From a65d634e63644d05a22f32e5f2e56dde4f7ee77b Mon Sep 17 00:00:00 2001 From: "Frank A. Cancio Bello" Date: Tue, 24 Dec 2019 19:06:05 -0500 Subject: docs: ftrace: Clarify the RAM impact of buffer_size_kb The current text could mislead the user into believing that the number of pages allocated by each CPU ring buffer is calculated by the round up of the division: buffer_size_kb / PAGE_SIZE. Clarifies that a few extra pages may be allocated to accommodate buffer management meta-data. Suggested-by: Steven Rostedt (VMware) Suggested-by: Joel Fernandes (Google) Reviewed-by: Steven Rostedt (VMware) Reviewed-by: Joel Fernandes (Google) Signed-off-by: Frank A. Cancio Bello Link: https://lore.kernel.org/r/6f33be5f3d60e5ffc061d8d2b329d3d3ccf22a8c.1577231751.git.frank@generalsoftwareinc.com Signed-off-by: Jonathan Corbet --- Documentation/trace/ftrace.rst | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'Documentation/trace') diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst index 46df39300d22..8575aed7b74b 100644 --- a/Documentation/trace/ftrace.rst +++ b/Documentation/trace/ftrace.rst @@ -187,7 +187,8 @@ of ftrace. Here is a list of some of the key files: CPU buffer and not total size of all buffers. The trace buffers are allocated in pages (blocks of memory that the kernel uses for allocation, usually 4 KB in size). - If the last page allocated has room for more bytes + A few extra pages may be allocated to accommodate buffer management + meta-data. If the last page allocated has room for more bytes than requested, the rest of the page will be used, making the actual allocation bigger than requested or shown. ( Note, the size may not be a multiple of the page size -- cgit v1.2.3