linux-kernel - Re: [RFC][PATCH v1 02/11] mm: soft-offline: add missing error check of set_hwpoison_free_buddy

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Date:   Fri, 9 Nov 2018 15:50:41 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Naoya Horiguchi <n-horiguchi@...jp.nec.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Cc:     Michal Hocko <mhocko@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        xishi.qiuxishi@...baba-inc.com,
        Laurent Dufour <ldufour@...ux.vnet.ibm.com>
Subject: Re: [RFC][PATCH v1 02/11] mm: soft-offline: add missing error check
 of set_hwpoison_free_buddy_page()

On 11/09/2018 12:17 PM, Naoya Horiguchi wrote:
> set_hwpoison_free_buddy_page() could fail, then the target page is
> finally not isolated, so it's better to report -EBUSY for userspace
> to know the failure and chance of retry.
> 

IIUC set_hwpoison_free_buddy_page() could only fail if the page is not
free in the buddy. At least for soft_offline_huge_page() that wont be
the case otherwise dissolve_free_huge_page() would have returned non
zero -EBUSY. Is there any other reason set_hwpoison_free_buddy_page()
would not succeed ?

> And for consistency, this patch moves set_hwpoison_free_buddy_page()
> in unmap_and_move() to __soft_offline_page().

Yeah this check should be handled in soft offline functions not inside
migrations they trigger.