Hi Seth, On Tue, 2013-01-29 at 15:40 -0600, Seth Jennings wrote: > Sorry for the churn but just this set might be easier to review. > The code required for the flushing is in a separate patch now > as requested. > > Changelog: > > 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) > > NOTE: To build, read this: > http://lkml.org/lkml/2013/1/28/586 > > 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. How to get your benchmark? > > 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 (7): > debugfs: add get/set for atomic types > zsmalloc: promote to lib/ > zswap: add to mm/ > mm: break up swap_writepage() for frontswap backends > mm: allow for outstanding swap writeback accounting > zswap: add flushing support > 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 > _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/devel
