linux-kernel - Re: [PATCH 4/5] mm: Make pgoff non-const in struct vm

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Date: Tue, 26 Mar 2024 02:38:00 +0000
From: Matthew Wilcox <willy@...radead.org>
To: "Vishal Moola (Oracle)" <vishal.moola@...il.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, muchun.song@...ux.dev
Subject: Re: [PATCH 4/5] mm: Make pgoff non-const in struct vm_fault

On Mon, Mar 25, 2024 at 03:33:38PM -0700, Vishal Moola (Oracle) wrote:
> Hugetlb calculates addresses and page offsets differently from the rest of
> mm. In order to pass struct vm_fault through the fault pathway we will let
> hugetlb_fault() and __handle_mm_fault() set those variables themselves
> instead.

I don't think this is a great idea.  I'd rather not do patch 5 than do
patch 4+5.  If you look at the history, commits 742d33729a0df11 and
5857c9209ce58f show that drivers got into the bad habit of changing
address & pgoff, so they got made const to prevent that.

So can we make hugetlbfs OK with using addresses & pgoffsets that aren't
aligned to HPAGE boundaries?  Worth playing with for a bit to see how
deep that assumption runs.