From: Dave Hansen <dave.hansen@intel.com>
To: Zhou Chengming <zhouchengming1@huawei.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Cc: akpm@linux-foundation.org, tj@kernel.org, guohanjun@huawei.com,
huawei.libin@huawei.com
Subject: Re: [PATCH] make __section_nr more efficient
Date: Wed, 20 Jul 2016 14:36:04 -0700 [thread overview]
Message-ID: <578FEEC4.9060209@intel.com> (raw)
In-Reply-To: <1468988310-11560-1-git-send-email-zhouchengming1@huawei.com>
On 07/19/2016 09:18 PM, Zhou Chengming wrote:
> When CONFIG_SPARSEMEM_EXTREME is disabled, __section_nr can get
> the section number with a subtraction directly.
Does this actually *do* anything?
It was a long time ago, but if I remember correctly, the entire loop in
__section_nr() goes away because root_nr==NR_SECTION_ROOTS, so
root_nr=1, and the compiler optimizes away the entire subtraction.
So this basically adds an #ifdef and gets us nothing, although it makes
the situation much more explicit. Perhaps the comment should say that
this works *and* is efficient because the compiler can optimize all the
extreme complexity away.
--
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-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2016-07-20 21:36 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-20 4:18 [PATCH] make __section_nr more efficient Zhou Chengming
2016-07-20 21:36 ` Dave Hansen [this message]
2016-07-21 1:55 ` zhouchengming
2016-07-21 14:38 ` Dave Hansen
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=578FEEC4.9060209@intel.com \
--to=dave.hansen@intel.com \
--cc=akpm@linux-foundation.org \
--cc=guohanjun@huawei.com \
--cc=huawei.libin@huawei.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=tj@kernel.org \
--cc=zhouchengming1@huawei.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 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).