linux-ext4 - Re: [PATCH 07/12] mm: Remove redundant pXd

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Message-ID: <20250529125435.00001378@huawei.com>
Date: Thu, 29 May 2025 12:54:35 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Alistair Popple <apopple@...dia.com>
CC: <linux-mm@...ck.org>, <gerald.schaefer@...ux.ibm.com>,
	<dan.j.williams@...el.com>, <jgg@...pe.ca>, <willy@...radead.org>,
	<david@...hat.com>, <linux-kernel@...r.kernel.org>, <nvdimm@...ts.linux.dev>,
	<linux-fsdevel@...r.kernel.org>, <linux-ext4@...r.kernel.org>,
	<linux-xfs@...r.kernel.org>, <jhubbard@...dia.com>, <hch@....de>,
	<zhang.lyra@...il.com>, <debug@...osinc.com>, <bjorn@...nel.org>,
	<balbirs@...dia.com>, <lorenzo.stoakes@...cle.com>,
	<linux-arm-kernel@...ts.infradead.org>, <loongarch@...ts.linux.dev>,
	<linuxppc-dev@...ts.ozlabs.org>, <linux-riscv@...ts.infradead.org>,
	<linux-cxl@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
	<John@...ves.net>
Subject: Re: [PATCH 07/12] mm: Remove redundant pXd_devmap calls

On Thu, 29 May 2025 16:32:08 +1000
Alistair Popple <apopple@...dia.com> wrote:

> DAX was the only thing that created pmd_devmap and pud_devmap entries
> however it no longer does as DAX pages are now refcounted normally and
> pXd_trans_huge() returns true for those. Therefore checking both pXd_devmap
> and pXd_trans_huge() is redundant and the former can be removed without
> changing behaviour as it will always be false.
> 
> Signed-off-by: Alistair Popple <apopple@...dia.com>

> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 8d9d706..31b4110 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1398,10 +1398,7 @@ static int insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
>  	}
>  
>  	entry = pmd_mkhuge(pfn_t_pmd(pfn, prot));
> -	if (pfn_t_devmap(pfn))

Didn't this go away in patch 5?  I didn't check but this looks like a bisectability issue.

> -		entry = pmd_mkdevmap(entry);
> -	else
> -		entry = pmd_mkspecial(entry);
> +	entry = pmd_mkspecial(entry);
>  	if (write) {
>  		entry = pmd_mkyoung(pmd_mkdirty(entry));
>  		entry = maybe_pmd_mkwrite(entry, vma);