			memory_failure(entry.pfn, entry.flags);
	}
 }

AFAICS, for hard-offline case, a recovered event would be if:

- the page to shut down is already free
- the page was unmapped

In some cases we need to kill the process if it holds dirty pages.

But we never migrate contents in hard-offline path.
I guess it is because we cannot really trust the contents anymore.


-- 
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 [this message]
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
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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