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Date:   Wed, 1 Jun 2022 07:00:41 -0700
From:   Davidlohr Bueso <dave@stgolabs.net>
To:     Ying Huang <ying.huang@intel.com>
Cc:     "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
        linux-mm@kvack.org, Wei Xu <weixugc@google.com>, mhocko@kernel.org,
        akpm@linux-foundation.org, rientjes@google.com,
        yosryahmed@google.com, hannes@cmpxchg.org, shakeelb@google.com,
        dave.hansen@linux.intel.com, tim.c.chen@linux.intel.com,
        roman.gushchin@linux.dev, gthelen@google.com,
        a.manzanares@samsung.com, heekwon.p@samsung.com,
        gim.jongmin@samsung.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/6] mm/vmscan: use node_is_toptier helper in node_reclaim
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        a.manzanares@samsung.com, heekwon.p@samsung.com,
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On Wed, 01 Jun 2022, Ying Huang wrote:

>On Tue, 2022-05-31 at 17:20 +0530, Aneesh Kumar K.V wrote:
>> Davidlohr Bueso <dave@stgolabs.net> writes:
>>
>> > We have helpers for a reason.
>> >
>> > Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
>> > ---
>> > =A0mm/vmscan.c | 2 +-
>> > =A01 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)
>> > =A0	 * over remote processors and spread off node memory allocations
>> > =A0	 * as wide as possible.
>> > =A0	 */
>> > -	if (node_state(pgdat->node_id, N_CPU) && pgdat->node_id !=3D numa_no=
de_id())
>> > +	if (node_is_toptier(pgdat->node_id) && pgdat->node_id !=3D numa_node=
_id())
>> > =A0		return NODE_RECLAIM_NOSCAN;
>> >
>> >
>> > =A0	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() =3D=3D 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.

Agreed.

Thanks,
Davidlohr