linux-kernel - Re: [PATCH 2/2] kho: fix restoring of contiguous ranges of order-0 pages

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Message-ID: <aS07racwRsh4ep_L@kernel.org>
Date: Mon, 1 Dec 2025 08:54:37 +0200
From: Mike Rapoport <rppt@...nel.org>
To: Pratyush Yadav <pratyush@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Graf <graf@...zon.com>,
	Pasha Tatashin <pasha.tatashin@...een.com>,
	kexec@...ts.infradead.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] kho: fix restoring of contiguous ranges of order-0
 pages

Hi Pratyush,

On Tue, Nov 25, 2025 at 02:45:59PM +0100, Pratyush Yadav wrote:
> On Tue, Nov 25 2025, Mike Rapoport wrote:

...

> > @@ -243,11 +243,16 @@ static struct page *kho_restore_page(phys_addr_t phys)
> >  	/* Head page gets refcount of 1. */
> >  	set_page_count(page, 1);
> >  
> > -	/* For higher order folios, tail pages get a page count of zero. */
> > +	/*
> > +	 * For higher order folios, tail pages get a page count of zero.
> > +	 * For physically contiguous order-0 pages every pages gets a page
> > +	 * count of 1
> > +	 */
> > +	ref_cnt = is_folio ? 0 : 1;
> >  	for (unsigned int i = 1; i < nr_pages; i++)
> > -		set_page_count(page + i, 0);
> > +		set_page_count(page + i, ref_cnt);
> >  
> > -	if (info.order > 0)
> > +	if (is_folio && info.order)
> 
> This is getting a bit difficult to parse. Let's separate out folio and
> page initialization to separate helpers:
 
Sorry, I've missed this earlier and now the patches are in akpm's -stable
branch.
Let's postpone these changes for the next cycle, maybe along with support
for deferred initialization of struct page.

> 	/* Initalize 0-order KHO pages */
> 	static void kho_init_page(struct page *page, unsigned int nr_pages)
> 	{
> 		for (unsigned int i = 0; i < nr_pages; i++)
> 			set_page_count(page + i, 1);
> 	}
> 	
> 	static void kho_init_folio(struct page *page, unsigned int order)
> 	{
> 		unsigned int nr_pages = (1 << order);
> 	
> 		/* Head page gets refcount of 1. */
> 		set_page_count(page, 1);
> 	
> 		/* For higher order folios, tail pages get a page count of zero. */
> 		for (unsigned int i = 1; i < nr_pages; i++)
> 			set_page_count(page + i, 0);
> 	
> 		if (order > 0)
> 			prep_compound_page(page, order);
> 	}

-- 
Sincerely yours,
Mike.