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Date: Sat, 30 Dec 2023 18:16:36 +0800
From: Baoquan He <bhe@redhat.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Yuntao Wang <ytcoode@gmail.com>, bp@alien8.de,
	dave.hansen@linux.intel.com, dyoung@redhat.com,
	eric.devolder@oracle.com, hbathini@linux.ibm.com, hpa@zytor.com,
	kexec@lists.infradead.org, lijiang@redhat.com,
	linux-kernel@vger.kernel.org, mingo@redhat.com, seanjc@google.com,
	sourabhjain@linux.ibm.com, tglx@linutronix.de, tiwai@suse.de,
	vgoyal@redhat.com, x86@kernel.org
Subject: Re: [PATCH 3/3] crash_core: fix and simplify the logic of
 crash_exclude_mem_range()
Message-ID: <ZY/uBJmpG14Ogvet@MiWiFi-R3L-srv>
References: <ZXxtfpXpuFXLd+ge@MiWiFi-R3L-srv>
 <20231216015410.188924-1-ytcoode@gmail.com>
 <ZX0Z+IyaAX9lNSok@MiWiFi-R3L-srv>
 <20231229121052.cac37914c7a051b829fcf933@linux-foundation.org>
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In-Reply-To: <20231229121052.cac37914c7a051b829fcf933@linux-foundation.org>

On 12/29/23 at 12:10pm, Andrew Morton wrote:
> On Sat, 16 Dec 2023 11:31:04 +0800 Baoquan He <bhe@redhat.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