Viewing: llite.pcc_attach_thread_max.4
.TH LLITE.PCC_ATTACH_THREAD_MAX 4 2026-08-26 "Lustre" "Lustre Kernel Interfaces"
.SH NAME
llite.pcc_attach_thread_max \- limit number of PCC copy threads per mount
.SH SYNOPSIS
.SY
.RI "lctl get_param llite." FSNAME *.pcc_attach_thread_max
.SY
.RI "lctl set_param llite." FSNAME *.pcc_attach_thread_max= THREAD_COUNT
.YS
.SS PROPERTIES
.TP
.B Access Permissions
.br
.BR 644 " | " -rw-r--r--
.TP
.B Scope
.br
Per local filesystem mountpoint.
.TP
.B Config
.br
.B pcc_attach_thread_max
is always present for client mountpoints.
.TP
.B Default
.br
.RB pcc_attach_thread_max= 1024
.TP
.B Valid Range
.br
.RB pcc_attach_thread_max= 1
.br
.RB pcc_attach_thread_max= 16384
.SH DESCRIPTION
The Persistent Client Cache file attach process starts background file
copy threads when a cache-eligible file is accessed to perform the
.BR lfs-pcc-attach (1)
operation. The specified
.I THREAD_COUNT
is the maximum number of background threads started on each mountpoint.
The limit is advisory: the running count is sampled before the attach is
set up and is only incremented during that setup, so threads entering the
attach path at the same time can each pass the check. The number of
running threads can exceed
.I THREAD_COUNT
by the number of such threads, for as long as their copies take.
Once the limit is reached the attach is done synchronously inside
.BR open (2)
rather than in a background thread, so the opening process blocks until
the copy finishes.
The default
.B 1024
limit is expected to be sufficient for most uses, but is tunable up or down.
.SH MODULES
This parameter is in the following modules:
.EX
.B llite.*.pcc_attach_thread_max
.EE
.SH EXAMPLES
Permanently limit the number of background copy threads per mountpoint to 16:
.EX
.RB "mgs# " "lctl set_param -P llite.*.pcc_attach_thread_max=16"
.EE
.PP
Limit the number of background copy threads to 32 for the
.B testfs
filesystem on the local
.BR client :
.EX
.RB "client# " "lctl set_param llite.testfs-*.pcc_attach_thread_max=32"
.EE
.SH AVAILABILITY
The
.B llite.pcc_attach_thread_max
parameter is part of the
.BR lustre (7)
filesystem package since release 2.18.0.
.\" Added in commit v2_17_57-117-g9106323881
.SH SEE ALSO
.BR lfs-pcc-attach (1),
.BR lctl-get_param (8),
.BR lctl-set_param (8)
