linux-kernel - Re: [PATCH v2 08/14] mm/khugepaged: Remove redundant pmd

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Message-ID: <31bdbfcf-bbfa-46b7-a427-806d42d88cec@redhat.com>
Date: Tue, 17 Jun 2025 11:44:30 +0200
From: David Hildenbrand <david@...hat.com>
To: Alistair Popple <apopple@...dia.com>, akpm@...ux-foundation.org
Cc: linux-mm@...ck.org, gerald.schaefer@...ux.ibm.com,
 dan.j.williams@...el.com, jgg@...pe.ca, willy@...radead.org,
 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,
 m.szyprowski@...sung.com, Jason Gunthorpe <jgg@...dia.com>
Subject: Re: [PATCH v2 08/14] mm/khugepaged: Remove redundant pmd_devmap()
 check

On 16.06.25 13:58, Alistair Popple wrote:
> The only users of pmd_devmap were device dax and fs dax. The check for
> pmd_devmap() in check_pmd_state() is therefore redundant as callers
> explicitly check for is_zone_device_page(), so this check can be dropped.
> 

Looking again, is this true?

If we return "SCAN_SUCCEED", we assume there is a page table there that 
we can map and walk.

But I assume we can drop that check because nobody will ever set 
pmd_devmap() anymore?

So likely just the description+sibject of this patch should be adjusted.

FWIW, I think check_pmd_state() should be changed to work on pmd_leaf() 
etc, but that's something for another day.

-- 
Cheers,

David / dhildenb