98fad86293
12 Commits
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Matthew Ahrens
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e8b96c6007 |
Illumos #4045 write throttle & i/o scheduler performance work
4045 zfs write throttle & i/o scheduler performance work 1. The ZFS i/o scheduler (vdev_queue.c) now divides i/os into 5 classes: sync read, sync write, async read, async write, and scrub/resilver. The scheduler issues a number of concurrent i/os from each class to the device. Once a class has been selected, an i/o is selected from this class using either an elevator algorithem (async, scrub classes) or FIFO (sync classes). The number of concurrent async write i/os is tuned dynamically based on i/o load, to achieve good sync i/o latency when there is not a high load of writes, and good write throughput when there is. See the block comment in vdev_queue.c (reproduced below) for more details. 2. The write throttle (dsl_pool_tempreserve_space() and txg_constrain_throughput()) is rewritten to produce much more consistent delays when under constant load. The new write throttle is based on the amount of dirty data, rather than guesses about future performance of the system. When there is a lot of dirty data, each transaction (e.g. write() syscall) will be delayed by the same small amount. This eliminates the "brick wall of wait" that the old write throttle could hit, causing all transactions to wait several seconds until the next txg opens. One of the keys to the new write throttle is decrementing the amount of dirty data as i/o completes, rather than at the end of spa_sync(). Note that the write throttle is only applied once the i/o scheduler is issuing the maximum number of outstanding async writes. See the block comments in dsl_pool.c and above dmu_tx_delay() (reproduced below) for more details. This diff has several other effects, including: * the commonly-tuned global variable zfs_vdev_max_pending has been removed; use per-class zfs_vdev_*_max_active values or zfs_vdev_max_active instead. * the size of each txg (meaning the amount of dirty data written, and thus the time it takes to write out) is now controlled differently. There is no longer an explicit time goal; the primary determinant is amount of dirty data. Systems that are under light or medium load will now often see that a txg is always syncing, but the impact to performance (e.g. read latency) is minimal. Tune zfs_dirty_data_max and zfs_dirty_data_sync to control this. * zio_taskq_batch_pct = 75 -- Only use 75% of all CPUs for compression, checksum, etc. This improves latency by not allowing these CPU-intensive tasks to consume all CPU (on machines with at least 4 CPU's; the percentage is rounded up). --matt APPENDIX: problems with the current i/o scheduler The current ZFS i/o scheduler (vdev_queue.c) is deadline based. The problem with this is that if there are always i/os pending, then certain classes of i/os can see very long delays. For example, if there are always synchronous reads outstanding, then no async writes will be serviced until they become "past due". One symptom of this situation is that each pass of the txg sync takes at least several seconds (typically 3 seconds). If many i/os become "past due" (their deadline is in the past), then we must service all of these overdue i/os before any new i/os. This happens when we enqueue a batch of async writes for the txg sync, with deadlines 2.5 seconds in the future. If we can't complete all the i/os in 2.5 seconds (e.g. because there were always reads pending), then these i/os will become past due. Now we must service all the "async" writes (which could be hundreds of megabytes) before we service any reads, introducing considerable latency to synchronous i/os (reads or ZIL writes). Notes on porting to ZFS on Linux: - zio_t gained new members io_physdone and io_phys_children. Because object caches in the Linux port call the constructor only once at allocation time, objects may contain residual data when retrieved from the cache. Therefore zio_create() was updated to zero out the two new fields. - vdev_mirror_pending() relied on the depth of the per-vdev pending queue (vq->vq_pending_tree) to select the least-busy leaf vdev to read from. This tree has been replaced by vq->vq_active_tree which is now used for the same purpose. - vdev_queue_init() used the value of zfs_vdev_max_pending to determine the number of vdev I/O buffers to pre-allocate. That global no longer exists, so we instead use the sum of the *_max_active values for each of the five I/O classes described above. - The Illumos implementation of dmu_tx_delay() delays a transaction by sleeping in condition variable embedded in the thread (curthread->t_delay_cv). We do not have an equivalent CV to use in Linux, so this change replaced the delay logic with a wrapper called zfs_sleep_until(). This wrapper could be adopted upstream and in other downstream ports to abstract away operating system-specific delay logic. - These tunables are added as module parameters, and descriptions added to the zfs-module-parameters.5 man page. spa_asize_inflation zfs_deadman_synctime_ms zfs_vdev_max_active zfs_vdev_async_write_active_min_dirty_percent zfs_vdev_async_write_active_max_dirty_percent zfs_vdev_async_read_max_active zfs_vdev_async_read_min_active zfs_vdev_async_write_max_active zfs_vdev_async_write_min_active zfs_vdev_scrub_max_active zfs_vdev_scrub_min_active zfs_vdev_sync_read_max_active zfs_vdev_sync_read_min_active zfs_vdev_sync_write_max_active zfs_vdev_sync_write_min_active zfs_dirty_data_max_percent zfs_delay_min_dirty_percent zfs_dirty_data_max_max_percent zfs_dirty_data_max zfs_dirty_data_max_max zfs_dirty_data_sync zfs_delay_scale The latter four have type unsigned long, whereas they are uint64_t in Illumos. This accommodates Linux's module_param() supported types, but means they may overflow on 32-bit architectures. The values zfs_dirty_data_max and zfs_dirty_data_max_max are the most likely to overflow on 32-bit systems, since they express physical RAM sizes in bytes. In fact, Illumos initializes zfs_dirty_data_max_max to 2^32 which does overflow. To resolve that, this port instead initializes it in arc_init() to 25% of physical RAM, and adds the tunable zfs_dirty_data_max_max_percent to override that percentage. While this solution doesn't completely avoid the overflow issue, it should be a reasonable default for most systems, and the minority of affected systems can work around the issue by overriding the defaults. - Fixed reversed logic in comment above zfs_delay_scale declaration. - Clarified comments in vdev_queue.c regarding when per-queue minimums take effect. - Replaced dmu_tx_write_limit in the dmu_tx kstat file with dmu_tx_dirty_delay and dmu_tx_dirty_over_max. The first counts how many times a transaction has been delayed because the pool dirty data has exceeded zfs_delay_min_dirty_percent. The latter counts how many times the pool dirty data has exceeded zfs_dirty_data_max (which we expect to never happen). - The original patch would have regressed the bug fixed in zfsonlinux/zfs@c418410, which prevented users from setting the zfs_vdev_aggregation_limit tuning larger than SPA_MAXBLOCKSIZE. A similar fix is added to vdev_queue_aggregate(). - In vdev_queue_io_to_issue(), dynamically allocate 'zio_t search' on the heap instead of the stack. In Linux we can't afford such large structures on the stack. Reviewed by: George Wilson <george.wilson@delphix.com> Reviewed by: Adam Leventhal <ahl@delphix.com> Reviewed by: Christopher Siden <christopher.siden@delphix.com> Reviewed by: Ned Bass <bass6@llnl.gov> Reviewed by: Brendan Gregg <brendan.gregg@joyent.com> Approved by: Robert Mustacchi <rm@joyent.com> References: http://www.illumos.org/issues/4045 illumos/illumos-gate@69962b5647 Ported-by: Ned Bass <bass6@llnl.gov> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes #1913 |
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Matthew Ahrens
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498877baf5 |
Illumos #3112, #3113, #3114
3112 ztest does not honor ZFS_DEBUG 3113 ztest should use watchpoints to protect frozen arc bufs 3114 some leaked nvlists in zfsdev_ioctl Reviewed by: Adam Leventhal <ahl@delphix.com> Reviewed by: Matt Amdur <Matt.Amdur@delphix.com> Reviewed by: George Wilson <george.wilson@delphix.com> Reviewed by: Christopher Siden <chris.siden@delphix.com> Approved by: Eric Schrock <eric.schrock@delphix.com> References: https://www.illumos.org/issues/3112 https://www.illumos.org/issues/3113 https://www.illumos.org/issues/3114 illumos/illumos-gate@cd1c8b85eb The /proc/self/cmd watchpoint interface is specific to Solaris. Therefore, the #3113 implementation was reworked to use the more portable mprotect(2) system call. When the pages are watched they are marked read-only for protection. Any write to the protected address range immediately trigger a SIGSEGV. The pages are marked writable again when they are unwatched. Ported-by: Brian Behlendorf <behlendorf1@llnl.gov> Issue #1489 |
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Brian Behlendorf
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e0b0ca983d |
Add visibility in to cached dbufs
Currently there is no mechanism to inspect which dbufs are being cached by the system. There are some coarse counters in arcstats by they only give a rough idea of what's being cached. This patch aims to improve the current situation by adding a new dbufs kstat. When read this new kstat will walk all cached dbufs linked in to the dbuf_hash. For each dbuf it will dump detailed information about the buffer. It will also dump additional information about the referenced arc buffer and its related dnode. This provides a more complete view in to exactly what is being cached. With this generic infrastructure in place utilities can be written to post-process the data to understand exactly how the caching is working. For example, the data could be processed to show a list of all cached dnodes and how much space they're consuming. Or a similar list could be generated based on dnode type. Many other ways to interpret the data exist based on what kinds of questions you're trying to answer. Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Prakash Surya <surya1@llnl.gov> |
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Matthew Ahrens
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13fe019870 |
Illumos #3464
3464 zfs synctask code needs restructuring Reviewed by: Dan Kimmel <dan.kimmel@delphix.com> Reviewed by: Adam Leventhal <ahl@delphix.com> Reviewed by: George Wilson <george.wilson@delphix.com> Reviewed by: Christopher Siden <christopher.siden@delphix.com> Approved by: Garrett D'Amore <garrett@damore.org> References: https://www.illumos.org/issues/3464 illumos/illumos-gate@3b2aab1880 Ported-by: Tim Chase <tim@chase2k.com> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes #1495 |
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Saso Kiselkov
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3a17a7a99a |
Illumos #3137 L2ARC compression
3137 L2ARC compression Reviewed by: George Wilson <george.wilson@delphix.com> Reviewed by: Matthew Ahrens <mahrens@delphix.com> Approved by: Dan McDonald <danmcd@nexenta.com> References: illumos/illumos-gate@aad02571bc https://www.illumos.org/issues/3137 http://wiki.illumos.org/display/illumos/L2ARC+Compression Notes for Linux port: A l2arc_nocompress module option was added to prevent the compression of l2arc buffers regardless of how a dataset's compression property is set. This allows the legacy behavior to be preserved. Ported by: James H <james@kagisoft.co.uk> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes #1379 |
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Richard Yao
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3f4058cd15 |
Remove arc_data_buf_alloc()/arc_data_buf_free()
These functions are used in neither Illumos nor ZFSOnLinux. They appear to have been replaced by arc_buf_alloc()/arc_buf_free(), so lets remove them. Signed-off-by: Richard Yao <ryao@gentoo.org> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Issue #1614 |
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George Wilson
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294f68063b |
Illumos #3498 panic in arc_read()
3498 panic in arc_read(): !refcount_is_zero(&pbuf->b_hdr->b_refcnt) Reviewed by: Adam Leventhal <ahl@delphix.com> Reviewed by: Matthew Ahrens <mahrens@delphix.com> Approved by: Richard Lowe <richlowe@richlowe.net> References: illumos/illumos-gate@1b912ec710 https://www.illumos.org/issues/3498 Ported-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes #1249 |
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Matthew Ahrens
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df4474f92d |
Illumos #3805 arc shouldn't cache freed blocks
3805 arc shouldn't cache freed blocks Reviewed by: George Wilson <george.wilson@delphix.com> Reviewed by: Christopher Siden <christopher.siden@delphix.com> Reviewed by: Richard Elling <richard.elling@dey-sys.com> Reviewed by: Will Andrews <will@firepipe.net> Approved by: Dan McDonald <danmcd@nexenta.com> References: illumos/illumos-gate@6e6d5868f5 https://www.illumos.org/issues/3805 ZFS should proactively evict freed blocks from the cache. On dcenter, we saw that we were caching ~256GB of metadata, while the pool only had <4GB of metadata on disk. We were wasting about half the system's RAM (252GB) on blocks that have been freed. Even though these freed blocks will never be used again, and thus will eventually be evicted, this causes us to use memory inefficiently for 2 reasons: 1. A block that is freed has no chance of being accessed again, but will be kept in memory preferentially to a block that was accessed before it (and is thus older) but has not been freed and thus has at least some chance of being accessed again. 2. We partition the ARC into several buckets: user data that has been accessed only once (MRU) metadata that has been accessed only once (MRU) user data that has been accessed more than once (MFU) metadata that has been accessed more than once (MFU) The user data vs metadata split is somewhat arbitrary, and the primary control on how much memory is used to cache data vs metadata is to simply try to keep the proportion the same as it has been in the past (each bucket "evicts against" itself). The secondary control is to evict data before evicting metadata. Because of this bucketing, we may end up with one bucket mostly containing freed blocks that are very old, while another bucket has more recently accessed, still-allocated blocks. Data in the useful bucket (with still-allocated blocks) may be evicted in preference to data in the useless bucket (with old, freed blocks). On dcenter, we saw that the MFU metadata bucket was 230MB, while the MFU data bucket was 27GB and the MRU metadata bucket was 256GB. However, the vast majority of data in the MRU metadata bucket (256GB) was freed blocks, and thus useless. Meanwhile, the MFU metadata bucket (230MB) was constantly evicting useful blocks that will be soon needed. The problem of cache segmentation is a larger problem that needs more investigation. However, if we stop caching freed blocks, it should reduce the impact of this more fundamental issue. Ported-by: Richard Yao <ryao@cs.stonybrook.edu> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes #1503 |
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George Wilson
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1eb5bfa3dc |
Illumos #3145, #3212
3145 single-copy arc 3212 ztest: race condition between vdev_online() and spa_vdev_remove() Reviewed by: Matt Ahrens <matthew.ahrens@delphix.com> Reviewed by: Adam Leventhal <ahl@delphix.com> Reviewed by: Eric Schrock <eric.schrock@delphix.com> Reviewed by: Justin T. Gibbs <gibbs@scsiguy.com> Approved by: Eric Schrock <eric.schrock@delphix.com> References: illumos-gate/commit/9253d63df408bb48584e0b1abfcc24ef2472382e illumos changeset: 13840:97fd5cdf328a https://www.illumos.org/issues/3145 https://www.illumos.org/issues/3212 Ported-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes #989 Closes #1137 |
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Richard Yao
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7df05a4266 |
Fix zfs_write_limit_max integer size mismatch on 32-bit systems
Commit
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Brian Behlendorf
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ab26409db7 |
Linux 3.1 compat, super_block->s_shrink
The Linux 3.1 kernel has introduced the concept of per-filesystem shrinkers which are directly assoicated with a super block. Prior to this change there was one shared global shrinker. The zfs code relied on being able to call the global shrinker when the arc_meta_limit was exceeded. This would cause the VFS to drop references on a fraction of the dentries in the dcache. The ARC could then safely reclaim the memory used by these entries and honor the arc_meta_limit. Unfortunately, when per-filesystem shrinkers were added the old interfaces were made unavailable. This change adds support to use the new per-filesystem shrinker interface so we can continue to honor the arc_meta_limit. The major benefit of the new interface is that we can now target only the zfs filesystem for dentry and inode pruning. Thus we can minimize any impact on the caching of other filesystems. In the context of making this change several other important issues related to managing the ARC were addressed, they include: * The dnlc_reduce_cache() function which was called by the ARC to drop dentries for the Posix layer was replaced with a generic zfs_prune_t callback. The ZPL layer now registers a callback to drop these dentries removing a layering violation which dates back to the Solaris code. This callback can also be used by other ARC consumers such as Lustre. arc_add_prune_callback() arc_remove_prune_callback() * The arc_reduce_dnlc_percent module option has been changed to arc_meta_prune for clarity. The dnlc functions are specific to Solaris's VFS and have already been largely eliminated already. The replacement tunable now represents the number of bytes the prune callback will request when invoked. * Less aggressively invoke the prune callback. We used to call this whenever we exceeded the arc_meta_limit however that's not strictly correct since it results in over zeleous reclaim of dentries and inodes. It is now only called once the arc_meta_limit is exceeded and every effort has been made to evict other data from the ARC cache. * More promptly manage exceeding the arc_meta_limit. When reading meta data in to the cache if a buffer was unable to be recycled notify the arc_reclaim thread to invoke the required prune. * Added arcstat_prune kstat which is incremented when the ARC is forced to request that a consumer prune its cache. Remember this will only occur when the ARC has no other choice. If it can evict buffers safely without invoking the prune callback it will. * This change is also expected to resolve the unexpect collapses of the ARC cache. This would occur because when exceeded just the arc_meta_limit reclaim presure would be excerted on the arc_c value via arc_shrink(). This effectively shrunk the entire cache when really we just needed to reclaim meta data. Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes #466 Closes #292 |
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Brian Behlendorf
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6283f55ea1 |
Support custom build directories and move includes
One of the neat tricks an autoconf style project is capable of is allow configurion/building in a directory other than the source directory. The major advantage to this is that you can build the project various different ways while making changes in a single source tree. For example, this project is designed to work on various different Linux distributions each of which work slightly differently. This means that changes need to verified on each of those supported distributions perferably before the change is committed to the public git repo. Using nfs and custom build directories makes this much easier. I now have a single source tree in nfs mounted on several different systems each running a supported distribution. When I make a change to the source base I suspect may break things I can concurrently build from the same source on all the systems each in their own subdirectory. wget -c http://github.com/downloads/behlendorf/zfs/zfs-x.y.z.tar.gz tar -xzf zfs-x.y.z.tar.gz cd zfs-x-y-z ------------------------- run concurrently ---------------------- <ubuntu system> <fedora system> <debian system> <rhel6 system> mkdir ubuntu mkdir fedora mkdir debian mkdir rhel6 cd ubuntu cd fedora cd debian cd rhel6 ../configure ../configure ../configure ../configure make make make make make check make check make check make check This change also moves many of the include headers from individual incude/sys directories under the modules directory in to a single top level include directory. This has the advantage of making the build rules cleaner and logically it makes a bit more sense. |