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Fri, 11 Sep 2026 07:29:08 +0000 X-Mizu-Trace-ID: 047fe7891b18b0a7 X-Migadu-Flow: FLOW_OUT From: Ridong Chen To: Steven Rostedt , Masami Hiramatsu , Andrew Morton , Johannes Weiner Cc: Mathieu Desnoyers , Kairui Song , Qi Zheng , Shakeel Butt , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , Baolin Wang , David Hildenbrand , Michal Hocko , Lorenzo Stoakes , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-mm@kvack.org (open list:MEMORY MANAGEMENT - MGLRU (MULTI-GEN LRU)), Ridong Chen , Ridong Chen Subject: [PATCH 0/3] mm/mglru: add tracepoints for scan and aging paths Date: Fri, 11 Sep 2026 15:28:45 +0800 Message-Id: <20260911072848.2346073-1-ridong.chen@linux.dev> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: D92FAC0002 X-Stat-Signature: cwtxnthd3iw61b3c8ou8trwxhkeozxam X-HE-Tag: 1789111751-364965 X-HE-Meta: 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 y78A9rOz W6XUu5jdoALp3X8rJ3NdcqQJDwPPtvTn+32b5N7h3JKLM820lhASOZrcql/5vtFASqOMHUey4ihgoFv0Y1Zx0dp/OPwj/UhE9bXfS2lBeV9lNqe5KXa/Z9r1Xo2SyYJYmr61UMP52szAPRY63TSD0RkXtD4tmHtZ1P7/372tl5nhCEq0hO7XzM0fJEIsmkECkuYAjQEx/Nys9qgI39R/Ty8GOUrkaAdzSLslfBl1jo+OCVO4M/ZrryyFzoyAbCNm7CFxK Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Ridong Chen 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. 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 | 52 ++++++++++++++--- 2 files changed, 145 insertions(+), 8 deletions(-) -- 2.34.1