From 1e84b46c3f9d4750e6f5facbd166fcbb33c7dc39 Mon Sep 17 00:00:00 2001
From: Alexander Boettcher <alexander.boettcher@genode-labs.com>
Date: Tue, 9 Feb 2021 23:06:16 +0100
Subject: [PATCH] slab: add option to free empty blocks

explictly by a method

Issue #4014
---
 repos/base/include/base/allocator_avl.h |  6 +++++-
 repos/base/include/base/slab.h          |  6 ++++++
 repos/base/lib/symbols/ld               |  1 +
 repos/base/src/lib/base/slab.cc         | 11 +++++++++++
 4 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/repos/base/include/base/allocator_avl.h b/repos/base/include/base/allocator_avl.h
index 9e24e67125..9accdfc27e 100644
--- a/repos/base/include/base/allocator_avl.h
+++ b/repos/base/include/base/allocator_avl.h
@@ -340,7 +340,11 @@ class Genode::Allocator_avl_tpl : public Allocator_avl_base
 			_metadata((metadata_chunk_alloc) ? metadata_chunk_alloc : this,
 			          (Block *)&_initial_md_block) { }
 
-		~Allocator_avl_tpl() { _revert_allocations_and_ranges(); }
+		~Allocator_avl_tpl()
+		{
+			_metadata.free_empty_blocks();
+			_revert_allocations_and_ranges();
+		}
 
 		/**
 		 * Return size of slab blocks used for meta data
diff --git a/repos/base/include/base/slab.h b/repos/base/include/base/slab.h
index e2beffb5c6..3cc477af9e 100644
--- a/repos/base/include/base/slab.h
+++ b/repos/base/include/base/slab.h
@@ -138,6 +138,12 @@ class Genode::Slab : public Allocator
 		Allocator *backing_store() { return _backing_store; }
 
 
+		/**
+		 * Free memory of empty slab blocks
+		 */
+		void free_empty_blocks();
+
+
 		/*************************
 		 ** Allocator interface **
 		 *************************/
diff --git a/repos/base/lib/symbols/ld b/repos/base/lib/symbols/ld
index b8a8d91882..7e8aa86adc 100644
--- a/repos/base/lib/symbols/ld
+++ b/repos/base/lib/symbols/ld
@@ -208,6 +208,7 @@ _ZN6Genode4Lock4lockEv T
 _ZN6Genode4Lock6unlockEv T
 _ZN6Genode4LockC1ENS0_5StateE T
 _ZN6Genode4Slab13any_used_elemEv T
+_ZN6Genode4Slab17free_empty_blocksEv T
 _ZN6Genode4Slab5Block11_slab_entryEi T
 _ZN6Genode4Slab5Block14any_used_entryEv T
 _ZN6Genode4Slab5Block5allocEv T
diff --git a/repos/base/src/lib/base/slab.cc b/repos/base/src/lib/base/slab.cc
index 1e4bc0ba77..c8e0b7fbde 100644
--- a/repos/base/src/lib/base/slab.cc
+++ b/repos/base/src/lib/base/slab.cc
@@ -416,6 +416,17 @@ void Slab::_free(void *addr)
 }
 
 
+void Slab::free_empty_blocks()
+{
+	for (size_t blocks = _num_blocks; blocks > 0; blocks--) {
+		if (_curr_sb != _initial_sb && _curr_sb->avail() == _entries_per_block)
+			_free_curr_sb();
+		else
+			_curr_sb = _curr_sb->next;
+	}
+}
+
+
 void *Slab::any_used_elem()
 {
 	if (_total_avail == _num_blocks*_entries_per_block)