linux-kernel - Re: [PATCH v2 2/2] arm64: mmu: avoid allocating pages while installing ng-mapping for KPTI

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Message-ID: <aUO9M/oN+nx3nfW+@e129823.arm.com>
Date: Thu, 18 Dec 2025 08:37:07 +0000
From: Yeoreum Yun <yeoreum.yun@....com>
To: Ryan Roberts <ryan.roberts@....com>
Cc: catalin.marinas@....com, will@...nel.org, akpm@...ux-foundation.org,
	david@...nel.org, kevin.brodsky@....com, quic_zhenhuah@...cinc.com,
	dev.jain@....com, yang@...amperecomputing.com,
	chaitanyas.prakash@....com, bigeasy@...utronix.de,
	clrkwllms@...nel.org, rostedt@...dmis.org,
	lorenzo.stoakes@...cle.com, ardb@...nel.org, jackmanb@...gle.com,
	vbabka@...e.cz, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-rt-devel@...ts.linux.dev
Subject: Re: [PATCH v2 2/2] arm64: mmu: avoid allocating pages while
 installing ng-mapping for KPTI

[...]
> > I think it would be better to use only __GFP_HIGH in here since
> > when kpti_install_ng_mappings() is called, "kswpd" doesn't created yet.
> > and to allocate page with assurance, It would be good to use
> > min_reserved to.
> >
> > Am I missing something?
>
> Personally I think we should just use "GFP_KERNEL | __GFP_ZERO". Anything else
> would make this allocation look special, which it is not. If we fail to allocate
> at this point in boot, we have bigger problems.

But I'm not sure *HOW effective* to use GFP_KERNEL in here.
Since it's before the any filesystem inited.
IOW, in this context, almost there would be no *page cache*
and I think it seems meaningless to use "GFP_KERNEL" and "direct
reclaim"

So to get success for allocation, __GFP_HIGH | _GFP_ZERO seems much
better.

Thanks


--
Sincerely,
Yeoreum Yun