Li Zhijian <lizhijian@xxxxxxxxxxx> writes: > Currently, when a demotion occurs, it will prioritize selecting a node > from the preferred targets as the destination node for the demotion. If > the preferred node does not meet the requirements, it will try from all > the lower memory tier nodes until it finds a suitable demotion destination > node or ultimately fails. > > However, the demotion target information isn't exposed to the users, > especially the preferred target information, which relies on more factors. > This makes users hard to understand the exact demotion behavior. > > Rather than having a new sys interface to expose this information, > printing directly to kernel messages, just like the current page > allocation fallback order does. > > A dmesg example with this patch is as follows: > [ 0.704860] Demotion targets for Node 0: null > [ 0.705456] Demotion targets for Node 1: null > // node 2 is onlined > [ 32.259775] Demotion targets for Node 0: perferred: 2, fallback: 2 > [ 32.261290] Demotion targets for Node 1: perferred: 2, fallback: 2 > [ 32.262726] Demotion targets for Node 2: null > // node 3 is onlined > [ 42.448809] Demotion targets for Node 0: perferred: 2, fallback: 2-3 > [ 42.450704] Demotion targets for Node 1: perferred: 2, fallback: 2-3 > [ 42.452556] Demotion targets for Node 2: perferred: 3, fallback: 3 > [ 42.454136] Demotion targets for Node 3: null > // node 4 is onlined > [ 52.676833] Demotion targets for Node 0: perferred: 2, fallback: 2-4 > [ 52.678735] Demotion targets for Node 1: perferred: 2, fallback: 2-4 > [ 52.680493] Demotion targets for Node 2: perferred: 4, fallback: 3-4 > [ 52.682154] Demotion targets for Node 3: null > [ 52.683405] Demotion targets for Node 4: null > // node 5 is onlined > [ 62.931902] Demotion targets for Node 0: perferred: 2, fallback: 2-5 > [ 62.938266] Demotion targets for Node 1: perferred: 5, fallback: 2-5 > [ 62.943515] Demotion targets for Node 2: perferred: 4, fallback: 3-4 > [ 62.947471] Demotion targets for Node 3: null > [ 62.949908] Demotion targets for Node 4: null > [ 62.952137] Demotion targets for Node 5: perferred: 3, fallback: 3-4 > > CC: "Huang, Ying" <ying.huang@xxxxxxxxx> > CC: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx> > Signed-off-by: Li Zhijian <lizhijian@xxxxxxxxxxx> LGTM, Thanks! Reviewed-by: "Huang, Ying" <ying.huang@xxxxxxxxx> > --- > V2: > Regarding this requirement, we have previously discussed [1]. > The initial proposal involved introducing a new sys interface. > However, due to concerns about potential changes and compatibility > issues with the interface in the future, a consensus was not > reached with the community. Therefore, this time, we are directly > printing out the information. > > [1] https://lore.kernel.org/all/d1d5add8-8f4a-4578-8bf0-2cbe79b09989@xxxxxxxxxxx/ > --- > mm/memory-tiers.c | 24 +++++++++++++++++++++++- > 1 file changed, 23 insertions(+), 1 deletion(-) > > diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c > index 5462d9e3c84c..4d3506a290b7 100644 > --- a/mm/memory-tiers.c > +++ b/mm/memory-tiers.c > @@ -359,6 +359,26 @@ static void disable_all_demotion_targets(void) > synchronize_rcu(); > } > > +static void dump_demotion_targets(void) > +{ > + int node; > + > + for_each_node_state(node, N_MEMORY) { > + struct memory_tier *memtier = __node_get_memory_tier(node); > + nodemask_t preferred = node_demotion[node].preferred; > + > + if (!memtier) > + continue; > + > + if (nodes_empty(preferred)) > + pr_info("Demotion targets for Node %d: null\n", node); > + else > + pr_info("Demotion targets for Node %d: preferred: %*pbl, fallback: %*pbl\n", > + node, nodemask_pr_args(&preferred), > + nodemask_pr_args(&memtier->lower_tier_mask)); > + } > +} > + > /* > * Find an automatic demotion target for all memory > * nodes. Failing here is OK. It might just indicate > @@ -443,7 +463,7 @@ static void establish_demotion_targets(void) > * Now build the lower_tier mask for each node collecting node mask from > * all memory tier below it. This allows us to fallback demotion page > * allocation to a set of nodes that is closer the above selected > - * perferred node. > + * preferred node. > */ > lower_tier = node_states[N_MEMORY]; > list_for_each_entry(memtier, &memory_tiers, list) { > @@ -456,6 +476,8 @@ static void establish_demotion_targets(void) > nodes_andnot(lower_tier, lower_tier, tier_nodes); > memtier->lower_tier_mask = lower_tier; > } > + > + dump_demotion_targets(); > } > > #else
