On 17-Mar-25 8:35 PM, Gregory Price wrote:
On Mon, Mar 17, 2025 at 09:09:18AM +0530, Bharata B Rao wrote:
On 13-Mar-25 10:14 PM, Davidlohr Bueso wrote:
On Thu, 06 Mar 2025, Bharata B Rao wrote:
+static int page_should_be_promoted(struct page_hotness_info *phi)
+{
+ struct page *page = pfn_to_online_page(phi->pfn);
+ unsigned long now = jiffies;
+ struct folio *folio;
+
+ if (!page || is_zone_device_page(page))
+ return false;
+
+ folio = page_folio(page);
+ if (!folio_test_lru(folio)) {
+ count_vm_event(KPROMOTED_MIG_NON_LRU);
+ return false;
+ }
+ if (folio_nid(folio) == phi->hot_node) {
+ count_vm_event(KPROMOTED_MIG_RIGHT_NODE);
+ return false;
+ }
How about using the LRU age itself:
Sounds like a good check for page hotness.
if (folio_test_active())
return true;
But the numbers I obtained with this check added, didn't really hit this
condition all that much. I was running a multi-threaded application that
allocates enough memory such that the allocation spills over from DRAM node
to the CXL node. Threads keep touching the memory pages in random order.
Is demotion enabled by any chance?
Yes, I thought enabling demotion is required to create enough room in
the toptier to handle promotion.
i.e. are you sure it's actually allocating from CXL and not demoting
cold stuff to CXL?
But then I realized that spill over was caused by demotion rather than
initial allocation even when I used MPOL_BIND | MPOL_F_NUMA_BALANCING
policy with both toptier and CXL node in the nodemask.
kpromoted_recorded_accesses 960620 /* Number of recorded accesses */
kpromoted_recorded_hwhints 960620 /* Nr accesses via HW hints, IBS in this
case */
kpromoted_recorded_pgtscans 0
kpromoted_record_toptier 638006 /* Nr toptier accesses */
kpromoted_record_added 321234 /* Nr (CXL) accesses that are tracked */
kpromoted_record_exists 1380
kpromoted_mig_right_node 0
kpromoted_mig_non_lru 226
kpromoted_mig_lru_active 47 /* Number of accesses considered for promotion
as determined by folio_test_active() check */
However disabling demotion has no impact on this number (and hence the
folio_test_active() check)
Regards,
Bharata.
