Re: [PATCH 3/4] mm/migration: return errno when isolate_huge_page failed

From: Christoph Hellwig <hch@infradead.org>
To: Miaohe Lin <linmiaohe@huawei.com>
Cc: akpm@linux-foundation.org, mike.kravetz@oracle.com,
	shy828301@gmail.com, willy@infradead.org, ying.huang@intel.com,
	ziy@nvidia.com, minchan@kernel.org, apopple@nvidia.com,
	dave.hansen@linux.intel.com, o451686892@gmail.com,
	jhubbard@nvidia.com, peterx@redhat.com, naoya.horiguchi@nec.com,
	mhocko@suse.com, riel@redhat.com, osalvador@suse.de,
	david@redhat.com, sfr@canb.auug.org.au, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/4] mm/migration: return errno when isolate_huge_page failed
Date: Mon, 11 Apr 2022 07:10:50 -0700	[thread overview]
Message-ID: <YlQ26kP8zpCLWqwW@infradead.org> (raw)
In-Reply-To: <20220409073846.22286-4-linmiaohe@huawei.com>

On Sat, Apr 09, 2022 at 03:38:45PM +0800, Miaohe Lin wrote:
> We might fail to isolate huge page due to e.g. the page is under migration
> which cleared HPageMigratable. So we should return -EBUSY in this case
> rather than always return 1 which could confuse the user.
> 
> Fixes: e8db67eb0ded ("mm: migrate: move_pages() supports thp migration")
> Reviewed-by: Muchun Song <songmuchun@bytedance.com>
> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
> ---
>  mm/migrate.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 381963231a62..044656a14ae2 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1632,10 +1632,8 @@ static int add_page_for_migration(struct mm_struct *mm, unsigned long addr,
>  		goto out_putpage;
>  
>  	if (PageHuge(page)) {
> -		if (PageHead(page)) {
> -			isolate_huge_page(page, pagelist);
> -			err = 1;
> -		}
> +		if (PageHead(page))
> +			err = isolate_huge_page(page, pagelist) ? 1 : -EBUSY;

I think a:

			err = isolate_huge_page(page, pagelist);
			if (!err)
				err = 1;

would be a lot more readable here.