Message-ID: <bac3664f-a961-48bd-b642-368b128bb174@redhat.com>
Date: Tue, 1 Jul 2025 10:11:10 +0200
From: David Hildenbrand <david@...hat.com>
To: Harry Yoo <harry.yoo@...cle.com>, Zi Yan <ziy@...dia.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
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Subject: Re: [PATCH v1 05/29] mm/balloon_compaction: make PageOffline sticky
 until the page is freed

On 01.07.25 08:13, Harry Yoo wrote:
> On Mon, Jun 30, 2025 at 12:14:01PM -0400, Zi Yan wrote:
>> On 30 Jun 2025, at 12:01, Lorenzo Stoakes wrote:
>>
>>> On Mon, Jun 30, 2025 at 02:59:46PM +0200, David Hildenbrand wrote:
>>>> Let the page freeing code handle clearing the page type.
>>>
>>> Why is this advantageous? We want to keep the page marked offline for longer?
>>>
>>>>
>>>> Acked-by: Zi Yan <ziy@...dia.com>
>>>> Acked-by: Harry Yoo <harry.yoo@...cle.com>
>>>> Signed-off-by: David Hildenbrand <david@...hat.com>
>>>
>>> On assumption this UINT_MAX stuff is sane :)) I mean this is straightforward I
>>> guess:
>>
>> This is how page type is cleared.
>> See: https://elixir.bootlin.com/linux/v6.15.4/source/include/linux/page-flags.h#L1013.
>>
>> I agree with you that patch 4 should have a comment in free_pages_prepare()
>> about what the code is for and why UINT_MAX is used.
> 
> Or instead of comment, maybe something like this:
> 
> /* Clear any page type */
> static __always_inline void __ClearPageType(struct page *page)
> {
> 	VM_WARN_ON_ONCE_PAGE(!page_has_type(page), page);
> 	page->page_type = UINT_MAX;
> }
> 
> in patch 4:
> 
> if (unlikely(page_has_type(page)))
> 	__ClearPageType(page);
> 

I don't think we should do that. It's very specialized code that nobody 
should be reusing.

And it will all change once Willy reworks the page_type vs. _mapcount 
overlay.

-- 
Cheers,

David / dhildenb

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