linux-kernel - Re: [PATCH v2] mm/mm_init: Don't iterate pages below ARCH_PFN

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Message-Id: <20250421112650.4fe689205944ccdaf078ca28@linux-foundation.org>
Date: Mon, 21 Apr 2025 11:26:50 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Mike Rapoport <rppt@...nel.org>
Cc: Ruihan Li <lrh2000@....edu.cn>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm/mm_init: Don't iterate pages below
 ARCH_PFN_OFFSET

On Mon, 21 Apr 2025 19:35:25 +0300 Mike Rapoport <rppt@...nel.org> wrote:

> On Sun, Apr 20, 2025 at 01:57:09PM -0700, Andrew Morton wrote:
> > On Sat, 19 Apr 2025 20:28:01 +0800 Ruihan Li <lrh2000@....edu.cn> wrote:
> > 
> > > If ARCH_PFN_OFFSET is very large (e.g., something like 2^64-2GiB if the
> > > kernel is used as a library and loaded at a very high address), the
> > > pointless iteration for pages below ARCH_PFN_OFFSET will take a very
> > > long time, and the kernel will look stuck at boot time.
> > > 
> > > This commit sets the initial value of pfn_hole to ARCH_PFN_OFFSET, which
> > > avoids the problematic and useless iteration mentioned above.
> > > 
> > > This problem has existed since commit 907ec5fca3dc ("mm: zero remaining
> > > unavailable struct pages").
> > > 
> > > Signed-off-by: Ruihan Li <lrh2000@....edu.cn>
> > > ---
> > > Link to v1:
> > >  - https://lore.kernel.org/linux-mm/20250418162727.1535335-1-lrh2000@pku.edu.cn/
> > > Changes since v1:
> > >  - Removed the unnecessary Fixes tag.
> > 
> > Why was the Fixes: considered unnecessary?  It seems to be useful
> > information?
> 
> I didn't think it was important enough for AUTOSEL to pick it. 

They've been asked not to backport MM patches unless they have an
explicit cc:stable.