[PATCH v2] powerpc/drmem: Don't compute the NUMA node for each LMB

[Laurent Dufour]

All the LMB from the same set of ibm,dynamic-memory-v2 property are
sharing the same NUMA node. Don't compute that node for each one.

Tested on a system with 1022 LMBs spread on 4 NUMA nodes, only 4 calls to
lmb_set_nid() have been made instead of 1022.

This should prevent some soft lockups when starting large guests

Code has meaning only if CONFIG_MEMORY_HOTPLUG is set, otherwise the nid
field is not present in the drmem_lmb structure.

Signed-off-by: Laurent Dufour <lduf...@linux.ibm.com>
---
 arch/powerpc/mm/drmem.c | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/mm/drmem.c b/arch/powerpc/mm/drmem.c
index b2eeea39684c..c11b6ec99ea3 100644
--- a/arch/powerpc/mm/drmem.c
+++ b/arch/powerpc/mm/drmem.c
@@ -402,6 +402,9 @@ static void __init init_drmem_v2_lmbs(const __be32 *prop)
        const __be32 *p;
        u32 i, j, lmb_sets;
        int lmb_index;
+#ifdef CONFIG_MEMORY_HOTPLUG
+       struct drmem_lmb *first = NULL;
+#endif
 
        lmb_sets = of_read_number(prop++, 1);
        if (lmb_sets == 0)
@@ -426,6 +429,15 @@ static void __init init_drmem_v2_lmbs(const __be32 *prop)
        for (i = 0; i < lmb_sets; i++) {
                read_drconf_v2_cell(&dr_cell, &p);
 
+#ifdef CONFIG_MEMORY_HOTPLUG
+               /*
+                * Fetch the NUMA node id for the fist set or if the
+                * associativity index is different from the previous set.
+                */
+               if (first && dr_cell.aa_index != first->aa_index)
+                       first = NULL;
+#endif
+
                for (j = 0; j < dr_cell.seq_lmbs; j++) {
                        lmb = &drmem_info->lmbs[lmb_index++];
 
@@ -438,7 +450,18 @@ static void __init init_drmem_v2_lmbs(const __be32 *prop)
                        lmb->aa_index = dr_cell.aa_index;
                        lmb->flags = dr_cell.flags;
 
-                       lmb_set_nid(lmb);
+#ifdef CONFIG_MEMORY_HOTPLUG
+                       /*
+                        * All the LMB in the set share the same NUMA
+                        * associativity property. So read that node only once.
+                        */
+                       if (!first) {
+                               lmb_set_nid(lmb);
+                               first = lmb;
+                       } else {
+                               lmb->nid = first->nid;
+                       }
+#endif
                }
        }
 }
-- 
2.28.0