linux-kernel - Re: [PATCH] kho: add support for deferred struct page init

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Message-ID: <CA+CK2bDZPwYpUhksDLSbfVdVm5TYbh0XrOKRV=q4YjGpqH+Fwg@mail.gmail.com>
Date: Tue, 30 Dec 2025 11:18:12 -0500
From: Pasha Tatashin <pasha.tatashin@...een.com>
To: Mike Rapoport <rppt@...nel.org>
Cc: Pratyush Yadav <pratyush@...nel.org>, Evangelos Petrongonas <epetron@...zon.de>, 
	Alexander Graf <graf@...zon.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Jason Miu <jasonmiu@...gle.com>, linux-kernel@...r.kernel.org, 
	kexec@...ts.infradead.org, linux-mm@...ck.org, nh-open-source@...zon.com
Subject: Re: [PATCH] kho: add support for deferred struct page init

On Tue, Dec 30, 2025 at 11:16 AM Mike Rapoport <rppt@...nel.org> wrote:
>
> On Tue, Dec 30, 2025 at 11:05:05AM -0500, Pasha Tatashin wrote:
> > On Mon, Dec 29, 2025 at 4:03 PM Pratyush Yadav <pratyush@...nel.org> wrote:
> > >
> > > The magic is purely sanity checking. It is not used to decide anything
> > > other than to make sure this is actually a KHO page. I don't intend to
> > > change that. My point is, if we make sure the KHO pages are properly
> > > initialized during MM init, then restoring can actually be a very cheap
> > > operation, where you only do the sanity checking. You can even put the
> > > magic check behind CONFIG_KEXEC_HANDOVER_DEBUG if you want, but I think
> > > it is useful enough to keep in production systems too.
> >
> > It is part of a critical hotpath during blackout, should really be
> > behind CONFIG_KEXEC_HANDOVER_DEBUG
>
> Do you have the numbers? ;-)

The fastest reboot we can achieve is ~0.4s on ARM
(shutdown+purgatory+boot), let's not add anything to regress, as every
microsecond counts during blackout.

Pasha