linux-kernel - Re: [PATCH 2/6] mm/vmscan: use node_is_toptier helper in node

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Date:   Wed, 01 Jun 2022 14:12:22 +0800
From:   Ying Huang <ying.huang@...el.com>
To:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Davidlohr Bueso <dave@...olabs.net>, linux-mm@...ck.org,
        Wei Xu <weixugc@...gle.com>
Cc:     mhocko@...nel.org, akpm@...ux-foundation.org, rientjes@...gle.com,
        yosryahmed@...gle.com, hannes@...xchg.org, shakeelb@...gle.com,
        dave.hansen@...ux.intel.com, tim.c.chen@...ux.intel.com,
        roman.gushchin@...ux.dev, gthelen@...gle.com,
        a.manzanares@...sung.com, heekwon.p@...sung.com,
        gim.jongmin@...sung.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/6] mm/vmscan: use node_is_toptier helper in
 node_reclaim

On Tue, 2022-05-31 at 17:20 +0530, Aneesh Kumar K.V wrote:
> Davidlohr Bueso <dave@...olabs.net> writes:
> 
> > We have helpers for a reason.
> > 
> > Signed-off-by: Davidlohr Bueso <dave@...olabs.net>
> > ---
> >  mm/vmscan.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index 1678802e03e7..cb583fcbf5bf 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -4750,7 +4750,7 @@ int node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
> >  	 * over remote processors and spread off node memory allocations
> >  	 * as wide as possible.
> >  	 */
> > -	if (node_state(pgdat->node_id, N_CPU) && pgdat->node_id != numa_node_id())
> > +	if (node_is_toptier(pgdat->node_id) && pgdat->node_id != numa_node_id())
> >  		return NODE_RECLAIM_NOSCAN;
> >  
> > 
> >  	if (test_and_set_bit(PGDAT_RECLAIM_LOCKED, &pgdat->flags))
> 
> 
> Are we really looking at the top tier in a tiered memory hierarchy here?
> The comment seems to suggest we are looking at local NUMA node?

The code change itself is correct.  But it is an implementation details
that node_is_toptier() == node_state(, N_CPU).  And after we supporting
more memory tiers (like GPU, HBM), we will change the implementation of
node_is_toptier() soon.   So I think that it's better to keep the
original code.

Best Regards,
Huang, Ying