linux-kernel - Re: [PATCH RFC 04/29] mm/page_alloc: allow for making page types sticky until freed

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Message-ID: <0CFA6160-04EA-45D6-AC50-D10D659F916E@nvidia.com>
Date: Wed, 18 Jun 2025 14:09:08 -0400
From: Zi Yan <ziy@...dia.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, linux-doc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
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 Arnd Bergmann <arnd@...db.de>,
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 Shakeel Butt <shakeel.butt@...ux.dev>
Subject: Re: [PATCH RFC 04/29] mm/page_alloc: allow for making page types
 sticky until freed

On 18 Jun 2025, at 14:06, Matthew Wilcox wrote:

> On Wed, Jun 18, 2025 at 02:04:18PM -0400, Zi Yan wrote:
>>> Let's allow for not clearing a page type before freeing a page to the
>>> buddy.
>>>
>>> We'll focus on having a type set on the first page of a larger
>>> allocation only.
>>>
>>> With this change, we can reliably identify typed folios even though
>>> they might be in the process of getting freed, which will come in handy
>>> in migration code (at least in the transition phase).
>
>>> +	if (unlikely(page_has_type(page)))
>>> +		page->page_type = UINT_MAX;
>>> +
>>>  	if (is_check_pages_enabled()) {
>>>  		if (free_page_is_bad(page))
>>>  			bad++;
>>> -- 
>>> 2.49.0
>>
>> How does this preserve page type? Isn’t page->page_type = UINT_MAX clearing
>> page_type?
>
> The point is that the _caller_ used to have to clear the page type.
> This patch allows the caller to free the page without clearing
> the page type first.

Yep, find that out when I read the next patch.

I think the change is fine, but the commit message is unclear.

Best Regards,
Yan, Zi