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imf02.hostedemail.com; dkim=none; dmarc=none; spf=pass (imf02.hostedemail.com: domain of byungchul@sk.com designates 166.125.252.92 as permitted sender) smtp.mailfrom=byungchul@sk.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1708308634; a=rsa-sha256; cv=none; b=zPD6ZmwyNyPIS7CsPkY5EtO+Mk/4UuVViUToXrutSvtT9ISFssnrGzpQRdIzw8fisG76re I2wqmPaaHFX/mN+PYwfr4vGZXs+YyF+S8UmXPMbySGdxrfb+E3q8RgzUQBV09ahvvYLXUz 6ToiTfxIILWR1jXMNYT3Yohb48eAM60= X-AuditID: a67dfc5b-d6dff70000001748-84-65d2b8979e0c Date: Mon, 19 Feb 2024 11:10:26 +0900 From: Byungchul Park To: Oscar Salvador Cc: mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel_team@skhynix.com, akpm@linux-foundation.org Subject: Re: [PATCH v3] sched/numa, mm: do not promote folios to nodes not set N_MEMORY Message-ID: <20240219021026.GB65758@system.software.com> References: <20240216114045.24828-1-byungchul@sk.com> MIME-Version: 1.0 Content-Type: text/plain; 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Thank you. I will. > As this is not a bug fix but an optimization, as we will fail anyways > in migrate_misplaced_folio() when migrate_balanced_pgdat() notices that > we do not have any memory on that code. > > With the other comments addressed: > > Reviewed-by: Oscar Salvador Thank you for reviewing. Byungchul > > because AFAICS we are just trying. > > Even if should_numa_migrate_memory() returns true, I assume that we will > > fail somewhere down the chain e.g: migrate_pages() when we see that this > > node does not any memory, right? > > > > > A numa node might not have its local memory but CPUs. Promoting a folio > > > to the node's local memory is nonsense. So avoid nodes not set N_MEMORY > > > from getting promoted. > > > > If you talk about memoryless nodes everybody gets it better IMHO. > > "Memoryless nodes do not have any memory to migrate to, so stop trying it." > > > > > > > Signed-off-by: Byungchul Park > > > --- > > > kernel/sched/fair.c | 7 +++++++ > > > 1 file changed, 7 insertions(+) > > > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > > index d7a3c63a2171..7ed9ef3c0134 100644 > > > --- a/kernel/sched/fair.c > > > +++ b/kernel/sched/fair.c > > > @@ -1828,6 +1828,13 @@ bool should_numa_migrate_memory(struct task_struct *p, struct folio *folio, > > > int dst_nid = cpu_to_node(dst_cpu); > > > int last_cpupid, this_cpupid; > > > > > > + /* > > > + * A node of dst_nid might not have its local memory. Promoting > > > + * a folio to the node is meaningless. > > > + */ > > > + if (!node_state(dst_nid, N_MEMORY)) > > > + return false; > > > > "Cannot migrate to memoryless nodes" > > > > seems shorter and more clear. > > > > So, what happens when we return true here? will we fail at > > migrate_pages() I guess? That is quite down the road so I guess > > this check can save us some time. > > > > > > -- > > Oscar Salvador > > SUSE Labs > > > > -- > Oscar Salvador > SUSE Labs