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Matthew Ahrens 67c0f0dedc
ARC shrinking blocks reads/writes 
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 commit 3ec34e5527, 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 commit
3ec34e5527.

Note: commit 3ec34e5527 is `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
2020-06-26 10:42:27 -07:00
.github Update wiki links with new address 2020-06-03 19:46:31 -07:00
cmd Fix check for sed --in-place 2020-06-24 18:19:59 -07:00
config pam: implement a zfs_key pam module 2020-06-24 18:45:44 -07:00
contrib pam: implement a zfs_key pam module 2020-06-24 18:45:44 -07:00
etc Drop unnecessary srcdir paths 2020-06-24 18:20:18 -07:00
include ARC shrinking blocks reads/writes 2020-06-26 10:42:27 -07:00
lib Drop unnecessary srcdir paths 2020-06-24 18:20:18 -07:00
man zed additional features 2020-06-22 09:53:34 -07:00
module ARC shrinking blocks reads/writes 2020-06-26 10:42:27 -07:00
rpm pam: implement a zfs_key pam module 2020-06-24 18:45:44 -07:00
scripts Drop unnecessary srcdir paths 2020-06-24 18:20:18 -07:00
tests pam: implement a zfs_key pam module 2020-06-24 18:45:44 -07:00
udev Drop unnecessary srcdir paths 2020-06-24 18:20:18 -07:00
.editorconfig Add an .editorconfig; document git whitespace settings 2020-01-27 13:32:52 -08:00
.gitignore Add FreeBSD support to OpenZFS 2020-04-14 11:36:28 -07:00
.gitmodules Add zimport.sh compatibility test script 2014-02-21 12:10:31 -08:00
.travis.yml Add .travis.yml 2017-11-13 09:18:18 -08:00
AUTHORS Update build system and packaging 2018-05-29 16:00:33 -07:00
autogen.sh Cause autogen.sh to fail if autoreconf fails 2018-07-06 09:27:37 -07:00
CODE_OF_CONDUCT.md Add CODE_OF_CONDUCT.md 2019-04-30 10:58:45 -07:00
configure.ac pam: implement a zfs_key pam module 2020-06-24 18:45:44 -07:00
copy-builtin Move zfs_gitrev.h to build directory 2020-06-24 18:19:28 -07:00
COPYRIGHT Fix typos 2020-06-09 21:24:09 -07:00
LICENSE Update build system and packaging 2018-05-29 16:00:33 -07:00
Makefile.am Fix check for sed --in-place 2020-06-24 18:19:59 -07:00
META Linux 5.7 compat: blk_alloc_queue() 2020-04-09 09:16:46 -07:00
NEWS Add NEWS file 2018-09-18 12:03:47 -07:00
NOTICE Update build system and packaging 2018-05-29 16:00:33 -07:00
README.md Update wiki links with new address 2020-06-03 19:46:31 -07:00
TEST Remove CI builder customization from TEST 2020-03-16 10:46:03 -07:00
zfs.release.in Move zfs.release generation to configure step 2012-07-12 12:22:51 -07:00

README.md

img

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.

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Official Resources

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 META file contains the officially recognized supported Linux kernel versions.
  • Supported FreeBSD versions are 12-STABLE and 13-CURRENT.