From: David Hildenbrand <david@redhat.com>
To: Vlastimil Babka <vbabka@suse.cz>,
Miaohe Lin <linmiaohe@huawei.com>,
akpm@linux-foundation.org
Cc: iamjoonsoo.kim@lge.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/page_isolation: don't putback unisolated page
Date: Tue, 7 Sep 2021 11:56:20 +0200 [thread overview]
Message-ID: <80cfffdc-227e-c045-be74-1c08fb62c1e3@redhat.com> (raw)
In-Reply-To: <b4615b3c-8217-9f32-39c7-b91c9ec3cccb@suse.cz>
On 07.09.21 10:08, Vlastimil Babka wrote:
> On 9/6/21 14:49, David Hildenbrand wrote:
>> On 06.09.21 14:45, Miaohe Lin wrote:
>>> On 2021/9/6 20:11, David Hildenbrand wrote:
>>>> On 06.09.21 14:02, David Hildenbrand wrote:
>>>>> On 04.09.21 11:18, Miaohe Lin wrote:
>>>>>
>>>>> Thanks!
>>>>>
>>>>> Reviewed-by: David Hildenbrand <david@redhat.com>
>>>>>
>>>>
>>>> To make the confusion perfect (sorry) :D I tripple-checked:
>>>>
>>>> In unset_migratetype_isolate() we check that is_migrate_isolate_page(page) holds, otherwise we return.
>>>>
>>>> We call __isolate_free_page() only for such pages.
>>>>
>>>> __isolate_free_page() won't perform watermark checks on is_migrate_isolate().
>>>>
>>>> Consequently, __isolate_free_page() should never fail when called from unset_migratetype_isolate()
>>>>
>>>> If that's correct then we could instead maybe add a VM_BUG_ON() and a comment why this can't fail.
>>>>
>>>>
>>>> Makes sense or am I missing something?
>>>
>>> I think you're right. __isolate_free_page() should never fail when called from unset_migratetype_isolate()
>>> as explained by you. But it might be too fragile to reply on the failure conditions of __isolate_free_page().
>>> If that changes, VM_BUG_ON() here might trigger unexpectedly. Or am I just over-worried as failure conditions
>>> of __isolate_free_page() can hardly change?
>>
>> Maybe
>>
>> isolated_page = !!__isolate_free_page(page, order);
>> /*
>> * Isolating a free page in an isolated pageblock is expected to always
>> * work as watermarks don't apply here.
>> */
>> VM_BUG_ON(isolated_page);
>>
>>
>> VM_BUG_ON() allows us to detect any issues when testing. Combined with
>> the comment it tells everybody messing with __isolate_free_page() what
>> we expect in this function.
>>
>> In production system, we would handle it gracefully.
>
> If this can be handled gracefully, then I'd rather go with VM_WARN_ON.
> Maybe even WARN_ON_ONCE?
>
I think either VM_BUG_ON() or VM_WARN_ON() -- compiling the runtime
checks out -- should be good enough.
I'd just go with VM_BUG_ON(), because anybody messing with
__isolate_free_page() should clearly spot that we expect the current
handling. But no strong opinion.
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2021-09-07 9:56 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-04 9:18 [PATCH] mm/page_isolation: don't putback unisolated page Miaohe Lin
2021-09-06 9:40 ` David Hildenbrand
2021-09-06 11:32 ` Miaohe Lin
2021-09-06 11:50 ` David Hildenbrand
2021-09-06 12:01 ` David Hildenbrand
2021-09-06 12:08 ` Miaohe Lin
2021-09-06 12:02 ` David Hildenbrand
2021-09-06 12:11 ` David Hildenbrand
2021-09-06 12:45 ` Miaohe Lin
2021-09-06 12:49 ` David Hildenbrand
2021-09-07 1:46 ` Miaohe Lin
2021-09-07 9:52 ` David Hildenbrand
2021-09-07 8:08 ` Vlastimil Babka
2021-09-07 9:56 ` David Hildenbrand [this message]
2021-09-08 22:42 ` John Hubbard
2021-09-09 8:56 ` David Hildenbrand
2021-09-09 9:07 ` Vlastimil Babka
2021-09-09 9:37 ` David Hildenbrand
2021-09-09 16:50 ` John Hubbard
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