Re: [PATCH v4 4/4] RISC-V: Add arch functions to support hibernation/suspend-to-disk

From: Andrew Jones <ajones@ventanamicro.com>
To: JeeHeng Sia <jeeheng.sia@starfivetech.com>
Cc: "paul.walmsley@sifive.com" <paul.walmsley@sifive.com>,
	"palmer@dabbelt.com" <palmer@dabbelt.com>,
	"aou@eecs.berkeley.edu" <aou@eecs.berkeley.edu>,
	"linux-riscv@lists.infradead.org"
	<linux-riscv@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Leyfoon Tan <leyfoon.tan@starfivetech.com>,
	Mason Huo <mason.huo@starfivetech.com>
Subject: Re: [PATCH v4 4/4] RISC-V: Add arch functions to support hibernation/suspend-to-disk
Date: Fri, 3 Mar 2023 09:09:10 +0100	[thread overview]
Message-ID: <20230303080910.hfipcsrgyvppa6ex@orel> (raw)
In-Reply-To: <94325d78a0b74d8289b77ec743840941@EXMBX066.cuchost.com>

On Fri, Mar 03, 2023 at 01:53:19AM +0000, JeeHeng Sia wrote:
> Hi Andrew,
> 
> 
> > -----Original Message-----
> > From: Andrew Jones <ajones@ventanamicro.com>
...
> > I'm not sure why you don't just write a paragraph or two here in this
> > email thread explaining what "the answer" is. Anyway, feel free to
> > invite me to a call if you think it'd be easier to hash out that way.
> Thank you very much to free up time to join the call. It was very nice to talk to you over the conference call and I did learn a lot from you.
> Below is the summary of the experiment that benefit everyone:
> To avoid inspecting a huge log, the experiment was carried out on the Qemu with 512MB of memory (128000 pages). 
> During hibernation, there are 22770 pages (out of 128000 pages) were identified need to be stored to the disk. Those pages consists of the kernel text code, rodata, page table, stack/heap/kmalloc/vmalloc memory, user space app, rootfs.....etc. The number of pages need to be stored to the disk are depends on the "workload" on the system.
> When resume, only 21651 pages were assigned to the restore_pblist. The rest of the pages consists of meta_data pages and forbidden pages which were handled by the "resume kernel". Arch code will handle the pages assigned to the restore_pblist.
> From the experiment, we also know that the game that is activated before hibernation is still "alive" after resume from hibernation and can continue to play without problem.
>

Thank you, Jee Heng. Indeed it looks like the majority of the pages that
are selected for the suspend image end up on the PBE list. While we don't
have definitive "this page must be on the PBE list" type of result, I
agree that we shouldn't need to worry about the PBE list ever being empty.

Thanks,
drew

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