linux-kernel - 回复: 回复: [PATCH] mm: optimize memblock_add

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Message-ID:
 <BYAPR12MB32052474A9C76EE2FBDCE707D5FD2@BYAPR12MB3205.namprd12.prod.outlook.com>
Date: Tue, 11 Feb 2025 03:32:23 +0000
From: Stephen Eta Zhou <stephen.eta.zhou@...look.com>
To: Mike Rapoport <rppt@...nel.org>
CC: "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject:
 回复: 回复: [PATCH] mm: optimize memblock_add_range() for improved performance

Hi Mike

> I doubt any optimization for memblock_add_range() will really improve boot
> time and even produce a measurable speed up.
> 
> With all the fragility and potential of breakage, I don't think it's
> worthwhile to attempt optimizations there.

Thank you for your insights. I appreciate your guidance on this matter, and after considering your advice, I have decided to stop pursuing further optimizations for the memblock_add_range() function. I'll follow your recommendation and focus on other areas that might offer more measurable improvements.

Best regards,
Stephen
________________________________________
发件人: Mike Rapoport <rppt@...nel.org>
发送时间: 2025年2月9日 21:53
收件人: Stephen Eta Zhou <stephen.eta.zhou@...look.com>
抄送: akpm@...ux-foundation.org <akpm@...ux-foundation.org>; linux-mm@...ck.org <linux-mm@...ck.org>; linux-kernel@...r.kernel.org <linux-kernel@...r.kernel.org>
主题: Re: 回复: [PATCH] mm: optimize memblock_add_range() for improved performance
 
Hi Stephen,

Please don't top post on Linux kernel mailing list.

On Fri, Feb 07, 2025 at 04:03:31PM +0000, Stephen Eta Zhou wrote:
> Hi Mike,
>
> Given the concerns raised, I would greatly appreciate your guidance on
> whether you think it's worthwhile for me to continue with this approach.
> Should I proceed with further refinements and testing, or would you
> recommend a different direction for optimization? Your input will be
> invaluable in ensuring this patch meets both performance and stability
> goals.

I doubt any optimization for memblock_add_range() will really improve boot
time and even produce a measurable speed up.

With all the fragility and potential of breakage, I don't think it's
worthwhile to attempt optimizations there.
 
> Best regards,  
> Stephen
> ________________________________________
> 发件人: Mike Rapoport <rppt@...nel.org>
> 发送时间: 2025年2月7日 22:58
> 收件人: Stephen Eta Zhou <stephen.eta.zhou@...look.com>
> 抄送: akpm@...ux-foundation.org <akpm@...ux-foundation.org>; linux-mm@...ck.org <linux-mm@...ck.org>; linux-kernel@...r.kernel.org <linux-kernel@...r.kernel.org>
> 主题: Re: [PATCH] mm: optimize memblock_add_range() for improved performance
>  
> Hi Stephen,
>
> On Wed, Feb 05, 2025 at 05:55:50AM +0000, Stephen Eta Zhou wrote:
> > Hi Mike Rapoport、Andrew Morton
>
> > I have recently been researching the mm subsystem of the Linux kernel,
> > and I came across the memblock_add_range function, which piqued my
> > interest. I found the implementation approach quite interesting, so I
> > analyzed it and identified some areas for optimization. Starting with
> > this part of the code:
> >
> > if (type->cnt * 2 + 1 <= type->max)
> >       insert = true;
> > The idea here is good, but it has a certain flaw. The condition is rather
> > restrictive, and it cannot be executed initially. Moreover, it is only
> > valid when the remaining space is (2/1) + 1. If there is enough memory,
> > but it does not satisfy (2/1) + 1, the insertion operation still needs to
> > be performed twice.
>
> The code in memblock_add_range() is very fragile, and many attempts to
> remove the second pass that looked correct at the first glance failed for
> some corner case.
>
> Unfortunately, it's impossible to capture all possible memory
> configurations and reservations in the memblock test suite, so even it it
> passes, there is a chance the kernel will fail to boot on an actual HW.
>  
> > - Before the patch:
> >   - Average: 1.22%
> >   - Max: 1.63%, Min: 0.93%
> >
> > - After the patch:
> >   - Average: 0.69%
> >   - Max: 0.94%, Min: 0.50%
> >
>
> These numbers do not represent what's actually interesting: the boot time
> speedup.
>
> --
> Sincerely yours,
> Mike.

--
Sincerely yours,
Mike.