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

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Message-ID: <aFMAQs25hGnAq-hn@casper.infradead.org>
Date: Wed, 18 Jun 2025 19:06:58 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Zi Yan <ziy@...dia.com>
Cc: David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-doc@...r.kernel.org,
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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 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.