docs: net: document neigh gc_stale_time sysctl

Add missing documentation for a neighbor table garbage collector sysctl
parameter in ip-sysctl.rst:

neigh/default/gc_stale_time: controls how long an unused neighbor entry
is kept before becoming eligible for garbage collection (default: 60
seconds)

Signed-off-by: Gabriel Goller <g.goller@proxmox.com>
Link: https://patch.msgid.link/20260223101257.47563-1-g.goller@proxmox.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index 6921d8594b8493a25d62ffd586d0b9f6527409cb..9c90333530fa9ed02c104d146ca650414d91149b 100644 (file)
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -202,6 +202,17 @@ neigh/default/gc_thresh3 - INTEGER
 
        Default: 1024
 
+neigh/default/gc_stale_time - INTEGER
+       Determines how long a neighbor entry can remain unused before it is
+       considered stale and eligible for garbage collection. Entries that have
+       not been used for longer than this time will be removed by the garbage
+       collector, unless they have active references, are marked as PERMANENT,
+       or carry the NTF_EXT_LEARNED or NTF_EXT_VALIDATED flag. Stale entries
+       are only removed by the periodic GC when there are at least gc_thresh1
+       neighbors in the table.
+
+       Default: 60 seconds
+
 neigh/default/unres_qlen_bytes - INTEGER
        The maximum number of bytes which may be used by packets
        queued for each unresolved address by other network layers.