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tracing: Limit trace_seq size to just 8K and not depend on architecture PAGE_SIZE

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The trace_seq buffer is used to print out entire events. It's typically
set to PAGE_SIZE * 2 as there's some events that can be quite large.

As a side effect, writes to trace_marker is limited by both the size of the
trace_seq buffer as well as the ring buffer's sub-buffer size (which is a
power of PAGE_SIZE). By limiting the trace_seq size, it also limits the
size of the largest string written to trace_marker.

trace_seq does not need to be dependent on PAGE_SIZE like the ring buffer
sub-buffers need to be. Hard code it to 8K which is PAGE_SIZE * 2 on most
architectures. This will also limit the size of trace_marker on those
architectures with greater than 4K PAGE_SIZE.

Link: https://lore.kernel.org/all/20240302111244.3a1674be@gandalf.local.home/
Link: https://lore.kernel.org/linux-trace-kernel/20240304191342.56fb1087@gandalf.local.home

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Sachin Sant <sachinp@linux.ibm.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt (Google) 2024-03-04 19:13:42 -05:00
parent 5efd3e2aef
commit 6f42249fec
1 changed files with 7 additions and 1 deletions
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8
include/linux/trace_seq.h
View File

@ -9,9 +9,15 @@
/*
* Trace sequences are used to allow a function to call several other functions
* to create a string of data to use.
*
* Have the trace seq to be 8K which is typically PAGE_SIZE * 2 on
* most architectures. The TRACE_SEQ_BUFFER_SIZE (which is
* TRACE_SEQ_SIZE minus the other fields of trace_seq), is the
* max size the output of a trace event may be.
*/
#define TRACE_SEQ_BUFFER_SIZE (PAGE_SIZE * 2 - \
#define TRACE_SEQ_SIZE 8192
#define TRACE_SEQ_BUFFER_SIZE (TRACE_SEQ_SIZE - \
(sizeof(struct seq_buf) + sizeof(size_t) + sizeof(int)))
struct trace_seq {