linux-kernel - Re: [PATCH v6 16/26] huge_memory: Add vmf_insert_folio

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Message-ID: <6785c61e79bb5_20fa294f9@dwillia2-xfh.jf.intel.com.notmuch>
Date: Mon, 13 Jan 2025 18:04:14 -0800
From: Dan Williams <dan.j.williams@...el.com>
To: Alistair Popple <apopple@...dia.com>, <akpm@...ux-foundation.org>,
	<dan.j.williams@...el.com>, <linux-mm@...ck.org>
CC: <alison.schofield@...el.com>, Alistair Popple <apopple@...dia.com>,
	<lina@...hilina.net>, <zhang.lyra@...il.com>,
	<gerald.schaefer@...ux.ibm.com>, <vishal.l.verma@...el.com>,
	<dave.jiang@...el.com>, <logang@...tatee.com>, <bhelgaas@...gle.com>,
	<jack@...e.cz>, <jgg@...pe.ca>, <catalin.marinas@....com>, <will@...nel.org>,
	<mpe@...erman.id.au>, <npiggin@...il.com>, <dave.hansen@...ux.intel.com>,
	<ira.weiny@...el.com>, <willy@...radead.org>, <djwong@...nel.org>,
	<tytso@....edu>, <linmiaohe@...wei.com>, <david@...hat.com>,
	<peterx@...hat.com>, <linux-doc@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
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	<linux-ext4@...r.kernel.org>, <linux-xfs@...r.kernel.org>,
	<jhubbard@...dia.com>, <hch@....de>, <david@...morbit.com>,
	<chenhuacai@...nel.org>, <kernel@...0n.name>, <loongarch@...ts.linux.dev>
Subject: Re: [PATCH v6 16/26] huge_memory: Add vmf_insert_folio_pmd()

Alistair Popple wrote:
> Currently DAX folio/page reference counts are managed differently to
> normal pages. To allow these to be managed the same as normal pages
> introduce vmf_insert_folio_pmd. This will map the entire PMD-sized folio
> and take references as it would for a normally mapped page.
> 
> This is distinct from the current mechanism, vmf_insert_pfn_pmd, which
> simply inserts a special devmap PMD entry into the page table without
> holding a reference to the page for the mapping.
> 
> Signed-off-by: Alistair Popple <apopple@...dia.com>
> 
> ---
> 
> Changes for v5:
>  - Minor code cleanup suggested by David
> ---
>  include/linux/huge_mm.h |  1 +-
>  mm/huge_memory.c        | 54 ++++++++++++++++++++++++++++++++++--------
>  2 files changed, 45 insertions(+), 10 deletions(-)
> 
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index 5bd1ff7..3633bd3 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -39,6 +39,7 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
>  
>  vm_fault_t vmf_insert_pfn_pmd(struct vm_fault *vmf, pfn_t pfn, bool write);
>  vm_fault_t vmf_insert_pfn_pud(struct vm_fault *vmf, pfn_t pfn, bool write);
> +vm_fault_t vmf_insert_folio_pmd(struct vm_fault *vmf, struct folio *folio, bool write);
>  vm_fault_t vmf_insert_folio_pud(struct vm_fault *vmf, struct folio *folio, bool write);
>  
>  enum transparent_hugepage_flag {
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 256adc3..d1ea76e 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1381,14 +1381,12 @@ static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
>  {
>  	struct mm_struct *mm = vma->vm_mm;
>  	pmd_t entry;
> -	spinlock_t *ptl;
>  
> -	ptl = pmd_lock(mm, pmd);

Apply this comment to the previous patch too, but I think this would be
more self-documenting as:

   lockdep_assert_held(pmd_lock(mm, pmd));

...to make it clear in this diff and into the future what the locking
constraints of this function are.

After that you can add:

Reviewed-by: Dan Williams <dan.j.williams@...el.com>