linux-kernel - Re: [PATCH 3/3] crash_core: fix and simplify the logic of crash_exclude_mem

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Date: Tue, 2 Jan 2024 16:41:17 +0800
From: Baoquan He <bhe@...hat.com>
To: Yuntao Wang <ytcoode@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, bp@...en8.de,
	dave.hansen@...ux.intel.com, dyoung@...hat.com,
	eric.devolder@...cle.com, hbathini@...ux.ibm.com, hpa@...or.com,
	kexec@...ts.infradead.org, lijiang@...hat.com,
	linux-kernel@...r.kernel.org, mingo@...hat.com, seanjc@...gle.com,
	sourabhjain@...ux.ibm.com, tglx@...utronix.de, tiwai@...e.de,
	vgoyal@...hat.com, x86@...nel.org
Subject: Re: [PATCH 3/3] crash_core: fix and simplify the logic of
 crash_exclude_mem_range()

Hi Yuntao,

On 12/30/23 at 06:16pm, Baoquan He wrote:
> On 12/29/23 at 12:10pm, Andrew Morton wrote:
> > On Sat, 16 Dec 2023 11:31:04 +0800 Baoquan He <bhe@...hat.com> wrote:
> > 
> > > > > Imagine we have a crashkernel region 256M reserved under 4G, say [2G, 2G+256M].
> > > > > Then after excluding the 256M from a region, it should stop. But now, this patch
> > > > > will make it continue scanning. Not sure if it's all in my mind.
> > > > 
> > > > Hi Baoquan,
> > > > 
> > > > Thank you for such a detailed reply. Now I finally understand why the code is
> > > > written this way.
> > > > 
> > > > However, if we can guarantee its correctness, wouldn't it be better to use the
> > > > generic region removing logic? At least it is more concise and clear, and other
> > > > people reading this code for the first time wouldn't get confused like me.
> > > > 
> > > > As for your concern about the while loop, I think it wouldn't affect performance
> > > > much because the total number of loops is small.
> > > 
> > > Well, see below kexec-tools commit, you wouldn't say that. And when you
> > > understand the code, you will feel a little uncomfortable about the
> > > sustaining useless scanning. At least, we should stop scanning after
> > > needed exluding is done.
> > > 
> > > Or, we may need add a generic region removing function so that it
> > > can be shared, e.g e820 memory region removing, memblock region removing.
> > > Otherwise, I can't see why a specific region excluding need a generic 
> > > region removing function.
> > 
> > So where do we now stand on this patchset?
> 
> The patch 1 and 2 are good clean up. The patch 3 plus below one, the
> entire is a good code improvement patch.
> 
> [PATCH] crash_core: optimize crash_exclude_mem_range()
> https://lore.kernel.org/all/20231219163418.108591-1-ytcoode@gmail.com/T/#u

Can you repost this patchset with some updating, e.g adding ack in patch
1 and 2, and squash below patch into patch 3? This will be easier for
patch merging.

[PATCH] crash_core: optimize crash_exclude_mem_range()
https://lore.kernel.org/all/20231219163418.108591-1-ytcoode@gmail.com/T/#u

And, you may need to drop below patchset since patch 2 conflicts with
this patchset, and patch 1 is conflicting with fuqiang's patch.

[PATCH 0/2] crash: fix potential cmem->ranges array overflow

Thanks
Baoquan