linux-kernel - Re: [PATCH 4/6] x86, mm: make split_mem

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Message-ID: <alpine.DEB.2.21.1903280902390.1789@nanos.tec.linutronix.de>
Date:   Thu, 28 Mar 2019 09:08:43 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Wei Yang <richardw.yang@...ux.intel.com>
cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.or
Subject: Re: [PATCH 4/6] x86, mm: make split_mem_range() more easy to read

On Thu, 28 Mar 2019, Wei Yang wrote:
> On Sun, Mar 24, 2019 at 03:29:04PM +0100, Thomas Gleixner wrote:
> My question is to the for loop.
> 
> For example, we have a range
> 
>        +--+---------+-----------------------+
>        ^ 128M       1G                      2G
>    128M - 4K
> 
> If my understanding is correct, the original behavior will split this into
> three ranges:
> 
>    4K size: [128M - 4K, 128M]
>    2M size: [128M, 1G]
>    1G size: [1G, 2G]
> 
> While after your change, it will split this into two ranges:
> 
>    ?? size: [128M - 4K, 1G]
>    2M size: [1G, 2G]
>
> The question mark here is because you leave the page_size_mask unchanged in
> this case.
> 
> Is my understanding correct? Or I missed something?

Yes. You misread mr_try_map().

Thanks,

	tglx