linux-kernel - Re: [PATCH v2] mm: vmscan: add tracepoints for node reclaim

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Date:   Fri, 1 Mar 2019 14:08:50 +0530
From:   Souptick Joarder <jrdr.linux@...il.com>
To:     Yafang Shao <laoar.shao@...il.com>
Cc:     Vlastimil Babka <vbabka@...e.cz>, Michal Hocko <mhocko@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux-MM <linux-mm@...ck.org>, linux-kernel@...r.kernel.org,
        shaoyafang@...iglobal.com
Subject: Re: [PATCH v2] mm: vmscan: add tracepoints for node reclaim

On Fri, Mar 1, 2019 at 11:54 AM Yafang Shao <laoar.shao@...il.com> wrote:
>
> In the page alloc fast path, it may do node reclaim, which may cause
> latency spike.
> We should add tracepoint for this event, and also measure the latency
> it causes.
>
> So bellow two tracepoints are introduced,
>         mm_vmscan_node_reclaim_begin
>         mm_vmscan_node_reclaim_end
>
> Signed-off-by: Yafang Shao <laoar.shao@...il.com>

Acked-by: Souptick Joarder <jrdr.linux@...il.com>
(for the comment on v1).

> ---
>  include/trace/events/vmscan.h | 32 ++++++++++++++++++++++++++++++++
>  mm/vmscan.c                   |  6 ++++++
>  2 files changed, 38 insertions(+)
>
> diff --git a/include/trace/events/vmscan.h b/include/trace/events/vmscan.h
> index a1cb913..c1ddf28 100644
> --- a/include/trace/events/vmscan.h
> +++ b/include/trace/events/vmscan.h
> @@ -465,6 +465,38 @@
>                 __entry->ratio,
>                 show_reclaim_flags(__entry->reclaim_flags))
>  );
> +
> +TRACE_EVENT(mm_vmscan_node_reclaim_begin,
> +
> +       TP_PROTO(int nid, int order, gfp_t gfp_flags),
> +
> +       TP_ARGS(nid, order, gfp_flags),
> +
> +       TP_STRUCT__entry(
> +               __field(int, nid)
> +               __field(int, order)
> +               __field(gfp_t, gfp_flags)
> +       ),
> +
> +       TP_fast_assign(
> +               __entry->nid = nid;
> +               __entry->order = order;
> +               __entry->gfp_flags = gfp_flags;
> +       ),
> +
> +       TP_printk("nid=%d order=%d gfp_flags=%s",
> +               __entry->nid,
> +               __entry->order,
> +               show_gfp_flags(__entry->gfp_flags))
> +);
> +
> +DEFINE_EVENT(mm_vmscan_direct_reclaim_end_template, mm_vmscan_node_reclaim_end,
> +
> +       TP_PROTO(unsigned long nr_reclaimed),
> +
> +       TP_ARGS(nr_reclaimed)
> +);
> +
>  #endif /* _TRACE_VMSCAN_H */
>
>  /* This part must be outside protection */
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index ac4806f..2bee5d1 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -4241,6 +4241,9 @@ static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned in
>                 .reclaim_idx = gfp_zone(gfp_mask),
>         };
>
> +       trace_mm_vmscan_node_reclaim_begin(pgdat->node_id, order,
> +                                          sc.gfp_mask);
> +
>         cond_resched();
>         fs_reclaim_acquire(sc.gfp_mask);
>         /*
> @@ -4267,6 +4270,9 @@ static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned in
>         current->flags &= ~PF_SWAPWRITE;
>         memalloc_noreclaim_restore(noreclaim_flag);
>         fs_reclaim_release(sc.gfp_mask);
> +
> +       trace_mm_vmscan_node_reclaim_end(sc.nr_reclaimed);
> +
>         return sc.nr_reclaimed >= nr_pages;
>  }
>
> --
> 1.8.3.1
>