From: Michal Hocko <mhocko@suse.com>
To: Oscar Salvador <osalvador@techadventures.net>
Cc: Wei Yang <richard.weiyang@gmail.com>,
akpm@linux-foundation.org, rientjes@google.com,
linux-mm@kvack.org, kirill.shutemov@linux.intel.com,
bob.picco@hp.com
Subject: Re: [PATCH 3/3] mm/sparse: use __highest_present_section_nr as the boundary for pfn check
Date: Thu, 23 Aug 2018 21:17:29 +0200 [thread overview]
Message-ID: <20180823191729.GQ29735@dhcp22.suse.cz> (raw)
In-Reply-To: <20180823140053.GC14924@techadventures.net>
On Thu 23-08-18 16:00:53, Oscar Salvador wrote:
> On Thu, Aug 23, 2018 at 03:25:26PM +0200, Michal Hocko wrote:
> > On Thu 23-08-18 21:07:32, Wei Yang wrote:
> > > And it is known, __highest_present_section_nr is a more strict boundary
> > > than NR_MEM_SECTIONS.
> > >
> > > This patch uses a __highest_present_section_nr to check a valid pfn.
> >
> > But why is this an improvement? Sure when you loop over all sections
> > than __highest_present_section_nr makes a lot of sense. But all the
> > updated function perform a trivial comparision.
>
> I think it makes some sense.
> NR_MEM_SECTIONS can be a big number, but we might not be using
> all sections, so __highest_present_section_nr ends up being a much lower
> value.
And how exactly does it help to check for the smaller vs. a larger number?
Both are O(1) operations AFAICS. __highest_present_section_nr makes
perfect sense when we iterate over all sections or similar operations
where it smaller number of iterations really makes sense.
I am not saying the patch is wrong but I just do not see this being an
improvement. You have to export an internal symbol to achieve something
that is hardly an optimization.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2018-08-23 19:17 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-23 13:07 [PATCH 0/3] trivial code refine for sparsemem Wei Yang
2018-08-23 13:07 ` [PATCH 1/3] mm/sparse: add likely to mem_section[root] check in sparse_index_init() Wei Yang
2018-08-23 13:13 ` Michal Hocko
2018-08-23 22:57 ` Wei Yang
2018-08-24 7:31 ` Michal Hocko
2018-08-24 0:11 ` Dave Hansen
2018-08-24 15:07 ` Wei Yang
2018-09-03 22:27 ` Wei Yang
2018-09-09 1:38 ` Wei Yang
2018-09-10 20:30 ` Dave Hansen
2018-09-11 15:00 ` Wei Yang
2018-08-23 13:07 ` [PATCH 2/3] mm/sparse: expand the CONFIG_SPARSEMEM_EXTREME range in __nr_to_section() Wei Yang
2018-08-23 13:21 ` Michal Hocko
2018-08-23 23:03 ` Wei Yang
2018-08-24 0:09 ` Dave Hansen
2018-08-24 15:24 ` Wei Yang
2018-08-23 13:07 ` [PATCH 3/3] mm/sparse: use __highest_present_section_nr as the boundary for pfn check Wei Yang
2018-08-23 13:25 ` Michal Hocko
2018-08-23 14:00 ` Oscar Salvador
2018-08-23 19:17 ` Michal Hocko [this message]
2018-08-23 20:52 ` Oscar Salvador
2018-08-24 0:15 ` Dave Hansen
2018-08-24 18:11 ` Wei Yang
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=20180823191729.GQ29735@dhcp22.suse.cz \
--to=mhocko@suse.com \
--cc=akpm@linux-foundation.org \
--cc=bob.picco@hp.com \
--cc=kirill.shutemov@linux.intel.com \
--cc=linux-mm@kvack.org \
--cc=osalvador@techadventures.net \
--cc=richard.weiyang@gmail.com \
--cc=rientjes@google.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