librbd: remove limit on number of objects in the cache

The number of objects is not a significant indicated of when data
should be written out for rbd. Use the highest possible value for
number of objects and just rely on the dirty data limits to trigger
flushing. When the number of objects is low, and many start being
flushed before they accumulate many requests, it hurts average request
size and performance for many concurrent sequential writes.

Fixes: #7385
Backport: emperor, dumpling
Signed-off-by: Josh Durgin <josh.durgin@inktank.com>
(cherry picked from commit 0559d31db29ea83bdb6cec72b830d16b44e3cd35)

diff --git a/src/librbd/ImageCtx.cc b/src/librbd/ImageCtx.cc
index 41518b67698cdec5a750141703d574a523686e7d..77cb8503ad63f807bb875cd6b658692249eb7853 100644 (file)
--- a/src/librbd/ImageCtx.cc
+++ b/src/librbd/ImageCtx.cc
@@ -86,7 +86,7 @@ namespace librbd {
       object_cacher = new ObjectCacher(cct, pname, *writeback_handler, cache_lock,
                                       NULL, NULL,
                                       cct->_conf->rbd_cache_size,
-                                      10,  /* reset this in init */
+                                      (uint64_t) -1, // unlimited number of objects
                                       init_max_dirty,
                                       cct->_conf->rbd_cache_target_dirty,
                                       cct->_conf->rbd_cache_max_dirty_age,
@@ -182,14 +182,6 @@ namespace librbd {
       snprintf(format_string, len, "%s.%%016llx", object_prefix.c_str());
     }
 
-    // size object cache appropriately
-    if (object_cacher) {
-      uint64_t obj = cct->_conf->rbd_cache_size / (1ull << order);
-      ldout(cct, 10) << " cache bytes " << cct->_conf->rbd_cache_size << " order " << (int)order
-                    << " -> about " << obj << " objects" << dendl;
-      object_cacher->set_max_objects(obj * 4 + 10);
-    }
-
     ldout(cct, 10) << "init_layout stripe_unit " << stripe_unit
                   << " stripe_count " << stripe_count
                   << " object_size " << layout.fl_object_size