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vmstat: explicitly schedule per-cpu work on the CPU we need it to run on

The vmstat code uses "schedule_delayed_work_on()" to do the initial
startup of the delayed work on the right CPU, but then once it was
started it would use the non-cpu-specific "schedule_delayed_work()" to
re-schedule it on that CPU.

That just happened to schedule it on the same CPU historically (well, in
almost all situations), but the code _requires_ this work to be per-cpu,
and should say so explicitly rather than depend on the non-cpu-specific
scheduling to schedule on the current CPU.

The timer code is being changed to not be as single-minded in always
running things on the calling CPU.

See also commit 874bbfe600a6 ("workqueue: make sure delayed work run in
local cpu") that for now maintains the local CPU guarantees just in case
there are other broken users that depended on the accidental behavior.

Cc: Christoph Lameter <cl@linux.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Linus Torvalds 176bed1d 995e2fe9

+4 -3
+4 -3
mm/vmstat.c
··· 1363 1363 1364 1364 static void vmstat_update(struct work_struct *w) 1365 1365 { 1366 - if (refresh_cpu_vm_stats()) 1366 + if (refresh_cpu_vm_stats()) { 1367 1367 /* 1368 1368 * Counters were updated so we expect more updates 1369 1369 * to occur in the future. Keep on running the 1370 1370 * update worker thread. 1371 1371 */ 1372 - schedule_delayed_work(this_cpu_ptr(&vmstat_work), 1372 + schedule_delayed_work_on(smp_processor_id(), 1373 + this_cpu_ptr(&vmstat_work), 1373 1374 round_jiffies_relative(sysctl_stat_interval)); 1374 - else { 1375 + } else { 1375 1376 /* 1376 1377 * We did not update any counters so the app may be in 1377 1378 * a mode where it does not cause counter updates.