Re: [PATCH 0/8] zcache: page cache compression support

CAI Qian
2010-07-23T17:41:43Z

----- caiqian@redhat.com wrote:

> ----- "Nitin Gupta" <ngupta@vflare.org> wrote:
>
> > Frequently accessed filesystem data is stored in memory to reduce
> > access to
> > (much) slower backing disks. Under memory pressure, these pages are
> > freed and
> > when needed again, they have to be read from disks again. When
> > combined working
> > set of all running application exceeds amount of physical RAM, we
> get
> > extereme
> > slowdown as reading a page from disk can take time in order of
> > milliseconds.
> >
> > Memory compression increases effective memory size and allows more
> > pages to
> > stay in RAM. Since de/compressing memory pages is several orders of
> > magnitude
> > faster than disk I/O, this can provide signifant performance gains
> for
> > many
> > workloads. Also, with multi-cores becoming common, benefits of
> reduced
> > disk I/O
> > should easily outweigh the problem of increased CPU usage.
> >
> > It is implemented as a "backend" for cleancache_ops [1] which
> > provides
> > callbacks for events such as when a page is to be removed from the
> > page cache
> > and when it is required again. We use them to implement a 'second
> > chance' cache
> > for these evicted page cache pages by compressing and storing them
> in
> > memory
> > itself.
> >
> > We only keep pages that compress to PAGE_SIZE/2 or less. Compressed
> > chunks are
> > stored using xvmalloc memory allocator which is already being used
> by
> > zram
> > driver for the same purpose. Zero-filled pages are checked and no
> > memory is
> > allocated for them.
> >
> > A separate "pool" is created for each mount instance for a
> > cleancache-aware
> > filesystem. Each incoming page is identified with <pool_id,
> inode_no,
> > index>
> > where inode_no identifies file within the filesystem corresponding
> to
> > pool_id
> > and index is offset of the page within this inode. Within a pool,
> > inodes are
> > maintained in an rb-tree and each of its nodes points to a separate
> > radix-tree
> > which maintains list of pages within that inode.
> >
> > While compression reduces disk I/O, it also reduces the space
> > available for
> > normal (uncompressed) page cache. This can result in more frequent
> > page cache
> > reclaim and thus higher CPU overhead. Thus, it's important to
> maintain
> > good hit
> > rate for compressed cache or increased CPU overhead can nullify any
> > other
> > benefits. This requires adaptive (compressed) cache resizing and
> page
> > replacement policies that can maintain optimal cache size and
> quickly
> > reclaim
> > unused compressed chunks. This work is yet to be done. However, in
> the
> > current
> > state, it allows manually resizing cache size using (per-pool)
> sysfs
> > node
> > 'memlimit' which in turn frees any excess pages *sigh* randomly.
> >
> > Finally, it uses percpu stats and compression buffers to allow
> better
> > performance on multi-cores. Still, there are known bottlenecks like
> a
> > single
> > xvmalloc mempool per zcache pool and few others. I will work on
> this
> > when I
> > start with profiling.
> >
> > * Performance numbers:
> > - Tested using iozone filesystem benchmark
> > - 4 CPUs, 1G RAM
> > - Read performance gain: ~2.5X
> > - Random read performance gain: ~3X
> > - In general, performance gains for every kind of I/O
> >
> > Test details with graphs can be found here:
> > http://code.google.com/p/compcache/wiki/zcacheIOzone
> >
> > If I can get some help with testing, it would be intersting to find
> > its
> > effect in more real-life workloads. In particular, I'm intersted in
> > finding
> > out its effect in KVM virtualization case where it can potentially
> > allow
> > running more number of VMs per-host for a given amount of RAM. With
> > zcache
> > enabled, VMs can be assigned much smaller amount of memory since
> host
> > can now
> > hold bulk of page-cache pages, allowing VMs to maintain similar
> level
> > of
> > performance while a greater number of them can be hosted.
> >
> > * How to test:
> > All patches are against 2.6.35-rc5:
> >
> > - First, apply all prerequisite patches here:
> > http://compcache.googlecode.com/hg/sub-projects/zcache_base_patches
> >
> > - Then apply this patch series; also uploaded here:
> > http://compcache.googlecode.com/hg/sub-projects/zcache_patches
> >
> >
> > Nitin Gupta (8):
> > Allow sharing xvmalloc for zram and zcache
> > Basic zcache functionality
> > Create sysfs nodes and export basic statistics
> > Shrink zcache based on memlimit
> > Eliminate zero-filled pages
> > Compress pages using LZO
> > Use xvmalloc to store compressed chunks
> > Document sysfs entries
> >
> > Documentation/ABI/testing/sysfs-kernel-mm-zcache | 53 +
> > drivers/staging/Makefile | 2 +
> > drivers/staging/zram/Kconfig | 22 +
> > drivers/staging/zram/Makefile | 5 +-
> > drivers/staging/zram/xvmalloc.c | 8 +
> > drivers/staging/zram/zcache_drv.c | 1312
> > ++++++++++++++++++++++
> > drivers/staging/zram/zcache_drv.h | 90 ++
> > 7 files changed, 1491 insertions(+), 1 deletions(-)
> > create mode 100644
> Documentation/ABI/testing/sysfs-kernel-mm-zcache
> > create mode 100644 drivers/staging/zram/zcache_drv.c
> > create mode 100644 drivers/staging/zram/zcache_drv.h
> By tested those patches on the top of the linus tree at this commit
> d0c6f6258478e1dba532bf7c28e2cd6e1047d3a4, the OOM was trigger even
> though there looked like still lots of swap.
>
> # free -m
> total used free shared buffers
> cached
> Mem: 852 379 473 0 3
> 15
> -/+ buffers/cache: 359 492
> Swap: 2015 14 2001
>
> # ./usemem 1024
> 0: Mallocing 32 megabytes
> 1: Mallocing 32 megabytes
> 2: Mallocing 32 megabytes
> 3: Mallocing 32 megabytes
> 4: Mallocing 32 megabytes
> 5: Mallocing 32 megabytes
> 6: Mallocing 32 megabytes
> 7: Mallocing 32 megabytes
> 8: Mallocing 32 megabytes
> 9: Mallocing 32 megabytes
> 10: Mallocing 32 megabytes
> 11: Mallocing 32 megabytes
> 12: Mallocing 32 megabytes
> 13: Mallocing 32 megabytes
> 14: Mallocing 32 megabytes
> 15: Mallocing 32 megabytes
> Connection to 192.168.122.193 closed.
>
> usemem invoked oom-killer: gfp_mask=0x280da, order=0, oom_adj=0
> usemem cpuset=/ mems_allowed=0
> Pid: 1829, comm: usemem Not tainted 2.6.35-rc5+ #5
> Call Trace:
> [<ffffffff814e10cb>] ? _raw_spin_unlock+0x2b/0x40
> [<ffffffff81108520>] dump_header+0x70/0x190
> [<ffffffff811086c1>] oom_kill_process+0x81/0x180
> [<ffffffff81108c08>] __out_of_memory+0x58/0xd0
> [<ffffffff81108ddc>] ? out_of_memory+0x15c/0x1f0
> [<ffffffff81108d8f>] out_of_memory+0x10f/0x1f0
> [<ffffffff8110cc7f>] __alloc_pages_nodemask+0x7af/0x7c0
> [<ffffffff81140a69>] alloc_page_vma+0x89/0x140
> [<ffffffff81125f76>] handle_mm_fault+0x6d6/0x990
> [<ffffffff814e10cb>] ? _raw_spin_unlock+0x2b/0x40
> [<ffffffff81121afd>] ? follow_page+0x19d/0x350
> [<ffffffff8112639c>] __get_user_pages+0x16c/0x480
> [<ffffffff810127c9>] ? sched_clock+0x9/0x10
> [<ffffffff811276ef>] __mlock_vma_pages_range+0xef/0x1f0
> [<ffffffff81127f01>] mlock_vma_pages_range+0x91/0xa0
> [<ffffffff8112ad57>] mmap_region+0x307/0x5b0
> [<ffffffff8112b354>] do_mmap_pgoff+0x354/0x3a0
> [<ffffffff8112b3fc>] ? sys_mmap_pgoff+0x5c/0x200
> [<ffffffff8112b41a>] sys_mmap_pgoff+0x7a/0x200
> [<ffffffff814e02f2>] ? trace_hardirqs_on_thunk+0x3a/0x3f
> [<ffffffff8100fa09>] sys_mmap+0x29/0x30
> [<ffffffff8100b032>] system_call_fastpath+0x16/0x1b
> Mem-Info:
> Node 0 DMA per-cpu:
> CPU 0: hi: 0, btch: 1 usd: 0
> CPU 1: hi: 0, btch: 1 usd: 0
> Node 0 DMA32 per-cpu:
> CPU 0: hi: 186, btch: 31 usd: 140
> CPU 1: hi: 186, btch: 31 usd: 47
> active_anon:128 inactive_anon:140 isolated_anon:0
> active_file:0 inactive_file:9 isolated_file:0
> unevictable:126855 dirty:0 writeback:125 unstable:0
> free:1996 slab_reclaimable:4445 slab_unreclaimable:23646
> mapped:923 shmem:7 pagetables:778 bounce:0
> Node 0 DMA free:4032kB min:60kB low:72kB high:88kB active_anon:0kB
> inactive_anon:0kB active_file:0kB inactive_file:0kB
> unevictable:11896kB isolated(anon):0kB isolated(file):0kB
> present:15756kB mlocked:11896kB dirty:0kB writeback:0kB mapped:0kB
> shmem:0kB slab_reclaimable:0kB slab_unreclaimable:0kB kernel_stack:0kB
> pagetables:24kB unstable:0kB bounce:0kB writeback_tmp:0kB
> pages_scanned:0 all_unreclaimable? yes
> lowmem_reserve[]: 0 994 994 994
> Node 0 DMA32 free:3952kB min:4000kB low:5000kB high:6000kB
> active_anon:512kB inactive_anon:560kB active_file:0kB
> inactive_file:36kB unevictable:495524kB isolated(anon):0kB
> isolated(file):0kB present:1018060kB mlocked:495524kB dirty:0kB
> writeback:500kB mapped:3692kB shmem:28kB slab_reclaimable:17780kB
> slab_unreclaimable:94584kB kernel_stack:1296kB pagetables:3088kB
> unstable:0kB bounce:0kB writeback_tmp:0kB pages_scanned:1726
> all_unreclaimable? yes
> lowmem_reserve[]: 0 0 0 0
> Node 0 DMA: 0*4kB 2*8kB 1*16kB 1*32kB 2*64kB 2*128kB 2*256kB 0*512kB
> 1*1024kB 1*2048kB 0*4096kB = 4032kB
> Node 0 DMA32: 476*4kB 0*8kB 0*16kB 0*32kB 0*64kB 0*128kB 0*256kB
> 0*512kB 0*1024kB 1*2048kB 0*4096kB = 3952kB
> 1146 total pagecache pages
> 215 pages in swap cache
> Swap cache stats: add 19633, delete 19418, find 941/1333
> Free swap = 2051080kB
> Total swap = 2064380kB
> 262138 pages RAM
> 43914 pages reserved
> 4832 pages shared
> 155665 pages non-shared
> Out of memory: kill process 1727 (console-kit-dae) score 1027939 or a
> child
> Killed process 1727 (console-kit-dae) vsz:4111756kB, anon-rss:0kB,
> file-rss:600kB
> console-kit-dae invoked oom-killer: gfp_mask=0xd0, order=0, oom_adj=0
> console-kit-dae cpuset=/ mems_allowed=0
> Pid: 1752, comm: console-kit-dae Not tainted 2.6.35-rc5+ #5
> Call Trace:
> [<ffffffff814e10cb>] ? _raw_spin_unlock+0x2b/0x40
> [<ffffffff81108520>] dump_header+0x70/0x190
> [<ffffffff811086c1>] oom_kill_process+0x81/0x180
> [<ffffffff81108c08>] __out_of_memory+0x58/0xd0
> [<ffffffff81108ddc>] ? out_of_memory+0x15c/0x1f0
> [<ffffffff81108d8f>] out_of_memory+0x10f/0x1f0
> [<ffffffff8110cc7f>] __alloc_pages_nodemask+0x7af/0x7c0
> [<ffffffff8114522e>] kmem_getpages+0x6e/0x180
> [<ffffffff81147d79>] fallback_alloc+0x1c9/0x2b0
> [<ffffffff81147602>] ? cache_grow+0x4b2/0x520
> [<ffffffff81147a5b>] ____cache_alloc_node+0xab/0x200
> [<ffffffff810d55d5>] ? taskstats_exit+0x305/0x3b0
> [<ffffffff8114862b>] kmem_cache_alloc+0x1fb/0x290
> [<ffffffff810d55d5>] taskstats_exit+0x305/0x3b0
> [<ffffffff81063a4b>] do_exit+0x12b/0x890
> [<ffffffff810924fd>] ? trace_hardirqs_off+0xd/0x10
> [<ffffffff8108641f>] ? cpu_clock+0x6f/0x80
> [<ffffffff81095cbd>] ? lock_release_holdtime+0x3d/0x190
> [<ffffffff814e1010>] ? _raw_spin_unlock_irq+0x30/0x40
> [<ffffffff8106420e>] do_group_exit+0x5e/0xd0
> [<ffffffff81075b54>] get_signal_to_deliver+0x2d4/0x490
> [<ffffffff811ea6ad>] ? inode_has_perm+0x7d/0xf0
> [<ffffffff8100a2e5>] do_signal+0x75/0x7b0
> [<ffffffff81169d2d>] ? vfs_ioctl+0x3d/0xf0
> [<ffffffff8116a394>] ? do_vfs_ioctl+0x84/0x570
> [<ffffffff8100aa85>] do_notify_resume+0x65/0x80
> [<ffffffff814e02f2>] ? trace_hardirqs_on_thunk+0x3a/0x3f
> [<ffffffff8100b381>] int_signal+0x12/0x17
> Mem-Info:
> Node 0 DMA per-cpu:
> CPU 0: hi: 0, btch: 1 usd: 0
> CPU 1: hi: 0, btch: 1 usd: 0
> Node 0 DMA32 per-cpu:
> CPU 0: hi: 186, btch: 31 usd: 151
> CPU 1: hi: 186, btch: 31 usd: 61
> active_anon:128 inactive_anon:165 isolated_anon:0
> active_file:0 inactive_file:9 isolated_file:0
> unevictable:126855 dirty:0 writeback:25 unstable:0
> free:1965 slab_reclaimable:4445 slab_unreclaimable:23646
> mapped:923 shmem:7 pagetables:778 bounce:0
> Node 0 DMA free:4032kB min:60kB low:72kB high:88kB active_anon:0kB
> inactive_anon:0kB active_file:0kB inactive_file:0kB
> unevictable:11896kB isolated(anon):0kB isolated(file):0kB
> present:15756kB mlocked:11896kB dirty:0kB writeback:0kB mapped:0kB
> shmem:0kB slab_reclaimable:0kB slab_unreclaimable:0kB kernel_stack:0kB
> pagetables:24kB unstable:0kB bounce:0kB writeback_tmp:0kB
> pages_scanned:0 all_unreclaimable? yes
> lowmem_reserve[]: 0 994 994 994
> Node 0 DMA32 free:3828kB min:4000kB low:5000kB high:6000kB
> active_anon:512kB inactive_anon:660kB active_file:0kB
> inactive_file:36kB unevictable:495524kB isolated(anon):0kB
> isolated(file):0kB present:1018060kB mlocked:495524kB dirty:0kB
> writeback:100kB mapped:3692kB shmem:28kB slab_reclaimable:17780kB
> slab_unreclaimable:94584kB kernel_stack:1296kB pagetables:3088kB
> unstable:0kB bounce:0kB writeback_tmp:0kB pages_scanned:1726
> all_unreclaimable? yes
> lowmem_reserve[]: 0 0 0 0
> Node 0 DMA: 0*4kB 2*8kB 1*16kB 1*32kB 2*64kB 2*128kB 2*256kB 0*512kB
> 1*1024kB 1*2048kB 0*4096kB = 4032kB
> Node 0 DMA32: 445*4kB 0*8kB 0*16kB 0*32kB 0*64kB 0*128kB 0*256kB
> 0*512kB 0*1024kB 1*2048kB 0*4096kB = 3828kB
> 1146 total pagecache pages
> 230 pages in swap cache
> Swap cache stats: add 19649, delete 19419, find 942/1336
> Free swap = 2051084kB
> Total swap = 2064380kB
> 262138 pages RAM
> 43914 pages reserved
> 4818 pages shared
> 155685 pages non-shared
> Out of memory: kill process 1806 (sshd) score 9474 or a child
> Killed process 1810 (bash) vsz:108384kB, anon-rss:0kB, file-rss:656kB
> console-kit-dae invoked oom-killer: gfp_mask=0xd0, order=0, oom_adj=0
> console-kit-dae cpuset=/ mems_allowed=0
> Pid: 1752, comm: console-kit-dae Not tainted 2.6.35-rc5+ #5
> Call Trace:
> [<ffffffff814e10cb>] ? _raw_spin_unlock+0x2b/0x40
> [<ffffffff81108520>] dump_header+0x70/0x190
> [<ffffffff811086c1>] oom_kill_process+0x81/0x180
> [<ffffffff81108c08>] __out_of_memory+0x58/0xd0
> [<ffffffff81108ddc>] ? out_of_memory+0x15c/0x1f0
> [<ffffffff81108d8f>] out_of_memory+0x10f/0x1f0
> [<ffffffff8110cc7f>] __alloc_pages_nodemask+0x7af/0x7c0
> [<ffffffff8114522e>] kmem_getpages+0x6e/0x180
> [<ffffffff81147d79>] fallback_alloc+0x1c9/0x2b0
> [<ffffffff81147602>] ? cache_grow+0x4b2/0x520
> [<ffffffff81147a5b>] ____cache_alloc_node+0xab/0x200
> [<ffffffff810d55d5>] ? taskstats_exit+0x305/0x3b0
> [<ffffffff8114862b>] kmem_cache_alloc+0x1fb/0x290
> [<ffffffff810d55d5>] taskstats_exit+0x305/0x3b0
> [<ffffffff81063a4b>] do_exit+0x12b/0x890
> [<ffffffff810924fd>] ? trace_hardirqs_off+0xd/0x10
> [<ffffffff8108641f>] ? cpu_clock+0x6f/0x80
> [<ffffffff81095cbd>] ? lock_release_holdtime+0x3d/0x190
> [<ffffffff814e1010>] ? _raw_spin_unlock_irq+0x30/0x40
> [<ffffffff8106420e>] do_group_exit+0x5e/0xd0
> [<ffffffff81075b54>] get_signal_to_deliver+0x2d4/0x490
> [<ffffffff811ea6ad>] ? inode_has_perm+0x7d/0xf0
> [<ffffffff8100a2e5>] do_signal+0x75/0x7b0
> [<ffffffff81169d2d>] ? vfs_ioctl+0x3d/0xf0
> [<ffffffff8116a394>] ? do_vfs_ioctl+0x84/0x570
> [<ffffffff8100aa85>] do_notify_resume+0x65/0x80
> [<ffffffff814e02f2>] ? trace_hardirqs_on_thunk+0x3a/0x3f
> [<ffffffff8100b381>] int_signal+0x12/0x17
> Mem-Info:
> Node 0 DMA per-cpu:
> CPU 0: hi: 0, btch: 1 usd: 0
> CPU 1: hi: 0, btch: 1 usd: 0
> Node 0 DMA32 per-cpu:
> CPU 0: hi: 186, btch: 31 usd: 119
> CPU 1: hi: 186, btch: 31 usd: 73
> active_anon:50 inactive_anon:175 isolated_anon:0
> active_file:0 inactive_file:9 isolated_file:0
> unevictable:126855 dirty:0 writeback:25 unstable:0
> free:1996 slab_reclaimable:4445 slab_unreclaimable:23663
> mapped:923 shmem:7 pagetables:778 bounce:0
> Node 0 DMA free:4032kB min:60kB low:72kB high:88kB active_anon:0kB
> inactive_anon:0kB active_file:0kB inactive_file:0kB
> unevictable:11896kB isolated(anon):0kB isolated(file):0kB
> present:15756kB mlocked:11896kB dirty:0kB writeback:0kB mapped:0kB
> shmem:0kB slab_reclaimable:0kB slab_unreclaimable:0kB kernel_stack:0kB
> pagetables:24kB unstable:0kB bounce:0kB writeback_tmp:0kB
> pages_scanned:0 all_unreclaimable? yes
> lowmem_reserve[]: 0 994 994 994
> Node 0 DMA32 free:3952kB min:4000kB low:5000kB high:6000kB
> active_anon:200kB inactive_anon:700kB active_file:0kB
> inactive_file:36kB unevictable:495524kB isolated(anon):0kB
> isolated(file):0kB present:1018060kB mlocked:495524kB dirty:0kB
> writeback:100kB mapped:3692kB shmem:28kB slab_reclaimable:17780kB
> slab_unreclaimable:94652kB kernel_stack:1296kB pagetables:3088kB
> unstable:0kB bounce:0kB writeback_tmp:0kB pages_scanned:1536
> all_unreclaimable? yes
> lowmem_reserve[]: 0 0 0 0
> Node 0 DMA: 0*4kB 2*8kB 1*16kB 1*32kB 2*64kB 2*128kB 2*256kB 0*512kB
> 1*1024kB 1*2048kB 0*4096kB = 4032kB
> Node 0 DMA32: 470*4kB 3*8kB 0*16kB 0*32kB 0*64kB 0*128kB 0*256kB
> 0*512kB 0*1024kB 1*2048kB 0*4096kB = 3952kB
> 1146 total pagecache pages
> 221 pages in swap cache
> Swap cache stats: add 19848, delete 19627, find 970/1386
> Free swap = 2051428kB
> Total swap = 2064380kB
> 262138 pages RAM
> 43914 pages reserved
> 4669 pages shared
> 155659 pages non-shared
> Out of memory: kill process 1829 (usemem) score 8253 or a child
> Killed process 1829 (usemem) vsz:528224kB, anon-rss:502468kB,
> file-rss:376kB
>
> # cat usemem.c
> # cat usemem.c
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
> #include <sys/mman.h>
> #define CHUNKS 32
>
> int
> main(int argc, char *argv[])
> {
> mlockall(MCL_FUTURE);
>
> unsigned long mb;
> char *buf[CHUNKS];
> int i;
>
> if (argc < 2) {
> fprintf(stderr, "usage: usemem megabytes\n");
> exit(1);
> }
> mb = strtoul(argv[1], NULL, 0);
>
> for (i = 0; i < CHUNKS; i++) {
> fprintf(stderr, "%d: Mallocing %lu megabytes\n", i, mb/CHUNKS);
> buf[i] = (char *)malloc(mb/CHUNKS * 1024L * 1024L);
> if (!buf[i]) {
> fprintf(stderr, "malloc failure\n");
> exit(1);
> }
> }
>
> for (i = 0; i < CHUNKS; i++) {
> fprintf(stderr, "%d: Zeroing %lu megabytes at %p\n",
> i, mb/CHUNKS, buf[i]);
> memset(buf[i], 0, mb/CHUNKS * 1024L * 1024L);
> }
>
>
> exit(0);
> }
>
If this ever be relevant, this was tested inside the kvm guest. The host was a RHEL6 with THP enabled.