osd: fadvise hint WILL_NEED when reading encoded osdmaps

This way will ensure we cache data for recent osdmaps if we need to for
the benefit of laggy clients... even if (in bluestore's case)
bluestore_default_buffered_reads = false (it's true by default).  This
should mitigate any tail latency/work even if the osdmap cache size is too
small.

Signed-off-by: Sage Weil <sage@redhat.com>

diff --git a/src/osd/OSD.cc b/src/osd/OSD.cc
index 795ec29d9a093f3ba434d98eec59721713069bbe..4243893c3a1c6a922978296a7b2a24e8a5339b15 100644 (file)
--- a/src/osd/OSD.cc
+++ b/src/osd/OSD.cc
@@ -1403,7 +1403,8 @@ bool OSDService::_get_map_bl(epoch_t e, bufferlist& bl)
   if (logger)
     logger->inc(l_osd_map_bl_cache_miss);
   found = store->read(coll_t::meta(),
-                     OSD::get_osdmap_pobject_name(e), 0, 0, bl) >= 0;
+                     OSD::get_osdmap_pobject_name(e), 0, 0, bl,
+                     CEPH_OSD_OP_FLAG_FADVISE_WILLNEED) >= 0;
   if (found)
     _add_map_bl(e, bl);
   return found;
@@ -1421,7 +1422,8 @@ bool OSDService::get_inc_map_bl(epoch_t e, bufferlist& bl)
   if (logger)
     logger->inc(l_osd_map_bl_cache_miss);
   found = store->read(coll_t::meta(),
-                     OSD::get_inc_osdmap_pobject_name(e), 0, 0, bl) >= 0;
+                     OSD::get_inc_osdmap_pobject_name(e), 0, 0, bl,
+                     CEPH_OSD_OP_FLAG_FADVISE_WILLNEED) >= 0;
   if (found)
     _add_map_inc_bl(e, bl);
   return found;