linux-kernel - [PATCH v2 06/24] dyndbg: fix overcounting of ram used by dyndbg

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Message-Id: <20200613155738.2249399-7-jim.cromie@gmail.com>
Date:   Sat, 13 Jun 2020 09:57:20 -0600
From:   Jim Cromie <jim.cromie@...il.com>
To:     jbaron@...mai.com, linux-kernel@...r.kernel.org,
        akpm@...uxfoundation.org, gregkh@...uxfoundation.org
Cc:     linux@...musvillemoes.dk, Jim Cromie <jim.cromie@...il.com>
Subject: [PATCH v2 06/24] dyndbg: fix overcounting of ram used by dyndbg

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
---
 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 66c0bdf06ce7..9b2445507988 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) {
 		if (IS_ENABLED(CONFIG_DYNAMIC_DEBUG)) {
@@ -1033,9 +1032,6 @@ 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);
@@ -1052,9 +1048,9 @@ 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