On Fri, Feb 16, 2024 at 08:40:45PM +0900, Byungchul Park wrote: > From 150af2f78e19217a1d03e47e3ee5279684590fb4 Mon Sep 17 00:00:00 2001 > From: Byungchul Park <byungchul@xxxxxx> > Date: Fri, 16 Feb 2024 20:18:10 +0900 > Subject: [PATCH v3] sched/numa, mm: do not promote folios to nodes not set N_MEMORY "do not try to promote folios to memoryless nodes" 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 <byungchul@xxxxxx> > --- > 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
