Changelog: v3: * Dropped the zsmalloc patches from the set, except the promotion patch which has be converted to a rename patch (vs full diff). The dropped patches have been Acked and are going into Greg's staging tree soon. * Separated [PATCHv2 7/9] into two patches since it makes changes for two different reasons (Minchan) * Moved ZSWAP_MAX_OUTSTANDING_FLUSHES near the top in zswap.c (Rik) * Rebase to v3.8-rc5. linux-next is a little volatile with the swapper_space per type changes which will effect this patchset. * TODO: Move some stats from debugfs to sysfs. Which ones? (Rik)
v2: * Rename zswap_fs_* functions to zswap_frontswap_* to avoid confusion with "filesystem" * Add comment about what the tree lock protects * Remove "#if 0" code (should have been done before) * Break out changes to existing swap code into separate patch * Fix blank line EOF warning on documentation file * Rebase to next-20130107 Zswap Overview: Zswap is a lightweight compressed cache for swap pages. It takes pages that are in the process of being swapped out and attempts to compress them into a dynamically allocated RAM-based memory pool. If this process is successful, the writeback to the swap device is deferred and, in many cases, avoided completely. This results in a significant I/O reduction and performance gains for systems that are swapping. The results of a kernel building benchmark indicate a runtime reduction of 53% and an I/O reduction 76% with zswap vs normal swapping with a kernel build under heavy memory pressure (see Performance section for more). Some addition performance metrics regarding the performance improvements and I/O reductions that can be achieved using zswap as measured by SPECjbb are provided here: http://ibm.co/VCgHvM These results include runs on x86 and new results on Power7+ with hardware compression acceleration. Of particular note is that zswap is able to evict pages from the compressed cache, on an LRU basis, to the backing swap device when the compressed pool reaches it size limit or the pool is unable to obtain additional pages from the buddy allocator. This eviction functionality had been identified as a requirement in prior community discussions. Patchset Structure: 1: add atomic_t get/set to debugfs 2: promote zsmalloc to /lib 3,4: changes to existing swap code for zswap 5,6: add zswap and documentation Rationale: Zswap provides compressed swap caching that basically trades CPU cycles for reduced swap I/O. This trade-off can result in a significant performance improvement as reads to/writes from to the compressed cache almost always faster that reading from a swap device which incurs the latency of an asynchronous block I/O read. Some potential benefits: * Desktop/laptop users with limited RAM capacities can mitigate the performance impact of swapping. * Overcommitted guests that share a common I/O resource can dramatically reduce their swap I/O pressure, avoiding heavy handed I/O throttling by the hypervisor. This allows more work to get done with less impact to the guest workload and guests sharing the I/O subsystem * Users with SSDs as swap devices can extend the life of the device by drastically reducing life-shortening writes. Compressed swap is also provided in zcache, along with page cache compression and RAM clustering through RAMSter. Zswap seeks to deliver the benefit of swap compression to users in a discrete function. This design decision is akin to Unix design philosophy of doing one thing well, it leaves file cache compression and other features for separate code. Design: Zswap receives pages for compression through the Frontswap API and is able to evict pages from its own compressed pool on an LRU basis and write them back to the backing swap device in the case that the compressed pool is full or unable to secure additional pages from the buddy allocator. Zswap makes use of zsmalloc for the managing the compressed memory pool. This is because zsmalloc is specifically designed to minimize fragmentation on large (> PAGE_SIZE/2) allocation sizes. Each allocation in zsmalloc is not directly accessible by address. Rather, a handle is return by the allocation routine and that handle must be mapped before being accessed. The compressed memory pool grows on demand and shrinks as compressed pages are freed. The pool is not preallocated. When a swap page is passed from frontswap to zswap, zswap maintains a mapping of the swap entry, a combination of the swap type and swap offset, to the zsmalloc handle that references that compressed swap page. This mapping is achieved with a red-black tree per swap type. The swap offset is the search key for the tree nodes. Zswap seeks to be simple in its policies. Sysfs attributes allow for two user controlled policies: * max_compression_ratio - Maximum compression ratio, as as percentage, for an acceptable compressed page. Any page that does not compress by at least this ratio will be rejected. * max_pool_percent - The maximum percentage of memory that the compressed pool can occupy. To enabled zswap, the "enabled" attribute must be set to 1 at boot time. Zswap allows the compressor to be selected at kernel boot time by setting the “compressor” attribute. The default compressor is lzo. A debugfs interface is provided for various statistic about pool size, number of pages stored, and various counters for the reasons pages are rejected. Performance, Kernel Building: Setup ======== Gentoo w/ kernel v3.7-rc7 Quad-core i5-2500 @ 3.3GHz 512MB DDR3 1600MHz (limited with mem=512m on boot) Filesystem and swap on 80GB HDD (about 58MB/s with hdparm -t) majflt are major page faults reported by the time command pswpin/out is the delta of pswpin/out from /proc/vmstat before and after the make -jN Summary ======== * Zswap reduces I/O and improves performance at all swap pressure levels. * Under heavy swaping at 24 threads, zswap reduced I/O by 76%, saving over 1.5GB of I/O, and cut runtime in half. Details ======== I/O (in pages) base zswap change change N pswpin pswpout majflt I/O sum pswpin pswpout majflt I/O sum %I/O MB 8 1 335 291 627 0 0 249 249 -60% 1 12 3688 14315 5290 23293 123 860 5954 6937 -70% 64 16 12711 46179 16803 75693 2936 7390 46092 56418 -25% 75 20 42178 133781 49898 225857 9460 28382 92951 130793 -42% 371 24 96079 357280 105242 558601 7719 18484 109309 135512 -76% 1653 Runtime (in seconds) N base zswap %change 8 107 107 0% 12 128 110 -14% 16 191 179 -6% 20 371 240 -35% 24 570 267 -53% %CPU utilization (out of 400% on 4 cpus) N base zswap %change 8 317 319 1% 12 267 311 16% 16 179 191 7% 20 94 143 52% 24 60 128 113% Seth Jennings (6): debugfs: add get/set for atomic types zsmalloc: promote to lib/ mm: break up swap_writepage() for frontswap backends mm: allow for outstanding swap writeback accounting zswap: add to mm/ zswap: add documentation Documentation/vm/zswap.txt | 73 ++ drivers/staging/Kconfig | 2 - drivers/staging/Makefile | 1 - drivers/staging/zcache/zcache-main.c | 3 +- drivers/staging/zram/zram_drv.h | 3 +- drivers/staging/zsmalloc/Kconfig | 10 - drivers/staging/zsmalloc/Makefile | 3 - fs/debugfs/file.c | 42 + include/linux/debugfs.h | 2 + include/linux/swap.h | 4 + .../staging/zsmalloc => include/linux}/zsmalloc.h | 0 lib/Kconfig | 18 + lib/Makefile | 1 + .../zsmalloc/zsmalloc-main.c => lib/zsmalloc.c | 3 +- mm/Kconfig | 15 + mm/Makefile | 1 + mm/page_io.c | 22 +- mm/swap_state.c | 2 +- mm/zswap.c | 1073 ++++++++++++++++++++ 19 files changed, 1250 insertions(+), 28 deletions(-) create mode 100644 Documentation/vm/zswap.txt delete mode 100644 drivers/staging/zsmalloc/Kconfig delete mode 100644 drivers/staging/zsmalloc/Makefile rename {drivers/staging/zsmalloc => include/linux}/zsmalloc.h (100%) rename drivers/staging/zsmalloc/zsmalloc-main.c => lib/zsmalloc.c (99%) create mode 100644 mm/zswap.c -- 1.7.9.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
