From: Christian Borntraeger Date: Fri, 29 Apr 2022 17:15:26 +0200 Subject: KVM: s390: vsie/gmap: reduce gmap_rmap overhead Git-commit: a06afe8383080c630a7a528b8382fc6bb4925b61 Patch-mainline: v5.18-rc6 References: git-fixes there are cases that trigger a 2nd shadow event for the same vmaddr/raddr combination. (prefix changes, reboots, some known races) This will increase memory usages and it will result in long latencies when cleaning up, e.g. on shutdown. To avoid cases with a list that has hundreds of identical raddrs we check existing entries at insert time. As this measurably reduces the list length this will be faster than traversing the list at shutdown time. In the long run several places will be optimized to create less entries and a shrinker might be necessary. Fixes: 4be130a08420 ("s390/mm: add shadow gmap support") Signed-off-by: Christian Borntraeger Acked-by: David Hildenbrand Link: https://lore.kernel.org/r/20220429151526.1560-1-borntraeger@linux.ibm.com Signed-off-by: Heiko Carstens Acked-by: Petr Tesarik --- arch/s390/mm/gmap.c | 7 +++++++ 1 file changed, 7 insertions(+) --- a/arch/s390/mm/gmap.c +++ b/arch/s390/mm/gmap.c @@ -1181,6 +1181,7 @@ EXPORT_SYMBOL_GPL(gmap_read_table); static inline void gmap_insert_rmap(struct gmap *sg, unsigned long vmaddr, struct gmap_rmap *rmap) { + struct gmap_rmap *temp; void **slot; BUG_ON(!gmap_is_shadow(sg)); @@ -1188,6 +1189,12 @@ static inline void gmap_insert_rmap(stru if (slot) { rmap->next = radix_tree_deref_slot_protected(slot, &sg->guest_table_lock); + for (temp = rmap->next; temp; temp = temp->next) { + if (temp->raddr == rmap->raddr) { + kfree(rmap); + return; + } + } radix_tree_replace_slot(&sg->host_to_rmap, slot, rmap); } else { rmap->next = NULL;