linux-kernel - Re: [PATCH v2 3/4] mm/migration: return errno when isolate_huge

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Message-ID: <a8c3707f-1e8b-5f1f-767b-5a47cd71d5ef@huawei.com>
Date:   Mon, 9 May 2022 16:03:04 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     David Hildenbrand <david@...hat.com>
CC:     <ying.huang@...el.com>, <hch@....de>, <dhowells@...hat.com>,
        <cl@...ux.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>, <akpm@...ux-foundation.org>,
        <mike.kravetz@...cle.com>, <naoya.horiguchi@....com>
Subject: Re: [PATCH v2 3/4] mm/migration: return errno when isolate_huge_page
 failed

On 2022/4/29 18:08, David Hildenbrand wrote:
> On 25.04.22 15:27, 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. Also we make
>> the prototype of isolate_huge_page consistent with isolate_lru_page to
>> improve the readability.
>>
>> Fixes: e8db67eb0ded ("mm: migrate: move_pages() supports thp migration")
> 
> If this is a fix, what's the runtime effect of it?
> 
> You state "could confuse", which doesn't indicate an actual BUG to me.

The hugetlb page might not be migrated due to error while it's not reported in the __user *status.
So the caller might think all of the memory is migrated and thus does not retry to migrate the
hugetlb page in the next round. Is this too trival to bother adding a Fixes tag?

Thanks!

> 
>