linux-kernel - Re: [PATCH] mm,hwpoison: Return -EBUSY when migration fails

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Date:   Wed, 9 Dec 2020 11:25:31 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Oscar Salvador <osalvador@...e.de>, akpm@...ux-foundation.org
Cc:     n-horiguchi@...jp.nec.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH] mm,hwpoison: Return -EBUSY when migration fails

On 12/9/20 10:28 AM, Oscar Salvador wrote:
> Currently, we return -EIO when we fail to migrate the page.
> 
> Migrations' failures are rather transient as they can happen due to
> several reasons, e.g: high page refcount bump, mapping->migrate_page
> failing etc.
> All meaning that at that time the page could not be migrated, but
> that has nothing to do with an EIO error.
> 
> Let us return -EBUSY instead, as we do in case we failed to isolate
> the page.
> 
> While are it, let us remove the "ret" print as its value does not change.
> 
> Signed-off-by: Oscar Salvador <osalvador@...e.de>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

Technically this affects madvise(2) so let's cc linux-api. The manpage doesn't
document error codes of MADV_HWPOISON and MADV_SOFT_OFFLINE (besides EPERM)
though so nothing to adjust there. It's meant only for the hwpoison testing
suite anyway.

> ---
>  mm/memory-failure.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 428991e297e2..1942fb83ac64 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1849,11 +1849,11 @@ static int __soft_offline_page(struct page *page)
>  			pr_info("soft offline: %#lx: %s migration failed %d, type %lx (%pGp)\n",
>  				pfn, msg_page[huge], ret, page->flags, &page->flags);
>  			if (ret > 0)
> -				ret = -EIO;
> +				ret = -EBUSY;
>  		}
>  	} else {
> -		pr_info("soft offline: %#lx: %s isolation failed: %d, page count %d, type %lx (%pGp)\n",
> -			pfn, msg_page[huge], ret, page_count(page), page->flags, &page->flags);
> +		pr_info("soft offline: %#lx: %s isolation failed, page count %d, type %lx (%pGp)\n",
> +			pfn, msg_page[huge], page_count(page), page->flags, &page->flags);
>  		ret = -EBUSY;
>  	}
>  	return ret;
>