On 6/17/20 1:53 PM, Andrew Morton wrote:
On Tue, 16 Jun 2020 13:45:27 -0700 Nitin Gupta <nigupta@xxxxxxxxxx> wrote:
For some applications, we need to allocate almost all memory as
hugepages. However, on a running system, higher-order allocations can
fail if the memory is fragmented. Linux kernel currently does on-demand
compaction as we request more hugepages, but this style of compaction
incurs very high latency. Experiments with one-time full memory
compaction (followed by hugepage allocations) show that kernel is able
to restore a highly fragmented memory state to a fairly compacted memory
state within <1 sec for a 32G system. Such data suggests that a more
proactive compaction can help us allocate a large fraction of memory as
hugepages keeping allocation latencies low.
...
All looks straightforward to me and easy to disable if it goes wrong.
All the hard-coded magic numbers are a worry, but such is life.
One teeny complaint:
...
@@ -2650,12 +2801,34 @@ static int kcompactd(void *p)
unsigned long pflags;
trace_mm_compaction_kcompactd_sleep(pgdat->node_id);
- wait_event_freezable(pgdat->kcompactd_wait,
- kcompactd_work_requested(pgdat));
+ if (wait_event_freezable_timeout(pgdat->kcompactd_wait,
+ kcompactd_work_requested(pgdat),
+ msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC))) {
+
+ psi_memstall_enter(&pflags);
+ kcompactd_do_work(pgdat);
+ psi_memstall_leave(&pflags);
+ continue;
+ }
- psi_memstall_enter(&pflags);
- kcompactd_do_work(pgdat);
- psi_memstall_leave(&pflags);
+ /* kcompactd wait timeout */
+ if (should_proactive_compact_node(pgdat)) {
+ unsigned int prev_score, score;
Everywhere else, scores have type `int'. Here they are unsigned. How come?
Would it be better to make these unsigned throughout? I don't think a
score can ever be negative?
The score is always in [0, 100], so yes, it should be unsigned.
I will send another patch which fixes this.
Thanks,
Nitin
