linux-kernel - Re: [PATCH 00/10] mm: Linux VM Infrastructure to support Memory Power Management

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAOJsxLHQP=-srK_uYYBsPb7+rUBnPZG7bzwtCd-rRaQa4ikUFg@mail.gmail.com>
Date:	Wed, 6 Jul 2011 11:45:41 +0300
From:	Pekka Enberg <penberg@...nel.org>
To:	Ankita Garg <ankita@...ibm.com>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linux-pm@...ts.linux-foundation.org,
	svaidy@...ux.vnet.ibm.com, thomas.abraham@...aro.org,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH 00/10] mm: Linux VM Infrastructure to support Memory Power Management

Hi Ankita,

[ I don't really know anything about memory power management but
  here's my two cents since you asked for it. ]

On Wed, Jun 29, 2011 at 4:00 PM, Ankita Garg <ankita@...ibm.com> wrote:
> I) Dynamic Power Transition
>
> The goal here is to ensure that as much as possible, on an idle system,
> the memory references do not get spread across the entire RAM, a problem
> similar to memory fragmentation. The proposed approach is as below:
>
> 1) One of the first things is to ensure that the memory allocations do
> not spill over to more number of regions. Thus the allocator needs to
> be aware of the address boundary of the different regions.

Why does the allocator need to know about address boundaries? Why
isn't it enough to make the page allocator and reclaim policies favor using
memory from lower addresses as aggressively as possible? That'd mean
we'd favor the first memory banks and could keep the remaining ones
powered off as much as possible.

IOW, why do we need to support scenarios such as this:

   bank 0     bank 1   bank 2    bank3
 | online  | offline | online  | offline |

instead of using memory compaction and possibly something like the
SLUB defragmentation patches to turn the memory map into this:

   bank 0     bank 1   bank 2   bank3
 | online  | online  | offline | offline |

> 2) At the time of allocation, before spilling over allocations to the
> next logical region, the allocator needs to make a best attempt to
> reclaim some memory from within the existing region itself first. The
> reclaim here needs to be in LRU order within the region.  However, if
> it is ascertained that the reclaim would take a lot of time, like there
> are quite a fe write-backs needed, then we can spill over to the next
> memory region (just like our NUMA node allocation policy now).

I think a much more important question is what happens _after_ we've
allocated and free'd tons of memory few times. AFAICT, memory
regions don't help with that kind of fragmentation that will eventually
happen anyway.

					Pekka
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/