From: Kajetan Janiak <kajetan.janiak@gmail.com>
Date: Wed, 18 Nov 2020 10:42:07 +0000 (+0100)
Subject: rgw: disable prefetch in rgw_file
X-Git-Tag: v15.2.16~65^2
X-Git-Url: http://git-server-git.apps.pok.os.sepia.ceph.com/?a=commitdiff_plain;h=refs%2Fpull%2F44170%2Fhead;p=ceph.git

rgw: disable prefetch in rgw_file

Each call to rgw_read (rgw_file.cc) invokes three calls to RGWRados::get_obj_state with s->prefetch_data=true. It results in great read amplification. If length argument in rgw_read call is smaller than rgw_max_chunk_size, then the amplification is threefold.

Signed-off-by: Kajetan Janiak <kjaniak@cloudferro.com>
(cherry picked from commit f915e21e5a1baf6030c1407b3058d4f58c638df9)

Conflicts:
	src/rgw/rgw_op.cc

Cherry-pick notes:
- Octopus sets prfetch data flag through Rados method vs. method on object
---

diff --git a/src/rgw/rgw_file.h b/src/rgw/rgw_file.h
index 32449721ea1..ac8ada0251f 100644
--- a/src/rgw/rgw_file.h
+++ b/src/rgw/rgw_file.h
@@ -2164,6 +2164,8 @@ public:
     return 0;
   }
 
+  bool prefetch_data() override { return false; }
+
 }; /* RGWReadRequest */
 
 /*
diff --git a/src/rgw/rgw_op.cc b/src/rgw/rgw_op.cc
index ec0dbf64361..7dc50a6ce1c 100644
--- a/src/rgw/rgw_op.cc
+++ b/src/rgw/rgw_op.cc
@@ -966,7 +966,7 @@ int RGWGetObj::verify_permission()
 {
   obj = rgw_obj(s->bucket, s->object);
   store->getRados()->set_atomic(s->obj_ctx, obj);
-  if (get_data) {
+  if (prefetch_data()) {
     store->getRados()->set_prefetch_data(s->obj_ctx, obj);
   }