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Matthew Ahrens
67c0f0dedc
ZFS registers a memory hook, `__arc_shrinker_func`, which is supposed to allow the ARC to shrink when the kernel experiences memory pressure. The ARC shrinker changes `arc_c` via a call to `arc_reduce_target_size()`. Before commit3ec34e5527, the ARC shrinker would also evict data from the ARC to bring `arc_size` down to the new `arc_c`. However, that commit (seemingly inadvertently) made it so that the ARC shrinker no longer evicts any data or waits for eviction to complete. Repeated calls to the ARC shrinker can reduce `arc_c` drastically, often all the way to `arc_c_min`. Since it doesn't wait for the actual eviction of data from the ARC, this creates a situation where `arc_size` is more than `arc_c` for the several seconds/minutes it takes for `arc_adjust_zthr` to evict data from the ARC. During this time, arc_get_data_impl() will block, so ZFS can't process read/write requests (e.g. from iSCSI, NFS, or read/write syscalls). To ensure that `arc_c` doesn't shrink faster than the adjust thread can keep up, this commit makes the ARC shrinker wait for the eviction to complete, resulting in similar behavior to what we had before commit3ec34e5527. Note: commit3ec34e5527is `OpenZFS 9284 - arc_reclaim_thread has 2 jobs` and was integrated in December 2018, and is part of ZoL 0.8.x but not 0.7.x. Additionally, when the ARC size is reduced drastically, the `arc_adjust_zthr` can be on-CPU for many seconds without blocking. Any threads that are bound to the same CPU that arc_adjust_zthr is running on will not able to run for a long time. To ensure that CPU-bound threads can make progress, this commit changes `arc_evict_state_impl()` make a voluntary preemption call, `cond_resched()`. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: George Wilson <gwilson@delphix.com> Reviewed-by: Prakash Surya <prakash.surya@delphix.com> Reviewed-by: Pavel Zakharov <pavel.zakharov@delphix.com> Reviewed-by: Tony Nguyen <tony.nguyen@delphix.com> Signed-off-by: Matthew Ahrens <mahrens@delphix.com> External-issue: DLPX-70703 Closes #10496
OpenZFS is an advanced file system and volume manager which was originally developed for Solaris and is now maintained by the OpenZFS community. This repository contains the code for running OpenZFS on Linux and FreeBSD.
Official Resources
- Documentation - for using and developing this repo
- ZoL Site - Linux release info & links
- Mailing lists
- OpenZFS site - for conference videos and info on other platforms (illumos, OSX, Windows, etc)
Installation
Full documentation for installing OpenZFS on your favorite Linux distribution can be found at the ZoL Site.
Contribute & Develop
We have a separate document with contribution guidelines.
We have a Code of Conduct.
Release
OpenZFS is released under a CDDL license.
For more details see the NOTICE, LICENSE and COPYRIGHT files; UCRL-CODE-235197
Supported Kernels
- The
METAfile contains the officially recognized supported Linux kernel versions. - Supported FreeBSD versions are 12-STABLE and 13-CURRENT.