Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755496Ab3H3NSJ (ORCPT ); Fri, 30 Aug 2013 09:18:09 -0400 Received: from e9.ny.us.ibm.com ([32.97.182.139]:52623 "EHLO e9.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752374Ab3H3NSG (ORCPT ); Fri, 30 Aug 2013 09:18:06 -0400 From: "Srivatsa S. Bhat" Subject: [RESEND RFC PATCH v3 00/35] mm: Memory Power Management To: akpm@linux-foundation.org, mgorman@suse.de, hannes@cmpxchg.org, tony.luck@intel.com, matthew.garrett@nebula.com, dave@sr71.net, riel@redhat.com, arjan@linux.intel.com, srinivas.pandruvada@linux.intel.com, willy@linux.intel.com, kamezawa.hiroyu@jp.fujitsu.com, lenb@kernel.org, rjw@sisk.pl Cc: gargankita@gmail.com, paulmck@linux.vnet.ibm.com, svaidy@linux.vnet.ibm.com, andi@firstfloor.org, isimatu.yasuaki@jp.fujitsu.com, santosh.shilimkar@ti.com, kosaki.motohiro@gmail.com, srivatsa.bhat@linux.vnet.ibm.com, linux-pm@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Date: Fri, 30 Aug 2013 18:43:54 +0530 Message-ID: <20130830131221.4947.99764.stgit@srivatsabhat.in.ibm.com> User-Agent: StGIT/0.14.3 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13083013-7182-0000-0000-000008410167 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 14887 Lines: 314 [ Resending, since some of the patches didn't go through successfully the last time around. ] Overview of Memory Power Management and its implications to the Linux MM ======================================================================== Today, we are increasingly seeing computer systems sporting larger and larger amounts of RAM, in order to meet workload demands. However, memory consumes a significant amount of power, potentially upto more than a third of total system power on server systems[4]. So naturally, memory becomes the next big target for power management - on embedded systems and smartphones, and all the way upto large server systems. Power-management capabilities in modern memory hardware: ------------------------------------------------------- Modern memory hardware such as DDR3 support a number of power management capabilities - for instance, the memory controller can automatically put memory DIMMs/banks into content-preserving low-power states, if it detects that the *entire* memory DIMM/bank has not been referenced for a threshold amount of time, thus reducing the energy consumption of the memory hardware. We term these power-manageable chunks of memory as "Memory Regions". Exporting memory region info from the platform to the OS: -------------------------------------------------------- The OS needs to know about the granularity at which the hardware can perform automatic power-management of the memory banks (i.e., the address boundaries of the memory regions). On ARM platforms, the bootloader can be modified to pass on this info to the kernel via the device-tree. On x86 platforms, the new ACPI 5.0 spec has added support for exporting the power-management capabilities of the memory hardware to the OS in a standard way[5][6]. Estimate of power-savings from power-aware Linux MM: --------------------------------------------------- Once the firmware/bootloader exports the required info to the OS, it is upto the kernel's MM subsystem to make the best use of these capabilities and manage memory power-efficiently. It had been demonstrated on a Samsung Exynos board (with 2 GB RAM) that upto 6 percent of total system power can be saved by making the Linux kernel MM subsystem power-aware[3]. (More savings can be expected on systems with larger amounts of memory, and perhaps improved further using better MM designs). Role of the Linux MM in enhancing memory power savings: ------------------------------------------------------ Often, this simply translates to having the Linux MM understand the granularity at which RAM modules can be power-managed, and keeping the memory allocations and references consolidated to a minimum no. of these power-manageable "memory regions". The memory hardware has the intelligence to automatically transition memory banks that haven't been referenced for a threshold amount of time, to low-power content-preserving states. And they can also perform OS-cooperative power-off of unused (unallocated) memory regions. So the onus is on the Linux VM to become power-aware and shape the allocations and influence the references in such a way that it helps conserve memory power. This involves consolidating the allocations/references at the right address boundaries, keeping the memory-region granularity in mind. So we can summarize the goals for the Linux MM as follows: o Consolidate memory allocations and/or references such that they are not spread across the entire memory address space, because the area of memory that is not being referenced can reside in low power state. o Support light-weight targeted memory compaction/reclaim, to evacuate lightly-filled memory regions. This helps avoid memory references to those regions, thereby allowing them to reside in low power states. Assumptions and goals of this patchset: -------------------------------------- In this patchset, we don't handle the part of getting the region boundary info from the firmware/bootloader and populating it in the kernel data-structures. The aim of this patchset is to propose and brainstorm on a power-aware design of the Linux MM which can *use* the region boundary info to influence the MM at various places such as page allocation, reclamation/compaction etc, thereby contributing to memory power savings. So, in this patchset, we assume a simple model in which each 512MB chunk of memory can be independently power-managed, and hard-code this in the kernel. As mentioned, the focus of this patchset is not so much on how we get this info from the firmware or how exactly we handle a variety of configurations, but rather on discussing the power-savings/performance impact of the MM algorithms that *act* upon this info in order to save memory power. That said, its not very far-fetched to try this out with actual region boundary info to get the real power savings numbers. For example, on ARM platforms, we can make the bootloader export this info to the OS via device-tree and then run this patchset. (This was the method used to get the power-numbers in [3]). But even without doing that, we can very well evaluate the effectiveness of this patchset in contributing to power-savings, by analyzing the free page statistics per-memory-region; and we can observe the performance impact by running benchmarks - this is the approach currently used to evaluate this patchset. Brief overview of the design/approach used in this patchset: ----------------------------------------------------------- The strategy used in this patchset is to do page allocation in increasing order of memory regions (within a zone) and perform region-compaction in the reverse order, as illustrated below. ---------------------------- Increasing region number----------------------> Direction of allocation---> <---Direction of region-compaction We achieve this by making 3 major design changes to the Linux kernel memory manager, as outlined below. 1. Sorted-buddy design of buddy freelists: To allocate pages in increasing order of memory regions, we first capture the memory region boundaries in suitable zone-level data-structures, and modify the buddy allocator such that we maintain the buddy freelists in region-sorted-order. Thus, automatically page allocation occurs in the order of increasing memory regions. 2. Split-allocator design: Page-Allocator as front-end; Region-Allocator as back-end: Mixing up movable and unmovable pages can disrupt opportunities for consolidating allocations. In order to separate such pages at a memory-region granularity, a "Region-Allocator" is introduced which allocates entire memory regions. The Page-Allocator is then modified to get its memory from the Region-Allocator and hand out pages to requesting applications in page-sized chunks. This design is showing significant improvements in the effectiveness of this patchset in consolidating allocations to minimum no. of memory regions. 3. Targeted region compaction/evacuation: Over time, due to multiple alloc()s and free()s in random order, memory gets fragmented, which means the memory allocations will no longer be consolidated to a minimum no. of memory regions. In such cases we need a light-weight mechanism to opportunistically compact memory to evacuate lightly-filled memory regions, thereby enhancing the power-savings. Noting that CMA (Contiguous Memory Allocator) does targeted compaction to achieve its goals, the v2 of this patchset generalized the targeted compaction code and reused it to evacuate memory regions. [ I have temporarily dropped this feature in this version (v3) of the patchset, since it can benefit from some considerable changes. I'll revive it in the next version and integrate it with the split-allocator design. ] Experimental Results: ==================== I'll include the detailed results as a reply to this cover-letter, since it can benefit from a dedicated discussion, rather than squeezing it here itself. This patchset has been hosted in the below git tree. It applies cleanly on v3.11-rc7. git://github.com/srivatsabhat/linux.git mem-power-mgmt-v3 Changes in v3: ============= * The major change is the splitting of the memory allocator into a Page-Allocator front-end and a Region-Allocator back-end. This helps in keeping movable and unmovable allocations separated across region boundaries, thus improving the opportunities for consolidation of memory allocations to a minimum no. of regions. * A bunch of fixes all over, especially in the handling of freepage migratetypes and the buddy merging code. Changes in v2: ============= * Fixed a bug in the NUMA case. * Added a new optimized O(log n) sorting algorithm to speed up region-sorting of the buddy freelists (patch 9). The efficiency of this new algorithm and its design allows us to support large amounts of RAM quite easily. * Added light-weight targetted compaction/reclaim support for memory power management (patches 10-14). * Revamped the cover-letter to better explain the idea behind memory power management and this patchset. Some important TODOs: ==================== 1. Revive the targeted region-compaction/evacuation code and make it work well with the new Page-Allocator - Region-Allocator split design. 2. Add optimizations to improve the performance and reduce the overhead in the MM hot paths. 3. Add support for making this patchset work with sparsemem, THP, memcg etc. References: ---------- [1]. LWN article that explains the goals and the design of my Memory Power Management patchset: http://lwn.net/Articles/547439/ [2]. v2 of the "Sorted-buddy" patchset with support for targeted memory region compaction: http://lwn.net/Articles/546696/ LWN article describing this design: http://lwn.net/Articles/547439/ v1 of the patchset: http://thread.gmane.org/gmane.linux.power-management.general/28498 [3]. Estimate of potential power savings on Samsung exynos board http://article.gmane.org/gmane.linux.kernel.mm/65935 [4]. C. Lefurgy, K. Rajamani, F. Rawson, W. Felter, M. Kistler, and Tom Keller. Energy management for commercial servers. In IEEE Computer, pages 39–48, Dec 2003. Link: researcher.ibm.com/files/us-lefurgy/computer2003.pdf [5]. ACPI 5.0 and MPST support http://www.acpi.info/spec.htm Section 5.2.21 Memory Power State Table (MPST) [6]. Prototype implementation of parsing of ACPI 5.0 MPST tables, by Srinivas Pandruvada. https://lkml.org/lkml/2013/4/18/349 [7]. Review comments suggesting modifying the buddy allocator to be aware of memory regions: http://article.gmane.org/gmane.linux.power-management.general/24862 http://article.gmane.org/gmane.linux.power-management.general/25061 http://article.gmane.org/gmane.linux.kernel.mm/64689 [8]. Patch series that implemented the node-region-zone hierarchy design: http://lwn.net/Articles/445045/ http://thread.gmane.org/gmane.linux.kernel.mm/63840 Summary of the discussion on that patchset: http://article.gmane.org/gmane.linux.power-management.general/25061 Forward-port of that patchset to 3.7-rc3 (minimal x86 config) http://thread.gmane.org/gmane.linux.kernel.mm/89202 [9]. Disadvantages of having memory regions in the hierarchy between nodes and zones: http://article.gmane.org/gmane.linux.kernel.mm/63849 Srivatsa S. Bhat (35): mm: Restructure free-page stealing code and fix a bug mm: Fix the value of fallback_migratetype in alloc_extfrag tracepoint mm: Introduce memory regions data-structure to capture region boundaries within nodes mm: Initialize node memory regions during boot mm: Introduce and initialize zone memory regions mm: Add helpers to retrieve node region and zone region for a given page mm: Add data-structures to describe memory regions within the zones' freelists mm: Demarcate and maintain pageblocks in region-order in the zones' freelists mm: Track the freepage migratetype of pages accurately mm: Use the correct migratetype during buddy merging mm: Add an optimized version of del_from_freelist to keep page allocation fast bitops: Document the difference in indexing between fls() and __fls() mm: A new optimized O(log n) sorting algo to speed up buddy-sorting mm: Add support to accurately track per-memory-region allocation mm: Print memory region statistics to understand the buddy allocator behavior mm: Enable per-memory-region fragmentation stats in pagetypeinfo mm: Add aggressive bias to prefer lower regions during page allocation mm: Introduce a "Region Allocator" to manage entire memory regions mm: Add a mechanism to add pages to buddy freelists in bulk mm: Provide a mechanism to delete pages from buddy freelists in bulk mm: Provide a mechanism to release free memory to the region allocator mm: Provide a mechanism to request free memory from the region allocator mm: Maintain the counter for freepages in the region allocator mm: Propagate the sorted-buddy bias for picking free regions, to region allocator mm: Fix vmstat to also account for freepages in the region allocator mm: Drop some very expensive sorted-buddy related checks under DEBUG_PAGEALLOC mm: Connect Page Allocator(PA) to Region Allocator(RA); add PA => RA flow mm: Connect Page Allocator(PA) to Region Allocator(RA); add PA <= RA flow mm: Update the freepage migratetype of pages during region allocation mm: Provide a mechanism to check if a given page is in the region allocator mm: Add a way to request pages of a particular region from the region allocator mm: Modify move_freepages() to handle pages in the region allocator properly mm: Never change migratetypes of pageblocks during freepage stealing mm: Set pageblock migratetype when allocating regions from region allocator mm: Use a cache between page-allocator and region-allocator arch/x86/include/asm/bitops.h | 4 include/asm-generic/bitops/__fls.h | 5 include/linux/mm.h | 42 ++ include/linux/mmzone.h | 75 +++ include/trace/events/kmem.h | 10 mm/compaction.c | 2 mm/page_alloc.c | 935 +++++++++++++++++++++++++++++++++--- mm/vmstat.c | 130 +++++ 8 files changed, 1124 insertions(+), 79 deletions(-) Regards, Srivatsa S. Bhat IBM Linux Technology Center -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/