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    SubjectRe: [PATCH 3/3] Add name fields in shrinker tracepoint definitions
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    On 07/09/2016 11:05 AM, Janani Ravichandran wrote:
    > Currently, the mm_shrink_slab_start and mm_shrink_slab_end
    > tracepoints tell us how much time was spent in a shrinker, the number of
    > objects scanned, etc. But there is no information about the identity of
    > the shrinker. This patch enables the trace output to display names of
    > shrinkers.
    >
    > ---
    > include/trace/events/vmscan.h | 10 ++++++++--
    > 1 file changed, 8 insertions(+), 2 deletions(-)
    >
    > diff --git a/include/trace/events/vmscan.h b/include/trace/events/vmscan.h
    > index 0101ef3..be4c5b0 100644
    > --- a/include/trace/events/vmscan.h
    > +++ b/include/trace/events/vmscan.h
    > @@ -189,6 +189,7 @@ TRACE_EVENT(mm_shrink_slab_start,
    > cache_items, delta, total_scan),
    >
    > TP_STRUCT__entry(
    > + __field(char *, name)
    > __field(struct shrinker *, shr)
    > __field(void *, shrink)
    > __field(int, nid)
    > @@ -202,6 +203,7 @@ TRACE_EVENT(mm_shrink_slab_start,
    > ),
    >
    > TP_fast_assign(
    > + __entry->name = shr->name;
    > __entry->shr = shr;
    > __entry->shrink = shr->scan_objects;
    > __entry->nid = sc->nid;
    > @@ -214,7 +216,8 @@ TRACE_EVENT(mm_shrink_slab_start,
    > __entry->total_scan = total_scan;
    > ),
    >
    > - TP_printk("%pF %p: nid: %d objects to shrink %ld gfp_flags %s pgs_scanned %ld lru_pgs %ld cache items %ld delta %lld total_scan %ld",
    > + TP_printk("name: %s %pF %p: nid: %d objects to shrink %ld gfp_flags %s pgs_scanned %ld lru_pgs %ld cache items %ld delta %lld total_scan %ld",
    > + __entry->name,

    Is this legal to do when printing is not done via the /sys ... file
    itself, but raw data is collected and then printed by e.g. trace-cmd?
    How can it possibly interpret the "char *" kernel pointer?

    > __entry->shrink,
    > __entry->shr,
    > __entry->nid,
    > @@ -235,6 +238,7 @@ TRACE_EVENT(mm_shrink_slab_end,
    > total_scan),
    >
    > TP_STRUCT__entry(
    > + __field(char *, name)
    > __field(struct shrinker *, shr)
    > __field(int, nid)
    > __field(void *, shrink)
    > @@ -245,6 +249,7 @@ TRACE_EVENT(mm_shrink_slab_end,
    > ),
    >
    > TP_fast_assign(
    > + __entry->name = shr->name;
    > __entry->shr = shr;
    > __entry->nid = nid;
    > __entry->shrink = shr->scan_objects;
    > @@ -254,7 +259,8 @@ TRACE_EVENT(mm_shrink_slab_end,
    > __entry->total_scan = total_scan;
    > ),
    >
    > - TP_printk("%pF %p: nid: %d unused scan count %ld new scan count %ld total_scan %ld last shrinker return val %d",
    > + TP_printk("name: %s %pF %p: nid: %d unused scan count %ld new scan count %ld total_scan %ld last shrinker return val %d",
    > + __entry->name,
    > __entry->shrink,
    > __entry->shr,
    > __entry->nid,
    >

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