From: "H. Peter Anvin" <hpa@zytor.com>
To: Yinghai Lu <yinghai@kernel.org>
Cc: Lin Feng <linfeng@cn.fujitsu.com>,
akpm@linux-foundation.org, linux-mm@kvack.org, x86@kernel.org,
linux-kernel@vger.kernel.org, tglx@linutronix.de,
mingo@redhat.com, penberg@kernel.org, jacob.shin@amd.com
Subject: Re: [PATCH] x86: mm: accurate the comments for STEP_SIZE_SHIFT macro
Date: Mon, 18 Mar 2013 15:50:30 -0700 [thread overview]
Message-ID: <51479A36.3050600@zytor.com> (raw)
In-Reply-To: <CAE9FiQU2iqx=9LEx_u6J5O_kQ-5Lo6DTgSgnk71k0p6WWUa7Hg@mail.gmail.com>
On 03/18/2013 02:19 PM, Yinghai Lu wrote:
> On Mon, Mar 18, 2013 at 12:14 PM, H. Peter Anvin <hpa@zytor.com> wrote:
>
>> Instead, try to explain why 5 is the correct value in the current code
>> and how it is (or should be!) derived.
>
> initial mapped size is PMD_SIZE, aka 2M.
> if we use step_size to be PUD_SIZE aka 1G, as most worse case
> that 1G is cross the 1G boundary, and PG_LEVEL_2M is not set,
> we will need 1+1+512 pages (aka 2M + 8k) to map 1G range with PTE.
> So i picked (30-21)/2 to get 5.
>
> Please check attached patch.
>
> Thanks
>
> Yinghai
>
This still seems very opaque. I need to look at it and see if it makes
more sense in context.
-hpa
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prev parent reply other threads:[~2013-03-18 22:50 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-03-18 10:21 Lin Feng
2013-03-18 18:53 ` Yinghai Lu
2013-03-18 18:59 ` H. Peter Anvin
2013-03-18 19:13 ` Yinghai Lu
2013-03-18 19:14 ` H. Peter Anvin
2013-03-18 21:19 ` Yinghai Lu
2013-03-18 22:50 ` H. Peter Anvin [this message]
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