I wasn't looking to post this set again before the summit, but I messed up v8 and didn't include one of the fixes claimed in the changelog :-/ Namely "Fix load-during-writeback race; double lru add", which is a stability issue, as discovered by Heesub Shin (thanks for noticing!). There were also a couple of other fixups that didn't make it in that should have. I rebased to v3.9-rc6 while I was at it. zswap greatly improves performance and reduces swap I/O on systems in a state of VM thrashing (see details below). While this might not seem a likely scenario to those that have full control over the workloads that run on their systems, it can be very valuable to IaaS providers that have workloads running in customer managed guests with undersized RAM allocations. It is also beneficial in virtualized environments where the hypervisor either can't do or is not configured to do I/O QoS and heavy paging by a single guest can drastically increase I/O latency for all users of the shared I/O. zswap also helps the overcommitted guest as well by avoiding throttled swap I/O. I'll be attending the LSF/MM summit where there (hopefully) will be a discussion this patchset and memory compression in general. 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: 1-2: add zsmalloc and documentation 3: add atomic_t get/set to debugfs 4: add basic zswap functionality 4,5: changes to existing swap code for zswap 6,7: add zswap writeback support 8: add zswap 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. Changelog: v9: * Fix load-during-writeback race; double lru add (for real this time) * checkpatch and comment fixes * Fix __swap_writepage() return value check * Move check for max outstanding writebacks (dedup some code) * Rebase to v3.9-rc6 v8: * Fix load-during-writeback race; double lru add * checkpatch fixups * s/NOWAIT/ATOMIC for tree allocation (Dave) * Check __swap_writepage() for error before incr outstanding write count (Rob) * Convert pcpu compression buffer alloc from alloc_page() to kmalloc() (Dave) * Rebase to v3.9-rc5 v7: * Decrease zswap_stored_pages during tree cleanup (Joonsoo) * Move zswap_entry_cache_alloc() earlier during store (Joonsoo) * Move type field from struct zswap_entry to struct zswap_tree * Change to swapper_space array (-rc1 change) * s/reset_page_mapcount/page_mapcount_reset in zsmalloc (-rc1 change) * Rebase to v3.9-rc1 v6: * fix access-after-free regression introduced in v5 (rb_erase() outside the lock) * fix improper freeing of rbtree (Cody) * fix comment typo (Ric) * add comments about ZS_MM_WO usage and page mapping mode (Joonsoo) * don't use page->object (Joonsoo) * remove DEBUG (Joonsoo) * rebase to v3.8 v5: * zsmalloc patch converted from promotion to "new code" (for review only, see note in [1/8]) * promote zsmalloc to mm/ instead of /lib * add more documentation everywhere * convert USE_PGTABLE_MAPPING to kconfig option, thanks to Minchan * s/flush/writeback/ * #define pr_fmt() for formatting messages (Joe) * checkpatch fixups * lots of changes suggested Minchan v4: * Added Acks (Minchan) * Separated flushing functionality into standalone patch for easier review (Minchan) * fix comment on zswap enabled attribute (Minchan) * add TODO for dynamic mempool size (Minchan) * and check for NULL in zswap_free_page() (Minchan) * add missing zs_free() in error path (Minchan) * TODO: add comments for flushing/refcounting (Minchan) 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 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 (8): zsmalloc: add to mm/ zsmalloc: add documentation debugfs: add get/set for atomic types zswap: add to mm/ mm: break up swap_writepage() for frontswap backends mm: allow for outstanding swap writeback accounting zswap: add swap page writeback support zswap: add documentation Documentation/vm/zsmalloc.txt | 68 +++ Documentation/vm/zswap.txt | 82 +++ fs/debugfs/file.c | 42 ++ include/linux/debugfs.h | 2 + include/linux/swap.h | 4 + include/linux/zsmalloc.h | 56 ++ mm/Kconfig | 39 ++ mm/Makefile | 2 + mm/page_io.c | 22 +- mm/swap_state.c | 2 +- mm/zsmalloc.c | 1117 +++++++++++++++++++++++++++++++++++++++ mm/zswap.c | 1151 +++++++++++++++++++++++++++++++++++++++++ 12 files changed, 2581 insertions(+), 6 deletions(-) create mode 100644 Documentation/vm/zsmalloc.txt create mode 100644 Documentation/vm/zswap.txt create mode 100644 include/linux/zsmalloc.h create mode 100644 mm/zsmalloc.c create mode 100644 mm/zswap.c -- 1.8.2.1 _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/devel
