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Date: Mon, 29 Jul 2013 10:14:23 +0800 From: Li Zefan <lizefan@...wei.com> To: Steven Rostedt <rostedt@...dmis.org> CC: Borislav Petkov <bp@...en8.de>, Frederic Weisbecker <fweisbec@...il.com>, LKML <linux-kernel@...r.kernel.org> Subject: [PATCH v3 2/2] tracing: Shrink the size of struct ftrace_event_field Use bit fields, and the size of struct ftrace_event_field can be shrunk from 48 bytes to 40 bytes on 64bit kernel. slab_name active_obj nr_obj size obj_per_slab --------------------------------------------- ftrace_event_field 1105 1105 48 85 (before) ftrace_event_field 1224 1224 40 102 (after) This saves a few Kbytes: (1224 * 40) - (1105 * 48) = 4080 v2: - use !!is_signed, and nuke the check on this field. - use a different way to detect overflow. (both suggested by Steven) v3: - use plain WARN_ON() instead of a macro. (suggeusted by Borislav) Signed-off-by: Li Zefan <lizefan@...wei.com> --- kernel/trace/trace.h | 8 ++++---- kernel/trace/trace_events.c | 12 ++++++++---- 2 files changed, 12 insertions(+), 8 deletions(-) diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index 4a4f6e1..3e8c97f 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -904,10 +904,10 @@ struct ftrace_event_field { struct list_head link; const char *name; const char *type; - int filter_type; - int offset; - int size; - int is_signed; + unsigned int filter_type:4; + unsigned int offset:12; + unsigned int size:12; + unsigned int is_signed:1; }; struct event_filter { diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c index 7d85429..6509afe 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -120,13 +120,17 @@ static int __trace_define_field(struct list_head *head, const char *type, field->type = type; if (filter_type == FILTER_OTHER) - field->filter_type = filter_assign_type(type); - else - field->filter_type = filter_type; + filter_type = filter_assign_type(type); + field->filter_type = filter_type; field->offset = offset; field->size = size; - field->is_signed = is_signed; + field->is_signed = !!is_signed; + + /* detect bit-field overflow */ + WARN_ON(filter_type > field->filter_type); + WARN_ON(offset > field->offset); + WARN_ON(size > field->size); list_add(&field->link, head); -- 1.8.0.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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