linux-kernel - Re: [PATCH v2 3/9] mm/huge_memory: support huge zero folio in vmf_insert_folio

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Message-ID: <20250725080745.clm4s73fqtmsnqsn@master>
Date: Fri, 25 Jul 2025 08:07:45 +0000
From: Wei Yang <richard.weiyang@...il.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	xen-devel@...ts.xenproject.org, linux-fsdevel@...r.kernel.org,
	nvdimm@...ts.linux.dev, Andrew Morton <akpm@...ux-foundation.org>,
	Juergen Gross <jgross@...e.com>,
	Stefano Stabellini <sstabellini@...nel.org>,
	Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Matthew Wilcox <willy@...radead.org>, Jan Kara <jack@...e.cz>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...e.com>, Zi Yan <ziy@...dia.com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	Nico Pache <npache@...hat.com>, Ryan Roberts <ryan.roberts@....com>,
	Dev Jain <dev.jain@....com>, Barry Song <baohua@...nel.org>,
	Jann Horn <jannh@...gle.com>, Pedro Falcato <pfalcato@...e.de>,
	Hugh Dickins <hughd@...gle.com>, Oscar Salvador <osalvador@...e.de>,
	Lance Yang <lance.yang@...ux.dev>
Subject: Re: [PATCH v2 3/9] mm/huge_memory: support huge zero folio in
 vmf_insert_folio_pmd()

On Thu, Jul 17, 2025 at 01:52:06PM +0200, David Hildenbrand wrote:
>Just like we do for vmf_insert_page_mkwrite() -> ... ->
>insert_page_into_pte_locked() with the shared zeropage, support the
>huge zero folio in vmf_insert_folio_pmd().
>
>When (un)mapping the huge zero folio in page tables, we neither
>adjust the refcount nor the mapcount, just like for the shared zeropage.
>
>For now, the huge zero folio is not marked as special yet, although
>vm_normal_page_pmd() really wants to treat it as special. We'll change
>that next.
>
>Reviewed-by: Oscar Salvador <osalvador@...e.de>
>Signed-off-by: David Hildenbrand <david@...hat.com>
>---
> mm/huge_memory.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
>diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>index 849feacaf8064..db08c37b87077 100644
>--- a/mm/huge_memory.c
>+++ b/mm/huge_memory.c
>@@ -1429,9 +1429,11 @@ static vm_fault_t insert_pmd(struct vm_area_struct *vma, unsigned long addr,
> 	if (fop.is_folio) {
> 		entry = folio_mk_pmd(fop.folio, vma->vm_page_prot);
> 
>-		folio_get(fop.folio);
>-		folio_add_file_rmap_pmd(fop.folio, &fop.folio->page, vma);
>-		add_mm_counter(mm, mm_counter_file(fop.folio), HPAGE_PMD_NR);
>+		if (!is_huge_zero_folio(fop.folio)) {
>+			folio_get(fop.folio);
>+			folio_add_file_rmap_pmd(fop.folio, &fop.folio->page, vma);
>+			add_mm_counter(mm, mm_counter_file(fop.folio), HPAGE_PMD_NR);
>+		}

I think this is reasonable.

Reviewed-by: Wei Yang <richard.weiyang@...il.com>

> 	} else {
> 		entry = pmd_mkhuge(pfn_pmd(fop.pfn, prot));
> 		entry = pmd_mkspecial(entry);
>-- 
>2.50.1
>

-- 
Wei Yang
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