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Date:   Mon, 15 Apr 2019 08:04:18 +0300
From:   Mike Rapoport <rppt@linux.ibm.com>
To:     Chen Zhou <chenzhou10@huawei.com>
Cc:     tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
        ebiederm@xmission.com, catalin.marinas@arm.com,
        will.deacon@arm.com, akpm@linux-foundation.org,
        ard.biesheuvel@linaro.org, horms@verge.net.au,
        takahiro.akashi@linaro.org, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org, kexec@lists.infradead.org,
        linux-mm@kvack.org, wangkefeng.wang@huawei.com
Subject: Re: [PATCH v3 3/4] arm64: kdump: support more than one crash kernel
 regions
References: <20190409102819.121335-1-chenzhou10@huawei.com>
 <20190409102819.121335-4-chenzhou10@huawei.com>
 <20190410130917.GC17196@rapoport-lnx>
 <137bef2e-8726-fd8f-1cb0-7592074f7870@huawei.com>
 <20190414121058.GC20947@rapoport-lnx>
 <b5206f0c-d711-427e-256a-98b2e30c1ab0@huawei.com>
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Hi,

On Mon, Apr 15, 2019 at 10:05:18AM +0800, Chen Zhou wrote:
> Hi Mike,
> 
> On 2019/4/14 20:10, Mike Rapoport wrote:
> >>
> >> solution A: 	phys_addr_t start[INIT_MEMBLOCK_RESERVED_REGIONS * 2];
> >> 		phys_addr_t end[INIT_MEMBLOCK_RESERVED_REGIONS * 2];
> >> start, end is physical addr
> >>
> >> solution B: 	int start_rgn[INIT_MEMBLOCK_REGIONS], end_rgn[INIT_MEMBLOCK_REGIONS];
> >> start_rgn, end_rgn is rgn index		
> >>
> >> Solution B do less remove operations and with no warning comparing to solution A.
> >> I think solution B is better, could you give some suggestions?
> >  
> > Solution B is indeed better that solution A, but I'm still worried by
> > relatively large arrays on stack and the amount of loops :(
> > 
> > The very least we could do is to call memblock_cap_memory_range() to drop
> > the memory before and after the ranges we'd like to keep.
> 
> 1. relatively large arrays
> As my said above, the start_rgn, end_rgn is rgn index, we could use unsigned char type.

Let's stick to int for now

> 2. loops
> Loops always exist, and the solution with fewer loops may be just encapsulated well.

Of course the loops are there, I just hoped we could get rid of the nested
loop and get away with single passes in all the cases.
Apparently it's not the case :(

> Thanks,
> Chen Zhou
> 

-- 
Sincerely yours,
Mike.