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Introduce limit on size of L2ARC headers

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Since L2ARC buffers are not evicted on memory pressure, too large
amount of headers on system with irrationally large L2ARC can render
it slow or even unusable.  This change limits L2ARC writes and
rebuild if unevictable L2ARC-only headers reach dangerous level.

While there, call arc_adapt() on L2ARC rebuild, so that it could
properly grow arc_c, reflecting potentially significant ARC size
increase and avoiding slow growth with hopeless eviction attempts
later when "overflow" is detected.

Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reported-by: Richard Elling <Richard.Elling@RichardElling.com>
Signed-off-by: Alexander Motin <mav@FreeBSD.org>
Closes #10765
This commit is contained in:
Alexander Motin
2020-08-25 17:33:36 -04:00
committed by Brian Behlendorf
parent 47a3f3fc01
commit 3ca31bd0c6
2 changed files with 36 additions and 5 deletions
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man/man5/zfs-module-parameters.5
+14
View File
@@ -198,6 +198,20 @@ feature.
Default value: \fB200\fR%.
.RE
.sp
.ne 2
.na
\fBl2arc_meta_percent\fR (int)
.ad
.RS 12n
Percent of ARC size allowed for L2ARC-only headers.
Since L2ARC buffers are not evicted on memory pressure, too large amount of
headers on system with irrationaly large L2ARC can render it slow or unusable.
This parameter limits L2ARC writes and rebuild to achieve it.
.sp
Default value: \fB33\fR%.
.RE
.sp
.ne 2
.na