On 7/2/2025 1:58 AM, Libo Chen wrote:
Hi Chenyu
On 7/1/25 09:36, Chen, Yu C wrote:
+
/*
* Got a PROT_NONE fault for a page on @node.
*/
@@ -3189,6 +3212,9 @@ void task_numa_fault(int last_cpupid, int mem_node, int pages, int flags)
!cpupid_valid(last_cpupid)))
return;
+ if (!tg_numa_balance_enabled(p))
+ return;
+
I think this one may be redundant when you already have it in task_numa_work(). Without the
scanning, there won't be any hinting page faults on that task, so neither do_numa_page() nor
do_huge_pmd_numa_page() will be called. Though it's a minor issue if tg_numa_balance_enabled(p)
is fast.
Previously I was thinking of the following sequence:
1. the NUMA balancing is enabled and task_numa_work() is invoked,
pages are scanned and PROT_NONE is set.
2. cgroup NUMA balancing is disabled by the user
3. do_numa_page() is triggered and PROT_NONE is cleared.
We don't want to do further task migration and
task_numa_fault() bails out.(page migration is still
allowed as we mainly want to control the behavior of
the task)
Ah right, that makes sense. Does that fall under unlikely()? The timing window seems to be
quite small to me.
Yup, and I guess that depends on how often the task access the
"invalid" address - it might take quite some time after the
page been set invalid and then the task access it to trigger
a page fault.
Thanks,
Chenyu
