From: Dave Hansen <dave@linux.vnet.ibm.com>
To: Andrea Arcangeli <aarcange@redhat.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Michael J Wolf <mjwolf@us.ibm.com>
Subject: Re: [RFC][PATCH 0/6] more detailed per-process transparent hugepage statistics
Date: Tue, 01 Feb 2011 09:15:47 -0800 [thread overview]
Message-ID: <1296580547.27022.3370.camel@nimitz> (raw)
In-Reply-To: <20110201153857.GA18740@random.random>
On Tue, 2011-02-01 at 16:38 +0100, Andrea Arcangeli wrote:
> On Mon, Jan 31, 2011 at 04:33:57PM -0800, Dave Hansen wrote:
> > I'm working on some more reports that transparent huge pages and
> > KSM do not play nicely together. Basically, whenever THP's are
> > present along with KSM, there is a lot of attrition over time,
> > and we do not see much overall progress keeping THP's around:
> >
> > http://sr71.net/~dave/ibm/038_System_Anonymous_Pages.png
> >
> > (That's Karl Rister's graph, thanks Karl!)
>
> Well if the pages_sharing/pages_shared count goes up, this is a
> feature not a bug.... You need to print that too in the chart to show
> this is not ok
Here are the KSM sharing bits for the same run:
http://sr71.net/~dave/ibm/009_KSM_Pages.png
It bounces around a little bit on the ends, but it's fairly static
during the test, even when there's a good downward slope on the THP's.
Hot of the presses, Karl also managed to do a run last night with the
khugepaged scanning rates turned all the way up:
http://sr71.net/~dave/ibm/038_System_Anonymous_Pages-scan-always.png
The THP's there are a lot more stable. I'd read that as saying that the
scanning probably just isn't keeping up with whatever is breaking the
pages up.
> KSM will slowdown performance also during copy-on-writes when
> pages_sharing goes up, not only because of creating non-linearity
> inside 2m chunks (which makes mandatory to use ptes and not hugepmd,
> it's not an inefficiency of some sort that can be optimized away
> unfortunately). We sure could change KSM to merge 2M pages instead of
> 4k pages, but then the memory-density would decrease of several order
> of magnitudes making the KSM scan almost useless (ok, with guest
> heavily using THP that may change, but all pagecache is still 4k... so
> for now it'd be next to useless).
Yup, unless we do something special, the odds of sharing those 2MB
suckers are near zero.
> I would prefer to close the issues that you just previously reported,
> sometime with mmap_sem and issues like that, before adding more
> features though but I don't want to defer things either so it's up to
> you.
I'm happy to hold on to them for another release. I'm actually going to
go look at the freezes I saw now that I have these out in the wild.
I'll probably stick them in a git tree and keep them up to date.
Are there any other THP issues you're chasing at the moment?
-- Dave
--
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/ .
Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2011-02-01 17:16 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-02-01 0:33 [RFC][PATCH 0/6] more detailed per-process transparent hugepage statistics Dave Hansen
2011-02-01 0:33 ` [RFC][PATCH 1/6] count transparent hugepage splits Dave Hansen
2011-02-01 9:58 ` Johannes Weiner
2011-02-03 21:22 ` David Rientjes
2011-02-04 21:18 ` Andrea Arcangeli
2011-02-04 21:28 ` Dave Hansen
2011-02-01 0:33 ` [RFC][PATCH 2/6] pagewalk: only split huge pages when necessary Dave Hansen
2011-02-01 10:04 ` Johannes Weiner
2011-02-01 15:03 ` Dave Hansen
2011-02-03 21:22 ` David Rientjes
2011-02-03 21:33 ` Dave Hansen
2011-02-03 21:46 ` David Rientjes
2011-02-04 17:19 ` Dave Hansen
2011-02-04 21:10 ` Andrea Arcangeli
2011-02-01 0:34 ` [RFC][PATCH 3/6] break out smaps_pte_entry() from smaps_pte_range() Dave Hansen
2011-02-01 10:08 ` Johannes Weiner
2011-02-03 21:22 ` David Rientjes
2011-02-03 21:40 ` Dave Hansen
2011-02-01 0:34 ` [RFC][PATCH 4/6] pass pte size argument in to smaps_pte_entry() Dave Hansen
2011-02-01 10:09 ` Johannes Weiner
2011-02-03 21:22 ` David Rientjes
2011-02-01 0:34 ` [RFC][PATCH 5/6] teach smaps_pte_range() about THP pmds Dave Hansen
2011-02-01 10:11 ` Johannes Weiner
2011-02-01 15:02 ` Dave Hansen
2011-02-01 16:09 ` Andrea Arcangeli
2011-02-03 21:22 ` David Rientjes
2011-02-03 21:34 ` Dave Hansen
2011-02-01 0:34 ` [RFC][PATCH 6/6] have smaps show transparent huge pages Dave Hansen
2011-02-01 10:12 ` Johannes Weiner
2011-02-03 21:22 ` David Rientjes
2011-02-01 15:38 ` [RFC][PATCH 0/6] more detailed per-process transparent hugepage statistics Andrea Arcangeli
2011-02-01 17:15 ` Dave Hansen [this message]
2011-02-01 20:39 ` Andrea Arcangeli
2011-02-01 20:56 ` Dave Hansen
2011-02-02 0:07 ` Andrea Arcangeli
2011-02-08 17:54 ` Dave Hansen
2011-02-08 18:17 ` Andrea Arcangeli
2011-02-03 21:54 ` David Rientjes
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=1296580547.27022.3370.camel@nimitz \
--to=dave@linux.vnet.ibm.com \
--cc=aarcange@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mjwolf@us.ibm.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).