From: Frank Ch. Eigler <fche@elastic.org>
Date: Wed, 12 Aug 2009 20:07:08 +0000 (-0400)
Subject: PR10507: tweak heuristics for stap_uprobes[] allocation
X-Git-Tag: release-1.0~167
X-Git-Url: https://sourceware.org/git/?a=commitdiff_plain;h=43241c442263dd52e34f86e2d0a64c20cd7235c3;p=systemtap.git

PR10507: tweak heuristics for stap_uprobes[] allocation

* tapsets.cxx (uprobes::emit_module_decls): Compute MAXUPROBES
  with x-treme kl3v3rn3ss.
* stap.1.in: Clarify MAXUPROBES.
---

diff --git a/stap.1.in b/stap.1.in
index 0e7a51f48..a9af3a132 100644
--- a/stap.1.in
+++ b/stap.1.in
@@ -1081,9 +1081,9 @@ for the probe handler's own needs, plus a safety margin.
 .TP
 MAXUPROBES
 Maximum number of concurrently armed user-space probes (uprobes), default
-100 times the number of user-space probe points named in the script.  This
-pool is large because individual uprobe objects are allocated for each
-process for each script-level probe.
+somewhat larger than the number of user-space probe points named in the script.
+This pool needs to be potentialy large because individual uprobe objects (about
+64 bytes each) are allocated for each process for each matching script-level probe.
 
 .PP
 With scripts that contain probes on any interrupt path, it is possible that
diff --git a/tapsets.cxx b/tapsets.cxx
index 9884860a5..333914d0e 100644
--- a/tapsets.cxx
+++ b/tapsets.cxx
@@ -4400,12 +4400,19 @@ uprobe_derived_probe_group::emit_module_decls (systemtap_session& s)
   s.op->newline() << "#define UPROBES_API_VERSION 1";
   s.op->newline() << "#endif";
 
-  s.op->newline() << "#ifndef MULTIPLE_UPROBES";
-  s.op->newline() << "#define MULTIPLE_UPROBES 256"; // maximum possible armed uprobes per process() probe point
-						     // or apprx. max number of processes mapping a shared library
-  s.op->newline() << "#endif";
+  // We'll probably need at least this many:
+  unsigned minuprobes = probes.size();
+  // .. but we don't want so many that .bss is inflated (PR10507):
+  unsigned uprobesize = 64;
+  unsigned maxuprobesmem = 10*1024*1024; // 10 MB
+  unsigned maxuprobes = maxuprobesmem / uprobesize;
+
+  // Let's choose a value on the middle, but clamped on the minimum size
+  unsigned default_maxuprobes = 
+    (minuprobes < maxuprobes) ? ((minuprobes + maxuprobes) / 2) : minuprobes;
+
   s.op->newline() << "#ifndef MAXUPROBES";
-  s.op->newline() << "#define MAXUPROBES (MULTIPLE_UPROBES * " << probes.size() << ")";
+  s.op->newline() << "#define MAXUPROBES " << default_maxuprobes;
   s.op->newline() << "#endif";
 
   // In .bss, the shared pool of uprobe/uretprobe structs.  These are