linux-kernel - Re: [PATCH v3 3/4] arm64: kdump: support more than one crash kernel regions

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Date:   Mon, 15 Apr 2019 08:04:18 +0300
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     Chen Zhou <chenzhou10@...wei.com>
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        ebiederm@...ssion.com, catalin.marinas@....com,
        will.deacon@....com, akpm@...ux-foundation.org,
        ard.biesheuvel@...aro.org, horms@...ge.net.au,
        takahiro.akashi@...aro.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
        linux-mm@...ck.org, wangkefeng.wang@...wei.com
Subject: Re: [PATCH v3 3/4] arm64: kdump: support more than one crash kernel
 regions

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.