From: Ridong Chen <[email protected]>
Background
==========
MGLRU currently has no tracepoints of its own. The scan and evict paths
reuse the classic-LRU tracepoints (trace_mm_vmscan_lru_isolate() and
trace_mm_vmscan_lru_shrink_inactive()), which predate MGLRU and carry no
generation, sequence, memcg or swappiness context. A trace of a running
system therefore cannot tell which memcg a given scan belongs to, how far
reclaim has progressed through the generations, or when a new generation
is created - so how MGLRU actually operates is effectively invisible.
Implementation
==============
Patch 1 is a cleanup that factors the per-generation page-count
summation into a helper, lru_gen_seq_nr_pages(), reused by patch 3.
Patch 2 adds mm_mglru_scan_folios on the scan path, and patch 3 adds
mm_mglru_inc_max_seq on the aging path. Both carry the memcg id and the
generation window (min_seq/max_seq), live at MGLRU-specific layers with
no classic-LRU counterpart, and are guarded so the hot paths stay
zero-cost when disabled.
Effect
======
Paired, the two tracepoints make the full aging-to-eviction window
observable per memcg: aging advances max_seq (the leading edge), scanning
consumes the oldest generations, and the min_seq/max_seq pair on each
event shows how the generation window moves over time.
A sample trace, with the classic-LRU tracepoints left enabled to show
how they interleave:
mm_vmscan_lru_isolate: classzone=4 order=0 nr_requested=36 nr_scanned=31
nr_skipped=0 nr_taken=29 lru=inactive_file
mm_mglru_scan_folios: memcg_id=73 classzone=4 order=0 nr_requested=36
nr_scanned=31 nr_sorted=2 nr_skipped=0 nr_taken=29 lru=inactive_file max_seq=3
tier=3 min_seq=0
mm_vmscan_lru_shrink_inactive: nid=0 nr_scanned=31 nr_reclaimed=29 nr_dirty=0
nr_writeback=0 nr_congested=0 nr_immediate=0 nr_activate_anon=0
nr_activate_file=0 nr_ref_keep=0 nr_unmap_fail=0 priority=5
flags=RECLAIM_WB_FILE|RECLAIM_WB_ASYNC
mm_mglru_inc_max_seq: memcg_id=73 max_seq=4 anon_min_seq=1 file_min_seq=1
nr_anon={0x0,0x0,0x1,0x0} nr_file={0x0,0x427,0x6,0x4a}
mm_vmscan_lru_isolate: classzone=4 order=0 nr_requested=5 nr_scanned=5
nr_skipped=0 nr_taken=1 lru=inactive_file
mm_mglru_scan_folios: memcg_id=73 classzone=4 order=0 nr_requested=5
nr_scanned=5 nr_sorted=4 nr_skipped=0 nr_taken=1 lru=inactive_file max_seq=4
tier=3 min_seq=1
mm_vmscan_lru_shrink_inactive: nid=0 nr_scanned=5 nr_reclaimed=1 nr_dirty=0
nr_writeback=0 nr_congested=0 nr_immediate=0 nr_activate_anon=0
nr_activate_file=0 nr_ref_keep=0 nr_unmap_fail=0 priority=5
flags=RECLAIM_WB_FILE|RECLAIM_WB_ASYNC
The mm_mglru_scan_folios lines carry the memcg id and the generation
window (max_seq/min_seq) that the bare mm_vmscan_lru_isolate lines above
them cannot - those cannot even say which memcg they came from. The
mm_mglru_inc_max_seq line then shows a new generation being created
(max_seq 3 -> 4) with the per-generation page counts for both types.
---
v2: address Sashiko AI review [1] - pass struct lruvec * into the tracepoints
and do the memcg lookup inside TP_fast_assign.
[1]
https://sashiko.dev/#/patchset/[email protected]?part=2
Ridong Chen (3):
mm/mglru: factor out lru_gen_seq_nr_pages()
mm/mglru: add tracepoint for scan_folios()
mm/mglru: add tracepoint for inc_max_seq()
include/trace/events/vmscan.h | 101 ++++++++++++++++++++++++++++++++++
mm/vmscan.c | 53 +++++++++++++++---
2 files changed, 146 insertions(+), 8 deletions(-)
--
2.34.1
