linux-kernel - Re: Transparent Hugepage Support #30

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Date:	Thu, 9 Sep 2010 16:16:30 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Andrea Arcangeli <aarcange@...hat.com>
Cc:	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Adam Litke <agl@...ibm.com>, Avi Kivity <avi@...hat.com>,
	Izik Eidus <ieidus@...hat.com>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Nick Piggin <npiggin@...e.de>, Rik van Riel <riel@...hat.com>,
	Mel Gorman <mel@....ul.ie>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Ingo Molnar <mingo@...e.hu>, Mike Travis <travis@....com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Chris Wright <chrisw@...s-sol.org>, bpicco@...hat.com,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Chris Mason <chris.mason@...cle.com>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: Transparent Hugepage Support #30

* Andrea Arcangeli <aarcange@...hat.com> [2010-09-01 21:08:59]:

> http://www.linux-kvm.org/wiki/images/9/9e/2010-forum-thp.pdf
> 
> http://git.kernel.org/?p=linux/kernel/git/andrea/aa.git;a=shortlog
> 
> first: git clone git://git.kernel.org/pub/scm/linux/kernel/git/andrea/aa.git
> or first: git clone --reference linux-2.6 git://git.kernel.org/pub/scm/linux/kernel/git/andrea/aa.git
> later: git fetch; git checkout -f origin/master
> 
> The tree is rebased and git pull won't work.
> 
> http://www.kernel.org/pub/linux/kernel/people/andrea/patches/v2.6/2.6.36-rc3/transparent_hugepage-30/
> http://www.kernel.org/pub/linux/kernel/people/andrea/patches/v2.6/2.6.36-rc3/transparent_hugepage-30.gz
> 
> Diff #29 -> #30:
> 
>  b/compaction-migration-warning               |   25 +++
> 
> Avoid MIGRATION config warning when COMPACTION is selected but numa
> and memhotplug aren't.
> 
>  do_swap_page-VM_FAULT_WRITE                  |   21 --
>  kvm-huge-spte-wrprotect                      |   48 ------
>  kvm-mmu-notifier-huge-spte                   |   29 ---
>  root_anon_vma-anon_vma_lock                  |  208 ---------------------------
>  root_anon_vma-avoid-ksm-hang                 |   30 ---
>  root_anon_vma-bugchecks                      |   37 ----
>  root_anon_vma-in_vma                         |   27 ---
>  root_anon_vma-ksm_refcount                   |  169 ---------------------
>  root_anon_vma-lock_root                      |  127 ----------------
>  root_anon_vma-memory-compaction              |   36 ----
>  root_anon_vma-mm_take_all_locks              |   81 ----------
>  root_anon_vma-oldest_root                    |   81 ----------
>  root_anon_vma-refcount                       |   29 ---
>  root_anon_vma-swapin                         |   91 -----------
>  root_anon_vma-use-root                       |   66 --------
>  root_anon_vma-vma_lock_anon_vma              |   94 ------------
> 
> merged upstream.
> 
>  b/memcg_compound                             |  166 ++++++++++-----------
>  b/memcg_compound_tail                        |   31 +---
>  b/memcg_consume_stock                        |   31 ++--
>  memcg_check_room                             |   88 -----------
>  memcg_oom                                    |   34 ----
> 
> These had heavy rejects, the last two patches and other bits got
> removed. memcg code is rewritten so fast it's hard to justify to keep
> up with it. It's simpler and less time consuming to fix it just once
> than over and over again. Likely memcg in this release isn't too
> stable with THP on (it'll definitely work fine if you disable THP at
> compile time or at boot time with the kernel parameter). Especially
> all get_css/put_css will have to be re-audited after these new
> changes. For now it builds just fine and the basics to support THP and
> to show the direction are in. Nevertheless I welcome patches to fix
> this up.
> 
> btw, memcg developers could already support THP inside memcg even if
> THP is not included yet without any sort of problem, so it's also

Could you elaborate by what you mean here?

> partly up to them to want to support THP in memcg, but it's also
> perfectly ok to catch up with memcg externally, but it'd be also nice
> to know when memcg reaches a milestone and so when it's time to
> re-audit it all for THP.
>

We try not to change too drastically, but several of the current
changes are fixes, we are currently contemplating some more changes to
support the I/O control. Some of the recent changes have been driven
by tracing. We will pay closer attention to THP changes, thanks for
bring your concern to our notice.

-- 
	Three Cheers,
	Balbir
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