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

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Message-Id: <20231229121052.cac37914c7a051b829fcf933@linux-foundation.org>
Date: Fri, 29 Dec 2023 12:10:52 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Baoquan He <bhe@...hat.com>
Cc: Yuntao Wang <ytcoode@...il.com>, 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()

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?

Thanks.