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authorFrank A. Cancio Bello <frank@generalsoftwareinc.com>2019-12-25 03:06:05 +0300
committerJonathan Corbet <corbet@lwn.net>2020-01-10 20:51:34 +0300
commita65d634e63644d05a22f32e5f2e56dde4f7ee77b (patch)
treec5fa0a12b5e2845a74dab7d3727d4624a6116d41 /Documentation/trace
parent6f7f8ef713a24ccea341a7f0cb92ef2b6b297f01 (diff)
downloadlinux-a65d634e63644d05a22f32e5f2e56dde4f7ee77b.tar.xz
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) <rostedt@goodmis.org> Suggested-by: Joel Fernandes (Google) <joel@joelfernandes.org> Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org> Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org> Signed-off-by: Frank A. Cancio Bello <frank@generalsoftwareinc.com> Link: https://lore.kernel.org/r/6f33be5f3d60e5ffc061d8d2b329d3d3ccf22a8c.1577231751.git.frank@generalsoftwareinc.com Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Diffstat (limited to 'Documentation/trace')
-rw-r--r--Documentation/trace/ftrace.rst3
1 files changed, 2 insertions, 1 deletions
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