From: Chris Snook <csnook@redhat.com>
To: "James C. Georgas" <jgeorgas@georgas.ca>
Cc: linux-kernel@vger.kernel.org
Subject: Re: HIMEM calculation
Date: Mon, 03 Sep 2007 19:40:58 -0400 [thread overview]
Message-ID: <46DC9B8A.3060404@redhat.com> (raw)
In-Reply-To: <1188857974.6090.19.camel@Tachyon.home>
James C. Georgas wrote:
> I'm not sure I understand how the kernel calculates the amount of
> physical RAM it can map during the boot process.
>
> I've quoted two blocks of kernel messages below, one for a kernel with
> NOHIGHMEM and another for a kernel with HIGHMEM4G.
>
> If I do the math on the BIOS provided physical RAM map, there is less
> than 5MiB of the address space reserved. Since I only have 1GiB of
> physical RAM in the board, I figured that it would still be possible to
> physically map 1019MiB, even with the 3GiB/1GiB split between user space
> and kernel space that occurs with NOHIGHMEM.
>
> However, What actually happens is that I'm 127MiB short of a full GiB.
>
> What am I missing here? Why does that last 127MiB have to go in HIGHMEM?
That's the vmalloc address space. You only get 896 MB in the NORMAL
zone on i386, to leave room for vmalloc. If you don't like it, go 64-bit.
-- Chris
next prev parent reply other threads:[~2007-09-03 23:41 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-09-03 22:19 HIMEM calculation James C. Georgas
2007-09-03 23:40 ` Chris Snook [this message]
[not found] <491631.7157.qm@web88107.mail.re2.yahoo.com>
2007-09-04 12:48 ` Chris Snook
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=46DC9B8A.3060404@redhat.com \
--to=csnook@redhat.com \
--cc=jgeorgas@georgas.ca \
--cc=linux-kernel@vger.kernel.org \
/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.