[PATCH 05/16] dyndbg: fix overcounting of ram used by dyndbg

[PATCH 05/16] dyndbg: fix overcounting of ram used by dyndbg

[Jim Cromie]

during dyndbg init, verbose logging prints its ram overhead.  It
counted strlens of struct _ddebug's 4 string members, in all callsite
entries, which would be approximately correct if each had been
mallocd.  But they are pointers into shared .rodata; for example, all
10 kobject callsites have identical filename, module values.

Its best not to count that memory at all, since we cannot know they
were linked in because of CONFIG_DYNAMIC_DEBUG=y, and we want to
report a number that reflects what ram is saved by deconfiguring it.

Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
 lib/dynamic_debug.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index 0a4588fe342e..b5fb0aa0fbc3 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -1008,7 +1008,6 @@ static int __init dynamic_debug_init(void)
 	char *cmdline;
 	int ret = 0;
 	int n = 0, entries = 0, modct = 0;
-	int verbose_bytes = 0;
 
 	if (__start___dyndbg == __stop___dyndbg) {
 		pr_warn("_ddebug table is empty in a CONFIG_DYNAMIC_DEBUG build\n");
@@ -1019,9 +1018,6 @@ static int __init dynamic_debug_init(void)
 	iter_start = iter;
 	for (; iter < __stop___dyndbg; iter++) {
 		entries++;
-		verbose_bytes += strlen(iter->modname) + strlen(iter->function)
-			+ strlen(iter->filename) + strlen(iter->format);
-
 		if (strcmp(modname, iter->modname)) {
 			modct++;
 			ret = ddebug_add_module(iter_start, n, modname);
@@ -1038,9 +1034,9 @@ static int __init dynamic_debug_init(void)
 		goto out_err;
 
 	ddebug_init_success = 1;
-	vpr_info("%d modules, %d entries and %d bytes in ddebug tables, %d bytes in (readonly) verbose section\n",
+	vpr_info("%d modules, %d entries and %d bytes in ddebug tables, %d bytes in __dyndbg section\n",
 		 modct, entries, (int)(modct * sizeof(struct ddebug_table)),
-		 verbose_bytes + (int)(__stop___dyndbg - __start___dyndbg));
+		 (int)(entries * sizeof(struct _ddebug)));
 
 	/* apply ddebug_query boot param, dont unload tables on err */
 	if (ddebug_setup_string[0] != '\0') {
-- 
2.23.0

Re: [PATCH 05/16] dyndbg: fix overcounting of ram used by dyndbg

[Rasmus Villemoes]

On 27/11/2019 18.50, Jim Cromie wrote:
> during dyndbg init, verbose logging prints its ram overhead.  It
> counted strlens of struct _ddebug's 4 string members, in all callsite
> entries, which would be approximately correct if each had been
> mallocd.  But they are pointers into shared .rodata; for example, all
> 10 kobject callsites have identical filename, module values.
> 
> Its best not to count that memory at all, since we cannot know they
> were linked in because of CONFIG_DYNAMIC_DEBUG=y, and we want to
> report a number that reflects what ram is saved by deconfiguring it.

That, and we avoid 1000s of (mostly cache-cold) strlen() calls during boot.

Acked-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>

I'll see if I can find time to review the other patches, then I think
you need to resend with Andrew on the cc-list (added here). I think he's
the one routing lib/dynamic_debug.c patches.

Rasmus

[PATCH 00/16] dynamic_debug: cleanups, 2 features

[Jim Cromie]

Patchset starts with 7 "cleanups";
- it changes section name from vague "__verbose" to "__dyndbg"
- cleaner docs, drop obsolete comment & useless debug prints, refine
  verbosity, fix a BUG_ON, ram reporting miscounts.

It adds a few query parsing conveniences;
accept combined file:line & file:func forms

  file inode.c:100-200		# file & line-range
  file inode.c:start_*		# file & function

Then it expands flags:

Adds 'u' user flag, allowing user to compose an arbitrary set of
callsites by marking them with 'u', without altering current
print-modifying flags.

Adds 'PFMLTU' flags, which negate their lower-case counterparts.

Extends flags-spec with filter-flags, which select callsites for
modification based upon their current flags.  This lets user activate
the set of callsites marked with 'u' in a batch.

  echo 'u+p' > control

This was previously submitted before events overtook.
 v1: https://lkml.org/lkml/2019/10/29/989
 v2: https://lkml.org/lkml/2019/11/27/547

Jim Cromie (16):
cleanups:
  dyndbg-docs: eschew file /full/path query in docs
  dyndbg: drop obsolete comment on ddebug_proc_open
  dyndbg: refine debug verbosity
  dyndbg: rename __verbose section to __dyndbg
  dyndbg: fix overcounting of ram used by dyndbg
  dyndbg: fix a BUG_ON in ddebug_describe_flags
  dyndbg: make ddebug_tables list LIFO for add/remove_module
new features:
-parsing conveniences
  dyndbg: refactor parse_linerange out of ddebug_parse_query
  dyndbg: accept 'file foo.c:func1' and 'file foo.c:10-100'
-flags extensions
--internal rework
  dyndbg: refactor ddebug_read_flags out of ddebug_parse_flags
  dyndbg: combine flags & mask into a struct, use that
  dyndbg: add filter parameter to ddebug_parse_flags
  dyndbg: extend ddebug_parse_flags to accept optional filter-flags
  dyndbg: prefer declarative init in caller, to memset in callee
--expose the features
  dyndbg: add user-flag, negating-flags, and filtering on flags
  dyndbg: allow negating flag-chars in modflags

 .../admin-guide/dynamic-debug-howto.rst       |  75 +++--
 include/asm-generic/vmlinux.lds.h             |   6 +-
 include/linux/dynamic_debug.h                 |   5 +-
 kernel/module.c                               |   2 +-
 lib/dynamic_debug.c                           | 282 ++++++++++--------
 5 files changed, 225 insertions(+), 145 deletions(-)

-- 
2.26.2

[PATCH 05/16] dyndbg: fix overcounting of ram used by dyndbg

[Jim Cromie]

during dyndbg init, verbose logging prints its ram overhead.  It
counted strlens of struct _ddebug's 4 string members, in all callsite
entries, which would be approximately correct if each had been
mallocd.  But they are pointers into shared .rodata; for example, all
10 kobject callsites have identical filename, module values.

Its best not to count that memory at all, since we cannot know they
were linked in because of CONFIG_DYNAMIC_DEBUG=y, and we want to
report a number that reflects what ram is saved by deconfiguring it.

Also fix wording and size under-reporting of the __dyndbg section.

Heres my overhead, on a virtme-run VM on a fedora-31 laptop:

  dynamic_debug:dynamic_debug_init: 260 modules, 2479 entries \
    and 10400 bytes in ddebug tables, 138824 bytes in __dyndbg section

Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
 lib/dynamic_debug.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index e17d4e2661d8..25cc1eb86d96 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -1017,7 +1017,6 @@ static int __init dynamic_debug_init(void)
 	char *cmdline;
 	int ret = 0;
 	int n = 0, entries = 0, modct = 0;
-	int verbose_bytes = 0;
 
 	if (&__start___dyndbg == &__stop___dyndbg) {
 		pr_warn("_ddebug table is empty in a CONFIG_DYNAMIC_DEBUG build\n");
@@ -1028,9 +1027,6 @@ static int __init dynamic_debug_init(void)
 	iter_start = iter;
 	for (; iter < __stop___dyndbg; iter++) {
 		entries++;
-		verbose_bytes += strlen(iter->modname) + strlen(iter->function)
-			+ strlen(iter->filename) + strlen(iter->format);
-
 		if (strcmp(modname, iter->modname)) {
 			modct++;
 			ret = ddebug_add_module(iter_start, n, modname);
@@ -1047,9 +1043,9 @@ static int __init dynamic_debug_init(void)
 		goto out_err;
 
 	ddebug_init_success = 1;
-	vpr_info("%d modules, %d entries and %d bytes in ddebug tables, %d bytes in (readonly) verbose section\n",
+	vpr_info("%d modules, %d entries and %d bytes in ddebug tables, %d bytes in __dyndbg section\n",
 		 modct, entries, (int)(modct * sizeof(struct ddebug_table)),
-		 verbose_bytes + (int)(__stop___dyndbg - __start___dyndbg));
+		 (int)(entries * sizeof(struct _ddebug)));
 
 	/* apply ddebug_query boot param, dont unload tables on err */
 	if (ddebug_setup_string[0] != '\0') {
-- 
2.26.2