From: Hua Ji <hji@netscreen.com>
To: linux-mm@kvack.org
Subject: About performance related to do_map
Date: Tue, 15 May 2001 10:13:30 -0700 [thread overview]
Message-ID: <A33AEFDC2EC0D411851900D0B73EBEF766DBEB@NAPA> (raw)
Folks,
When reading source codes, get a question. Thanks in advance.
Function do_map() ./mm/mmap.c,
After/if we get a vma by using **get_unmapped_area**, why we still
double-check
the vma area by using do_munmap()?
This call to do_munmap()is ONLY NECESSARY when (flags & MAP_FIXED) is
**TRUE**.
The do_munmap will bring some EXTRA cost with the look up the vma linked
list or/and AVL tree.
Also, why not check it first before we create a new vma area? We don't have
to create a vma first and then release it afterwards when lateron we find
out that this vma is overlapped by some other vma area already.
Mike
------------------------------------------------
/* Obtain the address to map to. we verify (or select) it and ensure
* that it represents a valid section of the address space.
*/
if (flags & MAP_FIXED) {
if (addr & ~PAGE_MASK)
return -EINVAL;
} else {
addr = get_unmapped_area(addr, len);
if (!addr)
return -ENOMEM;
}
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux.eu.org/Linux-MM/
reply other threads:[~2001-05-15 17:00 UTC|newest]
Thread overview: [no followups] expand[flat|nested] mbox.gz Atom feed
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=A33AEFDC2EC0D411851900D0B73EBEF766DBEB@NAPA \
--to=hji@netscreen.com \
--cc=linux-mm@kvack.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