From f772afc525156498900770ffe5a98349df89a45c Mon Sep 17 00:00:00 2001
From: Maria Matejka <mq@ucw.cz>
Date: Sat, 27 Nov 2021 00:21:12 +0100
Subject: Memory statistics split into Effective and Overhead

This feature is intended mostly for checking that BIRD's allocation
strategies don't consume much memory space. There are some cases where
withdrawing routes in a specific order lead to memory fragmentation and
this output should give the user at least a notion of how much memory is
actually used for data storage and how much memory is "just allocated"
or used for overhead.

Also raising the "system allocator overhead estimation" from 8 to 16
bytes; it is probably even more. I've found 16 as a local minimum in
best scenarios among reachable machines. I couldn't find any reasonable
method to estimate this value when BIRD starts up.

This commit also fixes the inaccurate computation of memory overhead for
slabs where the "system allocater overhead estimation" was improperly
added to the size of mmap-ed memory.
---
 lib/slab.c | 29 ++++++++++++++++++++++-------
 1 file changed, 22 insertions(+), 7 deletions(-)

(limited to 'lib/slab.c')

diff --git a/lib/slab.c b/lib/slab.c
index b0a01ae7..6cab6b7b 100644
--- a/lib/slab.c
+++ b/lib/slab.c
@@ -42,7 +42,7 @@
 static void slab_free(resource *r);
 static void slab_dump(resource *r);
 static resource *slab_lookup(resource *r, unsigned long addr);
-static size_t slab_memsize(resource *r);
+static struct resmem slab_memsize(resource *r);
 
 #ifdef FAKE_SLAB
 
@@ -128,7 +128,7 @@ slab_dump(resource *r)
   debug("(%d objects per %d bytes)\n", cnt, s->size);
 }
 
-static size_t
+static struct resmem
 slab_memsize(resource *r)
 {
   slab *s = (slab *) r;
@@ -138,7 +138,10 @@ slab_memsize(resource *r)
   WALK_LIST(o, s->objs)
     cnt++;
 
-  return ALLOC_OVERHEAD + sizeof(struct slab) + cnt * (ALLOC_OVERHEAD + s->size);
+  return (struct resmem) {
+    .effective = cnt * s->size,
+    .overhead = ALLOC_OVERHEAD + sizeof(struct slab) + cnt * ALLOC_OVERHEAD,
+  };
 }
 
 
@@ -363,21 +366,33 @@ slab_dump(resource *r)
   debug("(%de+%dp+%df blocks per %d objs per %d bytes)\n", ec, pc, fc, s->objs_per_slab, s->obj_size);
 }
 
-static size_t
+static struct resmem
 slab_memsize(resource *r)
 {
   slab *s = (slab *) r;
   size_t heads = 0;
   struct sl_head *h;
 
-  WALK_LIST(h, s->empty_heads)
+  WALK_LIST(h, s->full_heads)
     heads++;
+
+  size_t items = heads * s->objs_per_slab;
+
   WALK_LIST(h, s->partial_heads)
+  {
     heads++;
-  WALK_LIST(h, s->full_heads)
+    items += h->num_full;
+  }
+
+  WALK_LIST(h, s->empty_heads)
     heads++;
 
-  return ALLOC_OVERHEAD + sizeof(struct slab) + heads * (ALLOC_OVERHEAD + get_page_size());
+  size_t eff = items * s->obj_size;
+
+  return (struct resmem) {
+    .effective = eff,
+    .overhead = ALLOC_OVERHEAD + sizeof(struct slab) + heads * get_page_size() - eff,
+  };
 }
 
 static resource *
-- 
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