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ARC: parallel eviction

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On systems with enormous amounts of memory, the single arc_evict thread
can become a bottleneck if reads and writes are stuck behind it, waiting
for old data to be evicted before new data can take its place.

This commit adds support for evicting from multiple ARC lists in
parallel, by farming the evict work out to some number of threads and
then accumulating their results.

A new tuneable, zfs_arc_evict_threads, sets the number of threads. By
default, it will scale based on the number of CPUs.

Sponsored-by: Expensify, Inc.
Sponsored-by: Klara, Inc.
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Youzhong Yang <youzhong@gmail.com>
Signed-off-by: Allan Jude <allan@klarasystems.com>
Signed-off-by: Mateusz Piotrowski <mateusz.piotrowski@klarasystems.com>
Signed-off-by: Alexander Stetsenko <alex.stetsenko@klarasystems.com>
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
Co-authored-by: Rob Norris <rob.norris@klarasystems.com>
Co-authored-by: Mateusz Piotrowski <mateusz.piotrowski@klarasystems.com>
Co-authored-by: Alexander Stetsenko <alex.stetsenko@klarasystems.com>
Closes #16486
This commit is contained in:
Allan Jude
2025-05-14 10:38:32 -04:00
committed by Brian Behlendorf
parent 6b67a5bdd3
commit 8e9ffe1b4f
2 changed files with 233 additions and 21 deletions
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man/man4/zfs.4
+36 -4
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@@ -3,7 +3,7 @@
.\" Copyright (c) 2013 by Turbo Fredriksson <turbo@bayour.com>. All rights reserved.
.\" Copyright (c) 2019, 2021 by Delphix. All rights reserved.
.\" Copyright (c) 2019 Datto Inc.
.\" Copyright (c) 2023, 2024 Klara, Inc.
.\" Copyright (c) 2023, 2024, 2025, Klara, Inc.
.\" The contents of this file are subject to the terms of the Common Development
.\" and Distribution License (the "License"). You may not use this file except
.\" in compliance with the License. You can obtain a copy of the license at
@@ -17,9 +17,7 @@
.\" own identifying information:
.\" Portions Copyright [yyyy] [name of copyright owner]
.\"
.\" Copyright (c) 2024, Klara, Inc.
.\"
.Dd November 1, 2024
.Dd May 7, 2025
.Dt ZFS 4
.Os
.
@@ -725,6 +723,40 @@ Number ARC headers to evict per sub-list before proceeding to another sub-list.
This batch-style operation prevents entire sub-lists from being evicted at once
but comes at a cost of additional unlocking and locking.
.
.It Sy zfs_arc_evict_threads Ns = Ns Sy 0 Pq int
Sets the number of ARC eviction threads to be used.
.Pp
If set greater than 0, ZFS will dedicate up to that many threads to ARC
eviction.
Each thread will process one sub-list at a time,
until the eviction target is reached or all sub-lists have been processed.
When set to 0, ZFS will compute a reasonable number of eviction threads based
on the number of CPUs.
.TS
box;
lb l l .
CPUs Threads
_
1-4 1
5-8 2
9-15 3
16-31 4
32-63 6
64-95 8
96-127 9
128-160 11
160-191 12
192-223 13
224-255 14
256+ 16
.TE
.Pp
More threads may improve the responsiveness of ZFS to memory pressure.
This can be important for performance when eviction from the ARC becomes
a bottleneck for reads and writes.
.Pp
This parameter can only be set at module load time.
.
.It Sy zfs_arc_grow_retry Ns = Ns Sy 0 Ns s Pq uint
If set to a non zero value, it will replace the
.Sy arc_grow_retry