From: riel@surriel.com (Rik van Riel)
To: kernelnewbies@lists.kernelnewbies.org
Subject: Regarding high mem
Date: Wed, 17 Oct 2012 17:00:58 -0400 [thread overview]
Message-ID: <507F1C8A.2080004@surriel.com> (raw)
In-Reply-To: <CAAqW7TPts5W91tUkR0axRr3szFEzHpbRZFgSsrjPoAVJyz=XmA@mail.gmail.com>
On 10/17/2012 04:52 AM, Kshemendra KP wrote:
> One thing not clear to me is, during boot, kernel is copied to 1st MB
> of the RAM in x86 architecture as this architecture
> has ISA mem map hole (640k -to 1MB). From 1st BM till 896MB is occupied
> by the kernel. Then user space will be
> made available beyond 896 MB. With this reasoning, it is not clear to
> me, whether user space which is present
> beyond 896 MB is in high memory.
You appear to be confusing virtual and physical memory.
Physical addresses 0 through 896MB are mapped at
virtual addresses 3GB through 3GB+896MB.
The 128MB above that are used for vmalloc, and a
few other miscellaneous things. This 1GB of
kernel virtual memory is the same in every process.
Virtual addresses 0-3GB are used for userspace,
which each process getting its own private 3GB
sized virtual memory area.
Ranges of process virtual memory can be used,
or unused. The used ranges could be backed by
any physical memory in the system (highmem, normal &
dma zones), or not by any memory at all (backed by
swap, or on-disk file pages).
Does that make sense?
prev parent reply other threads:[~2012-10-17 21:00 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-16 12:17 Regarding high mem Kshemendra KP
2012-10-16 18:00 ` Mulyadi Santosa
2012-10-17 8:34 ` Chetan Nanda
2012-10-17 8:52 ` Kshemendra KP
2012-10-17 13:56 ` Chetan Nanda
2012-10-17 21:00 ` Rik van Riel [this message]
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=507F1C8A.2080004@surriel.com \
--to=riel@surriel.com \
--cc=kernelnewbies@lists.kernelnewbies.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 a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).