* Re: [PATCH v4 1/5] mm/rmap: add tracepoint for rmap_walk
[not found] <20260503203911259NKHEr5gDy3PbvnSc077a7@zte.com.cn>
@ 2026-05-13 12:03 ` David Hildenbrand (Arm)
0 siblings, 0 replies; only message in thread
From: David Hildenbrand (Arm) @ 2026-05-13 12:03 UTC (permalink / raw)
To: xu.xin16, akpm, ljs; +Cc: hughd, linux-mm, linux-kernel, michel
On 5/3/26 14:39, xu.xin16@zte.com.cn wrote:
> From: xu xin <xu.xin16@zte.com.cn>
>
> Add a new tracepoint rmap_walk in mm/rmap.c to monitor reverse mapping
> traversal. The tracepoint records the duration (in nanoseconds), the
> type of the folio (KSM, anonymous, or file-backed), and the addresses
> of the folio and rmap_walk_control structures. The type determination
> is performed inside the tracepoint to keep the function itself
> lightweight.
>
> '# cat /sys/kernel/tracing/trace
> '# tracer: nop
> '#
> '# entries-in-buffer/entries-written: 408/408 #P:4
> '#
> '# _-----=> irqs-off/BH-disabled
> '# / _----=> need-resched
> '# | / _---=> hardirq/softirq
> '# || / _--=> preempt-depth
> '# ||| / _-=> migrate-disable
> '# |||| / delay
> '#TASK-PID CPU# ||||| TIMESTAMP FUNCTION
> '# | | | ||||| | |
> rmap-215 [001] ..... 692.237079: rmap_walk: folio=000000000029ddcb rwc=00000000dac4cda0 duration_ns=828682 page_type=ksm locked=false
> rmap-215 [001] ..... 692.239480: rmap_walk: folio=0000000092a21fd3 rwc=00000000986376ff duration_ns=905966 page_type=ksm locked=false
> rmap-230 [003] ..... 692.583619: rmap_walk: folio=0000000037a237b6 rwc=0000000080fbbb0a duration_ns=107892 page_type=ksm locked=false
> rmap-230 [003] ..... 692.584104: rmap_walk: folio=0000000031bdbf8b rwc=00000000b39c973a duration_ns=330886 page_type=ksm locked=false
> rmap-244 [003] ..... 692.708706: rmap_walk: folio=000000009105fa6b rwc=0000000037d46cd7 duration_ns=987826 page_type=file locked=false
> rmap-244 [003] ..... 692.709198: rmap_walk: folio=000000009105fa6b rwc=0000000093942e2c duration_ns=161733 page_type=file locked=false
> rmap-244 [003] ..... 692.709606: rmap_walk: folio=000000009105fa6b rwc=0000000037d46cd7 duration_ns=54428 page_type=file locked=false
> rmap-244 [003] ..... 692.709658: rmap_walk: folio=000000009105fa6b rwc=0000000093942e2c duration_ns=27192 page_type=file locked=false
>
> Signed-off-by: xu xin <xu.xin16@zte.com.cn>
> ---
> include/trace/events/rmap.h | 49 +++++++++++++++++++++++++++++++++++++
> mm/rmap.c | 14 +++++++++++
> 2 files changed, 63 insertions(+)
> create mode 100644 include/trace/events/rmap.h
>
> diff --git a/include/trace/events/rmap.h b/include/trace/events/rmap.h
> new file mode 100644
> index 000000000000..987fa204d65d
> --- /dev/null
> +++ b/include/trace/events/rmap.h
> @@ -0,0 +1,49 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#undef TRACE_SYSTEM
> +#define TRACE_SYSTEM rmap
> +
> +#if !defined(_TRACE_RMAP_H) || defined(TRACE_HEADER_MULTI_READ)
> +#define _TRACE_RMAP_H
> +
> +#include <linux/tracepoint.h>
> +#include <linux/rmap.h>
> +
> +#define GET_RMAP_PAGE_TYPE(folio) (folio_test_ksm(folio) ? "ksm" : \
> + (folio_test_anon(folio) ? "anon" : "file"))
> +
> +TRACE_EVENT(rmap_walk,
> +
> + TP_PROTO(struct folio *folio, struct rmap_walk_control *rwc, u64 duration_ns, bool locked),
> +
> + TP_ARGS(folio, rwc, duration_ns, locked),
> +
> + TP_STRUCT__entry(
> + __field(unsigned long, folio_addr)
> + __field(unsigned long, rwc_addr)
> + __field(u64, duration_ns)
> + __string(page_type, GET_RMAP_PAGE_TYPE(folio))
> + __field(bool, locked)
> + ),
> +
> + TP_fast_assign(
> + __entry->folio_addr = (unsigned long)folio;
> + __entry->rwc_addr = (unsigned long)rwc;
> + __entry->duration_ns = duration_ns;
> + __assign_str(page_type);
> + __entry->locked = locked;
> + ),
> +
> + TP_printk("folio=%p rwc=%p duration_ns=%llu page_type=%s locked=%s",
> + (void *)(unsigned long)__entry->folio_addr,
> + (void *)(unsigned long)__entry->rwc_addr,
> + __entry->duration_ns,
> + __get_str(page_type),
> + __entry->locked ? "true" : "false")
> +);
> +
> +
> +
> +#endif /* _TRACE_RMAP_H */
> +
> +/* This part must be outside protection */
> +#include <trace/define_trace.h>
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 78b7fb5f367c..14bf8483f38b 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -75,11 +75,13 @@
> #include <linux/userfaultfd_k.h>
> #include <linux/mm_inline.h>
> #include <linux/oom.h>
> +#include <linux/sched/clock.h>
>
> #include <asm/tlb.h>
>
> #define CREATE_TRACE_POINTS
> #include <trace/events/migrate.h>
> +#include <trace/events/rmap.h>
>
> #include "internal.h"
> #include "swap.h"
> @@ -3098,23 +3100,35 @@ static void rmap_walk_file(struct folio *folio,
>
> void rmap_walk(struct folio *folio, struct rmap_walk_control *rwc)
> {
> + u64 ts_start, delta_ns;
> + ts_start = local_clock();
> +
> if (unlikely(folio_test_ksm(folio)))
> rmap_walk_ksm(folio, rwc);
> else if (folio_test_anon(folio))
> rmap_walk_anon(folio, rwc, false);
> else
> rmap_walk_file(folio, rwc, false);
> +
> + delta_ns = local_clock() - ts_start;
> + trace_rmap_walk(folio, rwc, delta_ns, false);
> }
>
> /* Like rmap_walk, but caller holds relevant rmap lock */
> void rmap_walk_locked(struct folio *folio, struct rmap_walk_control *rwc)
> {
> + u64 ts_start, delta_ns;
> + ts_start = local_clock();
> +
> /* no ksm support for now */
> VM_BUG_ON_FOLIO(folio_test_ksm(folio), folio);
> if (folio_test_anon(folio))
> rmap_walk_anon(folio, rwc, true);
> else
> rmap_walk_file(folio, rwc, true);
> +
> + delta_ns = local_clock() - ts_start;
> + trace_rmap_walk(folio, rwc, delta_ns, true);
> }
>
> #ifdef CONFIG_HUGETLB_PAGE
Doing the clock stuff manually is nasty.
We could have a trace_rmap_walk_start() + trace_rmap_walk_stop().
But I wonder right now, whether we really need that information in the tree?
For local debugging (what you did) having this OOT patch is probably fine.
--
Cheers,
David
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