From: "H. Peter Anvin" <hpa@zytor.com>
To: Youngwhan Song <breadncup@gmail.com>
Cc: Venkatram Tummala <venkatram867@gmail.com>,
Joel Fernandes <agnel.joel@gmail.com>,
Frank Hu <frank.hu.2001@gmail.com>,
hayfeng Lee <teklife.kernel@gmail.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-kernel@zh-kernel.org" <linux-kernel@zh-kernel.org>,
"kernelnewbies@nl.linux.org" <kernelnewbies@nl.linux.org>
Subject: Re: why choose 896MB to the start point of ZONE_HIGHMEM
Date: Tue, 06 Apr 2010 16:32:00 -0700 [thread overview]
Message-ID: <4BBBC470.4050002@zytor.com> (raw)
In-Reply-To: <3715922601579231267@unknownmsgid>
On 04/06/2010 04:27 PM, Youngwhan Song wrote:
> Nice explanation, Venkatram,
>
> Just one question pop up mind.
>
> What if actual physical memory is only 256MB? How does kernel divide
> virtual memory? Do we need to specify the region to kernel? Or will
> kernel itself decide it automatically?
>
If there is less than 896 MB of physical memory, the vmalloc region is
automatically extended (in your case, it will be 768 MB in size.) There
will be no HIGHMEM in such a case, and if you are compiling your own
kernel you will gain considerable speed by disabling HIGHMEM support
completely.
This, of course, was the norm back when Linux was first created, and a
typical amount of memory was 8 MB or so. That we'd have gigabytes of
memory seemed very distant at the time.
-hpa
next prev parent reply other threads:[~2010-04-06 23:41 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-04-06 14:37 why choose 896MB to the start point of ZONE_HIGHMEM hayfeng Lee
2010-04-06 15:02 ` Joel Fernandes
2010-04-06 18:17 ` H. Peter Anvin
2010-04-06 19:20 ` Frank Hu
2010-04-06 19:44 ` H. Peter Anvin
2010-04-06 20:01 ` Joel Fernandes
2010-04-06 20:04 ` H. Peter Anvin
[not found] ` <q2iacff6c2b1004061528t28f1337eq977aabf8fe71bc22@mail.gmail.com>
[not found] ` <3715922601579231267@unknownmsgid>
2010-04-06 23:32 ` H. Peter Anvin [this message]
2010-04-07 1:47 ` Xianghua Xiao
[not found] ` <n2uacff6c2b1004061904v5d290fa6v909e2e5fe32ff910@mail.gmail.com>
2010-04-07 2:09 ` H. Peter Anvin
[not found] ` <n2jacff6c2b1004062248w311d8482w6c64a7bdfded8385@mail.gmail.com>
2010-04-07 12:10 ` Xianghua Xiao
[not found] ` <k2z7f245da81004070550u5324f6ffyba3e996a3e292a0a@mail.gmail.com>
[not found] ` <n2kb114f3281004070948hb510b9b1o80126e2411a98c8d@mail.gmail.com>
2010-04-07 17:14 ` H. Peter Anvin
2010-04-08 2:23 ` Nobin Mathew
[not found] ` <u2o7f245da81004062105w1f7d3416n7855472d28e8bcfd@mail.gmail.com>
2010-04-07 5:28 ` H. Peter Anvin
[not found] ` <h2pacff6c2b1004062257mc8552d81u33322c43e47502c9@mail.gmail.com>
2010-04-07 6:04 ` H. Peter Anvin
[not found] ` <q2oc58e39921004062208z6410b031o8d5654a582cc2783@mail.gmail.com>
[not found] ` <t2yacff6c2b1004062309t89b6bddfy3b0cf5970846fbb0@mail.gmail.com>
2010-04-07 14:11 ` tek-life
2010-04-06 20:15 ` Frank Hu
2010-04-06 20:18 ` H. Peter Anvin
2010-04-07 12:16 ` Krzysztof Halasa
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=4BBBC470.4050002@zytor.com \
--to=hpa@zytor.com \
--cc=agnel.joel@gmail.com \
--cc=breadncup@gmail.com \
--cc=frank.hu.2001@gmail.com \
--cc=kernelnewbies@nl.linux.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-kernel@zh-kernel.org \
--cc=teklife.kernel@gmail.com \
--cc=venkatram867@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.