linux-kernel - Re: [PATCH 3/8] mm: Introduce PageUnaccepted() page type

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Message-ID: <z5r4y4gb2ld2qa3moa33rzxyuzpzuim5ga6kk6oc4n6exdri7h@f6qbgdjhuu2z>
Date: Fri, 9 Aug 2024 11:28:17 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: David Hildenbrand <david@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, 
	"Borislav Petkov (AMD)" <bp@...en8.de>, Mel Gorman <mgorman@...e.de>, Vlastimil Babka <vbabka@...e.cz>, 
	Tom Lendacky <thomas.lendacky@....com>, Mike Rapoport <rppt@...nel.org>, 
	"Matthew Wilcox (Oracle)" <willy@...radead.org>, Johannes Weiner <hannes@...xchg.org>, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/8] mm: Introduce PageUnaccepted() page type

On Tue, Aug 06, 2024 at 02:06:02PM +0200, David Hildenbrand wrote:
> On 05.08.24 16:59, Kirill A. Shutemov wrote:
> > The new page type allows physical memory scanners to detect unaccepted
> > memory and handle it accordingly.
> > 
> > The page type is serialized with zone lock.
> > 
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> > ---
> >   include/linux/page-flags.h | 3 +++
> >   mm/page_alloc.c            | 2 ++
> >   2 files changed, 5 insertions(+)
> > 
> > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> > index 5769fe6e4950..e19eac9c2b5c 100644
> > --- a/include/linux/page-flags.h
> > +++ b/include/linux/page-flags.h
> > @@ -943,6 +943,7 @@ enum pagetype {
> >   	PG_hugetlb	= 0x04000000,
> >   	PG_slab		= 0x02000000,
> >   	PG_zsmalloc	= 0x01000000,
> > +	PG_unaccepted	= 0x00800000,
> >   	PAGE_TYPE_BASE	= 0x80000000,
> > @@ -1076,6 +1077,8 @@ FOLIO_TEST_FLAG_FALSE(hugetlb)
> >   PAGE_TYPE_OPS(Zsmalloc, zsmalloc, zsmalloc)
> > +PAGE_TYPE_OPS(Unaccepted, unaccepted, unaccepted)
> 
> I'm sure you're able to come up with some documentation ;)

Will do.

> > +
> >   /**
> >    * PageHuge - Determine if the page belongs to hugetlbfs
> >    * @page: The page to test.
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 90a1f01d5996..a35efb114496 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -6972,6 +6972,7 @@ static bool try_to_accept_memory_one(struct zone *zone)
> >   	account_freepages(zone, -MAX_ORDER_NR_PAGES, MIGRATE_MOVABLE);
> >   	__mod_zone_page_state(zone, NR_UNACCEPTED, -MAX_ORDER_NR_PAGES);
> > +	__ClearPageUnaccepted(page);
> >   	spin_unlock_irqrestore(&zone->lock, flags);
> >   	accept_page(page, MAX_PAGE_ORDER);
> > @@ -7030,6 +7031,7 @@ static bool __free_unaccepted(struct page *page)
> >   	list_add_tail(&page->lru, &zone->unaccepted_pages);
> >   	account_freepages(zone, MAX_ORDER_NR_PAGES, MIGRATE_MOVABLE);
> >   	__mod_zone_page_state(zone, NR_UNACCEPTED, MAX_ORDER_NR_PAGES);
> > +	__SetPageUnaccepted(page);
> >   	spin_unlock_irqrestore(&zone->lock, flags);
> >   	if (first)
> 
> At the point PG_unaccepted is set/cleared, we don't have another type set,
> right? (IOW, PG_buddy is only set after we cleared PG_unaccepted)

Right. PG_buddy is set after we clear PG_unaccepted.

There's brief period when the page is under accept when PG_unaccepted
already cleared, but PG_buddy is not yet set. But I don't think it can be
problematic.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov