[PATCH] memory: bail from page scrubbing when CPU is no longer online

* [PATCH] memory: bail from page scrubbing when CPU is no longer online
@ 2021-01-28 10:35 Jan Beulich
  2021-01-28 10:37 ` Andrew Cooper
  0 siblings, 1 reply; 2+ messages in thread
From: Jan Beulich @ 2021-01-28 10:35 UTC (permalink / raw)
  To: xen-devel
  Cc: Andrew Cooper, George Dunlap, Ian Jackson, Julien Grall,
	Stefano Stabellini, Wei Liu

Scrubbing can significantly delay the offlining (parking) of a CPU (e.g.
because of booting into in smt=0 mode), to a degree that the "CPU <n>
still not dead..." messages logged on x86 in 1s intervals can be seen
multiple times. There are no softirqs involved in this process, so
extend the existing preemption check in the scrubbing logic to also exit
when the CPU is no longer observed online.

Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -1324,9 +1324,11 @@ bool scrub_free_pages(void)
                      * Scrub a few (8) pages before becoming eligible for
                      * preemption. But also count non-scrubbing loop iterations
                      * so that we don't get stuck here with an almost clean
-                     * heap.
+                     * heap. Consider the CPU no longer being seen as online as
+                     * a request to preempt immediately, to not unduly delay
+                     * its offlining.
                      */
-                    if ( cnt > 800 && softirq_pending(cpu) )
+                    if ( !cpu_online(cpu) || (cnt > 800 && softirq_pending(cpu)) )
                     {
                         preempt = true;
                         break;


^ permalink raw reply	[flat|nested] 2+ messages in thread