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

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Message-ID: <7eunuizzdfpgskxrfmngklrq632szzgscp6agwxsl7wsodpdqn@vnyg7d3v6tmh>
Date: Mon, 21 Apr 2025 17:35:46 +0800
From: Ruihan Li <lrh2000@....edu.cn>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Mike Rapoport <rppt@...nel.org>, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, Ruihan Li <lrh2000@....edu.cn>
Subject: Re: [PATCH v2] mm/mm_init: Don't iterate pages below ARCH_PFN_OFFSET

Hi Andrew,

Thanks for your review and for taking the patch in the -mm tree!

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?
> 

To clarify, I only removed it because I got comments saying that this
patch doesn't really fix a BUG (well, that statement depends on how one
defines a BUG: it's a real BUG in my scenario, but maybe not a BUG for
many other scenarios):
https://lore.kernel.org/linux-mm/aANN0rwxcajUtFXs@kernel.org/

Since I don't know if there are other rules that apply here, I followed
the review comments to remove it.

Another possibility is that I misunderstood Mike's original comment?
Sorry if that happens.

Thanks,
Ruihan Li