# Re: \[PATCH v5 5/6\] mm/mglru: add tracepoint for scan\_folios() - From: Barry Song \ - Date: 2026-10-31 21:02:51 - List: linux-trace-kernel - Page: https://ratatoskr.run/linux-trace-kernel/2026/10/17838482 - Thread: https://ratatoskr.run/linux-trace-kernel/2026/10/17837167/t.md ```text On Sat, Oct 31, 2026 at 5:01 PM Ridong Chen [ref] wrote: > > From: Ridong Chen > > MGLRU's scan_folios() emits the classic-LRU tracepoint > trace_mm_vmscan_lru_isolate(), which predates MGLRU. It reports the > scan/isolate counts and the LRU type, but carries no generation or > memcg context, so a trace of an MGLRU run cannot tell which memcg a > given scan belongs to, nor how far reclaim has progressed through the > generations. > > Add mm_mglru_scan_folios next to it, reporting the same counters plus > nr_sorted (folios moved to a younger generation by sort_folio()) and > the context the classic tracepoint lacks: the node id and memcg id of > the lruvec, and the max_seq, tier and min_seq of the type being > scanned. > > Now that struct scan_control is visible to the trace header, pass sc, > lruvec, type and tier straight in and derive everything else in > TP_fast_assign(), so nothing is computed at the call site when the > event is disabled. The int fields are grouped at the end of the entry > to avoid padding on 64-bit. > > scan_folios() is the MGLRU-specific layer where folios are actually > scanned, so it has no classic-LRU counterpart. The existing tracepoint > is left unchanged. > > Signed-off-by: Ridong Chen > --- Ran a test on this: /sys/kernel/tracing/events/vmscan/mm_mglru_scan_folios # cat format name: mm_mglru_scan_folios ID: 491 format: field:unsigned short common_type; offset:0; size:2; signed:0; field:unsigned char common_flags; offset:2; size:1; signed:0; field:unsigned char common_preempt_count; offset:3; size:1; signed:0; field:int common_pid; offset:4; size:4; signed:1; field:u64 memcg_id; offset:8; size:8; signed:0; field:unsigned long nr_requested; offset:16; size:8; signed:0; field:unsigned long nr_scanned; offset:24; size:8; signed:0; field:unsigned long nr_sorted; offset:32; size:8; signed:0; field:unsigned long nr_skipped; offset:40; size:8; signed:0; field:unsigned long nr_taken; offset:48; size:8; signed:0; field:unsigned long max_seq; offset:56; size:8; signed:0; field:unsigned long min_seq; offset:64; size:8; signed:0; field:int nid; offset:72; size:4; signed:1; field:int highest_zoneidx; offset:76; size:4; signed:1; field:int order; offset:80; size:4; signed:1; field:int lru; offset:84; size:4; signed:1; field:int tier; offset:88; size:4; signed:1; print fmt: "nid=%d memcg_id=%llu classzone=%d order=%d nr_requested=%lu nr_scanned=%lu nr_sorted=%lu nr_skipped=%lu nr_taken=%lu lru=%s max_seq=%lu tier=%d min_seq=%lu", REC->nid, REC->memcg_id, REC->highest_zoneidx, REC->order, REC->nr_requested, REC->nr_scanned, REC->nr_sorted, REC->nr_skipped, REC->nr_taken, __print_symbolic(REC->lru, {0, "inactive_anon"}, {1, "active_anon"}, {2, "inactive_file"}, {3, "active_file"}, {4, "unevictable"}), REC->max_seq, REC->tier, REC->min_seq ~ # echo 1 > /sys/kernel/tracing/events/vmscan/mm_mglru_scan_folios/enable ~ # ./a.out [+] mapped 500 MB at 0xffff9f000000 (128000 pages) [+] duration: 60 seconds [+] first pass done, start looping writes ^C ~ # cat /sys/kernel/tracing/trace | grep mglru_scan_folios | head kswapd0-50 [000] d..1. 650.877105: mm_mglru_scan_folios: nid=0 memcg_id=1 classzone=2 order=0 nr_requested=64 nr_scanned=0 nr_sorted=0 nr_skipped=0 nr_taken=0 lru=inactive_anon max_seq=3 tier=3 min_seq=1 kswapd0-50 [000] d..1. 650.877686: mm_mglru_scan_folios: nid=0 memcg_id=1 classzone=2 order=0 nr_requested=64 nr_scanned=64 nr_sorted=0 nr_skipped=0 nr_taken=64 lru=inactive_file max_seq=3 tier=3 min_seq=0 kswapd0-50 [000] d..1. 650.907558: mm_mglru_scan_folios: nid=0 memcg_id=1 classzone=2 order=0 nr_requested=64 nr_scanned=0 nr_sorted=0 nr_skipped=0 nr_taken=0 lru=inactive_anon max_seq=3 tier=3 min_seq=1 kswapd0-50 [000] d..1. 650.907729: mm_mglru_scan_folios: nid=0 memcg_id=1 classzone=2 order=0 nr_requested=64 nr_scanned=64 nr_sorted=0 nr_skipped=0 nr_taken=64 lru=inactive_file max_seq=3 tier=3 min_seq=0 kswapd0-50 [000] d..1. 650.909040: mm_mglru_scan_folios: nid=0 memcg_id=1 classzone=2 order=0 nr_requested=64 nr_scanned=0 nr_sorted=0 nr_skipped=0 nr_taken=0 lru=inactive_anon max_seq=3 tier=3 min_seq=1 kswapd0-50 [000] d..1. 650.909198: mm_mglru_scan_folios: nid=0 memcg_id=1 classzone=2 order=0 nr_requested=64 nr_scanned=64 nr_sorted=0 nr_skipped=0 nr_taken=64 lru=inactive_file max_seq=3 tier=3 min_seq=0 kswapd0-50 [000] d..1. 650.910520: mm_mglru_scan_folios: nid=0 memcg_id=1 classzone=2 order=0 nr_requested=64 nr_scanned=0 nr_sorted=0 nr_skipped=0 nr_taken=0 lru=inactive_anon max_seq=3 tier=3 min_seq=1 kswapd0-50 [000] d..1. 650.910710: mm_mglru_scan_folios: nid=0 memcg_id=1 classzone=2 order=0 nr_requested=64 nr_scanned=64 nr_sorted=4 nr_skipped=0 nr_taken=60 lru=inactive_file max_seq=3 tier=3 min_seq=0 kswapd0-50 [000] d..1. 650.911866: mm_mglru_scan_folios: nid=0 memcg_id=1 classzone=2 order=0 nr_requested=64 nr_scanned=0 nr_sorted=0 nr_skipped=0 nr_taken=0 lru=inactive_anon max_seq=3 tier=3 min_seq=1 kswapd0-50 [000] d..1. 650.911988: mm_mglru_scan_folios: nid=0 memcg_id=1 classzone=2 order=0 nr_requested=64 nr_scanned=66 nr_sorted=0 nr_skipped=0 nr_taken=66 lru=inactive_file max_seq=3 tier=3 min_seq=0 The LRU naming feels a bit weird to me. We have "inactive_file" and "inactive_anon", but MGLRU doesn't have active/inactive lists. I guess it's not a big issue, though, since we also use the same names in trace_mm_vmscan_lru_isolate() in scan_folios(). For the patch: Tested-by: Barry Song Reviewed-by: Barry Song ```