From: Baoquan He <baoquan.he@linux.dev>
To: Ridong Chen <ridong.chen@linux.dev>
Cc: Steven Rostedt <rostedt@goodmis.org>,
Masami Hiramatsu <mhiramat@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Kairui Song <kasong@tencent.com>, Qi Zheng <qi.zheng@linux.dev>,
Shakeel Butt <shakeel.butt@linux.dev>,
Barry Song <baohua@kernel.org>,
Axel Rasmussen <axelrasmussen@google.com>,
Yuanchu Xie <yuanchu@google.com>, Wei Xu <weixugc@google.com>,
Baolin Wang <baolin.wang@linux.alibaba.com>,
David Hildenbrand <david@kernel.org>,
Michal Hocko <mhocko@kernel.org>,
Lorenzo Stoakes <ljs@kernel.org>,
linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org,
"open list:MEMORY MANAGEMENT - MGLRU (MULTI-GEN LRU)"
<linux-mm@kvack.org>, Ridong Chen <chenridong@xiaomi.com>
Subject: Re: [PATCH v2 2/3] mm/mglru: add tracepoint for scan_folios()
Date: Thu, 17 Sep 2026 09:07:54 +0800 [thread overview]
Message-ID: <aqs9auiVq2EplTha@fedora> (raw)
In-Reply-To: <ce8c2ebf-7eb4-4afc-a007-1cfcec439ede@linux.dev>
On 09/16/26 at 08:17pm, Ridong Chen wrote:
>
>
> 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 <chenridong@xiaomi.com>
> > > > ...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
^~~~ typo, s/not/no/
> > 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
Sorry, that's my typo which could cause misunderstanding. I meant "we print
memcg_id but no nid, it may not be so clear". I agree with you that
memcg_id is undispensable.
> scenarios are non-NUMA.
Understood, mobile phone mostly is non-NUMA, while server is different.
About adding nid, I cousulted AI too, it says it's doable.
It says The 12-argument limit only counts the TP_PROTO arguments (that's
the BPF __CAST12/bpf_trace_run12 path), not the __entry fields in
TP_STRUCT__entry. And nid doesn't have to be a 13th argument at all. We
already pass lruvec, so nid can be derived from it in TP_fast_assign with
lruvec_pgdat(lruvec)->node_id.
e.g. for mm_mglru_scan_folios:
TP_STRUCT__entry(
__field(u64, memcg_id)
__field(int, nid)
__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->nid = lruvec_pgdat(lruvec)->node_id;
__entry->highest_zoneidx = highest_zoneidx;
...
),
TP_printk("memcg_id=%llu nid=%d classzone=%d order=%d ...",
__entry->memcg_id,
__entry->nid,
__entry->highest_zoneidx,
...)
lruvec_pgdat() comes from include/linux/mmzone.h, which vmscan.h already
pulls in via linux/mm.h, so no extra include is needed. The same pattern
applies to mm_mglru_inc_max_seq in patch 3 if you want nid there too.
I didn't try it though, please feel free to give it a shot.
Thanks
Baoquan
>
> > >
> > >
> > > > 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
>
next prev parent reply other threads:[~2026-09-17 1:08 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-11 10:29 [PATCH v2 0/3] mm/mglru: add tracepoints for scan and aging paths Ridong Chen
2026-09-11 10:29 ` [PATCH v2 1/3] mm/mglru: factor out lru_gen_seq_nr_pages() Ridong Chen
2026-09-14 7:09 ` Baolin Wang
2026-09-15 6:32 ` Baoquan He
2026-09-11 10:29 ` [PATCH v2 2/3] mm/mglru: add tracepoint for scan_folios() Ridong Chen
2026-09-14 7:47 ` Baolin Wang
2026-09-14 9:04 ` Ridong Chen
2026-09-15 11:14 ` Baoquan He
2026-09-15 12:17 ` Ridong Chen
2026-09-16 2:14 ` Baoquan He
2026-09-16 12:17 ` Ridong Chen
2026-09-17 1:07 ` Baoquan He [this message]
2026-09-17 3:12 ` Ridong Chen
2026-09-16 13:51 ` Steven Rostedt
2026-09-17 1:23 ` Baoquan He
2026-09-17 3:21 ` Ridong Chen
2026-09-11 10:29 ` [PATCH v2 3/3] mm/mglru: add tracepoint for inc_max_seq() Ridong Chen
2026-09-14 7:38 ` Baolin Wang
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=aqs9auiVq2EplTha@fedora \
--to=baoquan.he@linux.dev \
--cc=akpm@linux-foundation.org \
--cc=axelrasmussen@google.com \
--cc=baohua@kernel.org \
--cc=baolin.wang@linux.alibaba.com \
--cc=chenridong@xiaomi.com \
--cc=david@kernel.org \
--cc=hannes@cmpxchg.org \
--cc=kasong@tencent.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linux-trace-kernel@vger.kernel.org \
--cc=ljs@kernel.org \
--cc=mathieu.desnoyers@efficios.com \
--cc=mhiramat@kernel.org \
--cc=mhocko@kernel.org \
--cc=qi.zheng@linux.dev \
--cc=ridong.chen@linux.dev \
--cc=rostedt@goodmis.org \
--cc=shakeel.butt@linux.dev \
--cc=weixugc@google.com \
--cc=yuanchu@google.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox
all inboxes | Powered by JetHome®