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Wed, 16 Sep 2026 12:17:57 +0000 X-Mizu-Trace-ID: 6aeebd5c5ba43b2f X-Migadu-Flow: FLOW_OUT Message-ID: Date: Wed, 16 Sep 2026 20:17:50 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/3] mm/mglru: add tracepoint for scan_folios() To: Baoquan He Cc: Steven Rostedt , Masami Hiramatsu , Andrew Morton , Johannes Weiner , Mathieu Desnoyers , Kairui Song , Qi Zheng , Shakeel Butt , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baolin Wang , David Hildenbrand , Michal Hocko , Lorenzo Stoakes , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, "open list:MEMORY MANAGEMENT - MGLRU (MULTI-GEN LRU)" , Ridong Chen References: <20260911102939.2485750-1-ridong.chen@linux.dev> <20260911102939.2485750-3-ridong.chen@linux.dev> From: Ridong Chen In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 5B07D40009 X-Stat-Signature: xbqpnahkapmhhqqpjx41teox88e1zgr6 X-HE-Tag: 1789561079-692017 X-HE-Meta: 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 382luD9s PTcltE7P9D6wr+cq280OkjTXHkzib/cf2nvcvn1vT3vuTLzKYWK+FGcuo/Ri0y2y2SlWQTCUoJCjEri3SLv8JQ8liF13aWVVTp6FEHx0RzvOFJOntCC/V6zojxrg4GZRHZBdjqWDgG9bL8hilGyfNBcSbiDPYbdZwBoO/Wbd6b9DSzOJDLADwDxLebCQ+tFdXW6QHibiteoaZabmOFm8N+ZJTxbSwGkLAKztblmt5YZJMXFkhQCR2jz5YNtbOwfZySVEZvYzxeP9RKqOYiIirciDJk4+nVvMh/VjWYp0UI/qZBUt1OJ3RqshlpH1HbjGaIlFlYHeHfOy9ofK9+Lnl4dUPiGijMGVbPyE1 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/16/2026 10:14 AM, Baoquan He wrote: > On 09/15/26 at 08:17pm, Ridong Chen wrote: >> >> >> On 9/15/2026 7:14 PM, Baoquan He wrote: >>> On 09/11/26 at 06:29pm, Ridong Chen wrote: >>>> From: Ridong Chen >>> ...snip... >>>> --- >>>> include/trace/events/vmscan.h | 63 +++++++++++++++++++++++++++++++++++ >>>> mm/vmscan.c | 6 ++++ >>>> 2 files changed, 69 insertions(+) >>>> >>>> diff --git a/include/trace/events/vmscan.h b/include/trace/events/vmscan.h >>>> index 8a872990b4be..5defa8f6719c 100644 >>>> --- a/include/trace/events/vmscan.h >>>> +++ b/include/trace/events/vmscan.h >>>> @@ -392,6 +392,69 @@ TRACE_EVENT(mm_vmscan_lru_isolate, >>>> __print_symbolic(__entry->lru, LRU_NAMES)) >>>> ); >>>> +TRACE_EVENT(mm_mglru_scan_folios, >>>> + >>>> + TP_PROTO(struct lruvec *lruvec, >>>> + int highest_zoneidx, >>>> + int order, >>>> + unsigned long nr_requested, >>>> + unsigned long nr_scanned, >>>> + unsigned long nr_sorted, >>>> + unsigned long nr_skipped, >>>> + unsigned long nr_taken, >>>> + int lru, >>>> + unsigned long max_seq, >>>> + int tier, >>>> + unsigned long min_seq), >>> >> >> Thank you for your review. >> >>> Do we need show nid? Guess phone vendor doesn't care about multi-NUMA >>> system. >>> >> >> Eh, nid is not an mglru-specific key. Since there are 12 elements here, it >> can't be added here. > > Hmm, we print memcg_id but not nid, it may not be so clear. How do you > differentiate several lruvec-s on one memcg? I am not very familiar with > trace mechanism, do we have a element number limit? > Yes, it will fail to compile if there are more than 12 elements. With AI's help, see include/trace/bpf_probe.h ``` 30 #define __CAST1(a,...) __CAST_TO_U64(a) 31 #define __CAST2(a,...) __CAST_TO_U64(a), __CAST1(__VA_ARGS__) 32 #define __CAST3(a,...) __CAST_TO_U64(a), __CAST2(__VA_ARGS__) 33 #define __CAST4(a,...) __CAST_TO_U64(a), __CAST3(__VA_ARGS__) 34 #define __CAST5(a,...) __CAST_TO_U64(a), __CAST4(__VA_ARGS__) 35 #define __CAST6(a,...) __CAST_TO_U64(a), __CAST5(__VA_ARGS__) 36 #define __CAST7(a,...) __CAST_TO_U64(a), __CAST6(__VA_ARGS__) 37 #define __CAST8(a,...) __CAST_TO_U64(a), __CAST7(__VA_ARGS__) 38 #define __CAST9(a,...) __CAST_TO_U64(a), __CAST8(__VA_ARGS__) 39 #define __CAST10(a,...) __CAST_TO_U64(a), __CAST9(__VA_ARGS__) 40 #define __CAST11(a,...) __CAST_TO_U64(a), __CAST10(__VA_ARGS__) 41 #define __CAST12(a,...) __CAST_TO_U64(a), __CAST11(__VA_ARGS__) /* tracepoints with more than 12 arguments will hit build error */ ``` > Imagine I only want to trace this function, now I can see memcg_id, > zone_idex, while don't know node/lruvec, that's a little pitty. Just my > personal opinion, I could miss anything. > Yeah, you are right. In my personal experience, I always enable trace_mm_vmscan_lru_isolate and trace_mm_vmscan_lru_shrink_inactive, which contain node_id. So we can see how the lruvec is scanned and shrunk, and we can get node_id from trace_mm_vmscan_lru_shrink_inactive. I am not arguing that this is exactly the 'correct' way to use these tracepoints, but I think it is a common usage. I am open to that. If we want to record node_id, we have to remove an element. Maybe tier? But I would strongly recommend record memcg_id, we frequently need to check the reclaim behavior of a memcg, and most of our scenarios are non-NUMA. >> >> >>> And I checked v1 thread, seems Steven suggested to move the two int to >>> avoid extra padding. >>> >> >> Yeah, I will update it. I updated v2 to fix Sashiko's issue, before Steven >> had any comment. >> >> >>>> + >>>> + TP_ARGS(lruvec, highest_zoneidx, order, nr_requested, nr_scanned, >>>> + nr_sorted, nr_skipped, nr_taken, lru, max_seq, tier, min_seq), >>>> + >>>> + TP_STRUCT__entry( >>>> + __field(u64, memcg_id) >>>> + __field(int, highest_zoneidx) >>>> + __field(int, order) >>>> + __field(unsigned long, nr_requested) >>>> + __field(unsigned long, nr_scanned) >>>> + __field(unsigned long, nr_sorted) >>>> + __field(unsigned long, nr_skipped) >>>> + __field(unsigned long, nr_taken) >>>> + __field(int, lru) >>>> + __field(unsigned long, max_seq) >>>> + __field(int, tier) >>>> + __field(unsigned long, min_seq) >>>> + ), >>>> + >>>> + TP_fast_assign( >>>> + __entry->memcg_id = mem_cgroup_id(lruvec_memcg(lruvec)); >>>> + __entry->highest_zoneidx = highest_zoneidx; >>>> + __entry->order = order; >>>> + __entry->nr_requested = nr_requested; >>>> + __entry->nr_scanned = nr_scanned; >>>> + __entry->nr_sorted = nr_sorted; >>>> + __entry->nr_skipped = nr_skipped; >>>> + __entry->nr_taken = nr_taken; >>>> + __entry->lru = lru; >>>> + __entry->max_seq = max_seq; >>>> + __entry->tier = tier; >>>> + __entry->min_seq = min_seq; >>>> + ), >>>> + >>>> + TP_printk("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", >>>> + __entry->memcg_id, >>>> + __entry->highest_zoneidx, >>>> + __entry->order, >>>> + __entry->nr_requested, >>>> + __entry->nr_scanned, >>>> + __entry->nr_sorted, >>>> + __entry->nr_skipped, >>>> + __entry->nr_taken, >>>> + __print_symbolic(__entry->lru, LRU_NAMES), >>>> + __entry->max_seq, >>>> + __entry->tier, >>>> + __entry->min_seq) >>>> +); >>>> + >>>> TRACE_EVENT(mm_vmscan_write_folio, >>>> TP_PROTO(struct folio *folio), >>>> diff --git a/mm/vmscan.c b/mm/vmscan.c >>>> index 2554a6513aa8..67f59aa73fb9 100644 >>>> --- a/mm/vmscan.c >>>> +++ b/mm/vmscan.c >>>> @@ -4876,6 +4876,12 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec, >>>> trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, nr_to_scan, >>>> scanned, skipped, isolated, >>>> type ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON); >>>> + trace_mm_mglru_scan_folios(lruvec, >>>> + sc->reclaim_idx, sc->order, nr_to_scan, >>>> + scanned, sorted, skipped, isolated, >>>> + type ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON, >>>> + lrugen->max_seq, tier, >>>> + lrugen->min_seq[type]); >>> >>> And seems Steven also suggested to calculate lru, max_seq, min_seq in >>> TP_fast_assign() in v1 which could be missed. >>> >> >> Thanks, I will update it following Steven's suggestions. >> >> >>> TP_fast_assign( >>> __entry->memcg_id = mem_cgroup_id(lruvec_memcg(lruvec)); >>> __entry->highest_zoneidx = sc->reclaim_idx; >>> __entry->order = sc->order; >>> __entry->nr_requested = nr_requested; >>> __entry->nr_scanned = nr_scanned; >>> __entry->nr_sorted = nr_sorted; >>> __entry->nr_skipped = nr_skipped; >>> __entry->nr_taken = nr_taken; >>> __entry->lru = type ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON; >>> __entry->max_seq = lrugen->max_seq; >>> __entry->tier = tier; >>> __entry->min_seq = lrugen->min_seq; >>> ), >>> >> >> However, 'sc' is an internal structure, so sc->order cannot be accessed in >> TP_fast_assign(), and I don't think it is worth making scan_control an >> external structure just for this. > > Agree. > >> >>> >>>> *isolatedp = isolated; >>>> return scanned; >>>> -- >>>> 2.34.1 >>>> >> >> -- >> Best regards >> Ridong >> -- Best regards Ridong