From: Nathan Lynch Date: Mon, 24 Jun 2019 17:03:00 +0000 (+0200) Subject: powerpc/numa: document topology_updates_enabled, disable by default X-Git-Tag: Ubuntu-4.15.0-55.60~27 X-Git-Url: https://git.proxmox.com/?p=mirror_ubuntu-bionic-kernel.git;a=commitdiff_plain;h=d4233704c684072a62bdd7047c84054bc99defb3 powerpc/numa: document topology_updates_enabled, disable by default Changing the NUMA associations for CPUs and memory at runtime is basically unsupported by the core mm, scheduler etc. We see all manner of crashes, warnings and instability when the pseries code tries to do this. Disable this behavior by default, and document the switch a bit. BugLink: https://bugs.launchpad.net/bugs/1833716 Signed-off-by: Nathan Lynch Signed-off-by: Michael Ellerman (cherry picked from commit 558f86493df09f68f79fe056d9028d317a3ce8ab) Signed-off-by: Manoj Iyer Acked-by: Stefan Bader Acked-by: Kleber Sacilotto de Souza Signed-off-by: Kleber Sacilotto de Souza --- diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c index 77424112184a..ff906f251f4b 100644 --- a/arch/powerpc/mm/numa.c +++ b/arch/powerpc/mm/numa.c @@ -981,16 +981,22 @@ static int __init early_numa(char *p) } early_param("numa", early_numa); -static bool topology_updates_enabled = true; +/* + * The platform can inform us through one of several mechanisms + * (post-migration device tree updates, PRRN or VPHN) that the NUMA + * assignment of a resource has changed. This controls whether we act + * on that. Disabled by default. + */ +static bool topology_updates_enabled; static int __init early_topology_updates(char *p) { if (!p) return 0; - if (!strcmp(p, "off")) { - pr_info("Disabling topology updates\n"); - topology_updates_enabled = false; + if (!strcmp(p, "on")) { + pr_warn("Caution: enabling topology updates\n"); + topology_updates_enabled = true; } return 0;