diff --git a/mercurial/configitems.py b/mercurial/configitems.py
--- a/mercurial/configitems.py
+++ b/mercurial/configitems.py
@@ -737,6 +737,14 @@
     b'discovery.grow-sample',
     default=True,
 )
+# When discovery.grow-sample.dynamic is True, the default, the sample size is
+# adapted to the shape of the undecided set (it is set to the max of:
+# <target-size>, len(roots(undecided)), len(heads(undecided)
+coreconfigitem(
+    b'devel',
+    b'discovery.grow-sample.dynamic',
+    default=True,
+)
 # discovery.grow-sample.rate control the rate at which the sample grow
 coreconfigitem(
     b'devel',
diff --git a/mercurial/debugcommands.py b/mercurial/debugcommands.py
--- a/mercurial/debugcommands.py
+++ b/mercurial/debugcommands.py
@@ -1024,6 +1024,12 @@
       If False, the sample size used in set discovery will not be increased
       through the process
 
+    * devel.discovery.grow-sample.dynamic=True
+
+      When discovery.grow-sample.dynamic is True, the default, the sample size is
+      adapted to the shape of the undecided set (it is set to the max of:
+      <target-size>, len(roots(undecided)), len(heads(undecided)
+
     * devel.discovery.grow-sample.rate=1.05
 
       the rate at which the sample grow
diff --git a/mercurial/setdiscovery.py b/mercurial/setdiscovery.py
--- a/mercurial/setdiscovery.py
+++ b/mercurial/setdiscovery.py
@@ -429,12 +429,16 @@
     # full blown discovery
 
     # if the server has a limit to its arguments size, we can't grow the sample.
-    grow_sample = local.ui.configbool(b'devel', b'discovery.grow-sample')
+    configbool = local.ui.configbool
+    grow_sample = configbool(b'devel', b'discovery.grow-sample')
     grow_sample = grow_sample and not remote.limitedarguments
 
+    dynamic_sample = configbool(b'devel', b'discovery.grow-sample.dynamic')
+    hard_limit_sample = not (dynamic_sample or remote.limitedarguments)
+
     randomize = ui.configbool(b'devel', b'discovery.randomize')
     disco = partialdiscovery(
-        local, ownheads, not grow_sample, randomize=randomize
+        local, ownheads, hard_limit_sample, randomize=randomize
     )
     if initial_head_exchange:
         # treat remote heads (and maybe own heads) as a first implicit sample