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

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Date: Tue, 26 Mar 2024 13:06:19 -0700
From: Vishal Moola <vishal.moola@...il.com>
To: Matthew Wilcox <willy@...radead.org>
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 7:38 PM Matthew Wilcox <willy@...radead.org> wrote:
>
> 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.

Hmmm, I'll take a look. I don't think there should be too many issues
with that.