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

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Message-ID: <Z+VTHs0lp4TSA9L9@nvidia.com>
Date: Thu, 27 Mar 2025 10:31:10 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Pratyush Yadav <ptyadav@...zon.de>
Cc: Changyuan Lyu <changyuanl@...gle.com>, linux-kernel@...r.kernel.org,
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Subject: Re: [PATCH v5 09/16] kexec: enable KHO support for memory
 preservation

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.

Jason