linux-kernel - Re: [PATCH v5 09/16] kexec: enable KHO support for memory preservation

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Message-ID: <20250402164453.2470750-1-changyuanl@google.com>
Date: Wed,  2 Apr 2025 09:44:53 -0700
From: Changyuan Lyu <changyuanl@...gle.com>
To: ptyadav@...zon.de
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Subject: Re: [PATCH v5 09/16] kexec: enable KHO support for memory preservation

Hi Pratyush, Thanks for suggestions!

On Thu, Mar 27, 2025 at 17:28:40 +0000, Pratyush Yadav <ptyadav@...zon.de> wrote:
> On Thu, Mar 27 2025, Jason Gunthorpe wrote:
>
> > On Thu, Mar 27, 2025 at 10:03:17AM +0000, Pratyush Yadav wrote:
> >
> >> Of course, with the current linked list structure, this cannot work. But
> >> I don't see why we need to have it. I think having a page-table like
> >> structure would be better -- only instead of having PTEs at the lowest
> >> levels, you have the bitmap.
> >
> > Yes, but there is a trade off here of what I could write in 30 mins
> > and what is maximally possible :) The xarray is providing a page table
> > implementation in a library form.
> >
> > I think this whole thing can be optimized, especially the
> > memblock_reserve side, but the idea here is to get started and once we
> > have some data on what the actual preservation workload is then
> > someone can optimize this.
> >
> > Otherwise we are going to be spending months just polishing this one
> > patch without any actual data on where the performance issues and hot
> > spots actually are.
>
> The memblock_reserve side we can optimize later, I agree. But the memory
> preservation format is ABI and I think that is worth spending a little
> more time on. And I don't think it should be that much more complex than
> the current format.
>
> I want to hack around with it, so I'll give it a try over the next few
> days and see what I can come up with.

I agree with Jason that "nothing is ABI at this
point" and it will take some time for KHO to stabilize.

On the other hand if you have already came up with something working and
simple, we can include it in the next version.

(Sorry for the late reply, I was traveling.)

Best,
Changyuan