[PATCH] latencytop: note task_struct bloat

[Hugh Dickins]

Add belated comment to LATENCYTOP help text, making clear that this is a
much more expensive option than you might think: along with the options
it selects, it may add more than 4000 bytes to each struct task_struct
(on 64-bit; more than 2000 on 32-bit), effectively quadrupling the size
of an otherwise lean task_struct (in fact, slab on x86_64 fits only 1
in two pages, whereas it fits 5 in two pages without LATENCYTOP=y).

Signed-off-by: Hugh Dickins <hugh.dickins@xxxxxxxxxxxxx>
---

 lib/Kconfig.debug |    4 ++++
 1 file changed, 4 insertions(+)

--- 2.6.30-rc8/lib/Kconfig.debug	2009-05-16 10:26:16.000000000 +0100
+++ linux/lib/Kconfig.debug	2009-06-08 18:30:50.000000000 +0100
@@ -826,6 +826,10 @@ config LATENCYTOP
 	  Enable this option if you want to use the LatencyTOP tool
 	  to find out which userspace is blocking on what kernel operations.
 
+	  Note: enabling this option may add more than 4000 bytes to each
+	  task_struct on a 64-bit kernel (more than 2000 bytes to task_struct
+	  on a 32-bit kernel), multiplying its memory usage by 4 or even 5.
+
 config SYSCTL_SYSCALL_CHECK
 	bool "Sysctl checks"
 	depends on SYSCTL_SYSCALL
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/