linux-kernel - Re: [PATCH] mm: vmscan: drop may_writepage and classzone

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Date:   Thu, 14 Mar 2019 11:19:15 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Yafang Shao <laoar.shao@...il.com>
Cc:     vbabka@...e.cz, jrdr.linux@...il.com, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        shaoyafang@...iglobal.com
Subject: Re: [PATCH] mm: vmscan: drop may_writepage and classzone_idx from
 direct reclaim begin template

On Fri 01-03-19 14:24:12, Yafang Shao wrote:
> There are three tracepoints using this template, which are
> mm_vmscan_direct_reclaim_begin,
> mm_vmscan_memcg_reclaim_begin,
> mm_vmscan_memcg_softlimit_reclaim_begin.
> 
> Regarding mm_vmscan_direct_reclaim_begin,
> sc.may_writepage is !laptop_mode, that's a static setting, and
> reclaim_idx is derived from gfp_mask which is already show in this
> tracepoint.
> 
> Regarding mm_vmscan_memcg_reclaim_begin,
> may_writepage is !laptop_mode too, and reclaim_idx is (MAX_NR_ZONES-1),
> which are both static value.
> 
> mm_vmscan_memcg_softlimit_reclaim_begin is the same with
> mm_vmscan_memcg_reclaim_begin.
> 
> So we can drop them all.

I agree. Although classzone_idx is PITA to calculate nothing really
prevents us to have a tool to do that. may_writepage is not all that
useful anymore.

> Signed-off-by: Yafang Shao <laoar.shao@...il.com>

>From a quick glance this looks ok. I haven't really checked deeply or
tried to compile it but the change makes sense.

Acked-by: Michal Hocko <mhocko@...e.com>
> ---
>  include/trace/events/vmscan.h | 26 ++++++++++----------------
>  mm/vmscan.c                   | 14 +++-----------
>  2 files changed, 13 insertions(+), 27 deletions(-)
> 
> diff --git a/include/trace/events/vmscan.h b/include/trace/events/vmscan.h
> index a1cb913..153d90c 100644
> --- a/include/trace/events/vmscan.h
> +++ b/include/trace/events/vmscan.h
> @@ -105,51 +105,45 @@
>  
>  DECLARE_EVENT_CLASS(mm_vmscan_direct_reclaim_begin_template,
>  
> -	TP_PROTO(int order, int may_writepage, gfp_t gfp_flags, int classzone_idx),
> +	TP_PROTO(int order, gfp_t gfp_flags),
>  
> -	TP_ARGS(order, may_writepage, gfp_flags, classzone_idx),
> +	TP_ARGS(order, gfp_flags),
>  
>  	TP_STRUCT__entry(
>  		__field(	int,	order		)
> -		__field(	int,	may_writepage	)
>  		__field(	gfp_t,	gfp_flags	)
> -		__field(	int,	classzone_idx	)
>  	),
>  
>  	TP_fast_assign(
>  		__entry->order		= order;
> -		__entry->may_writepage	= may_writepage;
>  		__entry->gfp_flags	= gfp_flags;
> -		__entry->classzone_idx	= classzone_idx;
>  	),
>  
> -	TP_printk("order=%d may_writepage=%d gfp_flags=%s classzone_idx=%d",
> +	TP_printk("order=%d gfp_flags=%s",
>  		__entry->order,
> -		__entry->may_writepage,
> -		show_gfp_flags(__entry->gfp_flags),
> -		__entry->classzone_idx)
> +		show_gfp_flags(__entry->gfp_flags))
>  );
>  
>  DEFINE_EVENT(mm_vmscan_direct_reclaim_begin_template, mm_vmscan_direct_reclaim_begin,
>  
> -	TP_PROTO(int order, int may_writepage, gfp_t gfp_flags, int classzone_idx),
> +	TP_PROTO(int order, gfp_t gfp_flags),
>  
> -	TP_ARGS(order, may_writepage, gfp_flags, classzone_idx)
> +	TP_ARGS(order, gfp_flags)
>  );
>  
>  #ifdef CONFIG_MEMCG
>  DEFINE_EVENT(mm_vmscan_direct_reclaim_begin_template, mm_vmscan_memcg_reclaim_begin,
>  
> -	TP_PROTO(int order, int may_writepage, gfp_t gfp_flags, int classzone_idx),
> +	TP_PROTO(int order, gfp_t gfp_flags),
>  
> -	TP_ARGS(order, may_writepage, gfp_flags, classzone_idx)
> +	TP_ARGS(order, gfp_flags)
>  );
>  
>  DEFINE_EVENT(mm_vmscan_direct_reclaim_begin_template, mm_vmscan_memcg_softlimit_reclaim_begin,
>  
> -	TP_PROTO(int order, int may_writepage, gfp_t gfp_flags, int classzone_idx),
> +	TP_PROTO(int order, gfp_t gfp_flags),
>  
> -	TP_ARGS(order, may_writepage, gfp_flags, classzone_idx)
> +	TP_ARGS(order, gfp_flags)
>  );
>  #endif /* CONFIG_MEMCG */
>  
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index ac4806f..cdc0305 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -3304,10 +3304,7 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
>  	if (throttle_direct_reclaim(sc.gfp_mask, zonelist, nodemask))
>  		return 1;
>  
> -	trace_mm_vmscan_direct_reclaim_begin(order,
> -				sc.may_writepage,
> -				sc.gfp_mask,
> -				sc.reclaim_idx);
> +	trace_mm_vmscan_direct_reclaim_begin(order, sc.gfp_mask);
>  
>  	nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
>  
> @@ -3338,9 +3335,7 @@ unsigned long mem_cgroup_shrink_node(struct mem_cgroup *memcg,
>  			(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
>  
>  	trace_mm_vmscan_memcg_softlimit_reclaim_begin(sc.order,
> -						      sc.may_writepage,
> -						      sc.gfp_mask,
> -						      sc.reclaim_idx);
> +						      sc.gfp_mask);
>  
>  	/*
>  	 * NOTE: Although we can get the priority field, using it
> @@ -3389,10 +3384,7 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
>  
>  	zonelist = &NODE_DATA(nid)->node_zonelists[ZONELIST_FALLBACK];
>  
> -	trace_mm_vmscan_memcg_reclaim_begin(0,
> -					    sc.may_writepage,
> -					    sc.gfp_mask,
> -					    sc.reclaim_idx);
> +	trace_mm_vmscan_memcg_reclaim_begin(0, sc.gfp_mask);
>  
>  	psi_memstall_enter(&pflags);
>  	noreclaim_flag = memalloc_noreclaim_save();
> -- 
> 1.8.3.1
> 

-- 
Michal Hocko
SUSE Labs