ureadahead patch

[Chase Douglas]

On Thu, 2010-07-08 at 10:24 -0600, Tim Gardner wrote:
> diff -u ureadahead-0.100.0/debian/changelog ureadahead-0.100.0/debian/changelog
> --- ureadahead-0.100.0/debian/changelog
> +++ ureadahead-0.100.0/debian/changelog
> @@ -1,3 +1,9 @@
> +ureadahead (0.100.0-5ubuntu1) maverick; urgency=low
> +
> +  * 
> +
> + -- Tim Gardner <rtg at lochsa>  Thu, 08 Jul 2010 16:04:39 +0000
> +
>  ureadahead (0.100.0-5) maverick; urgency=low
>  
>    * src/pack.c: Amend mount point detection logic to stat the mount point
> only in patch2:
> unchanged:
> --- ureadahead-0.100.0.orig/src/trace.c
> +++ ureadahead-0.100.0/src/trace.c
> @@ -122,6 +122,7 @@
>  	int                 old_open_exec_enabled = 0;
>  	int                 old_uselib_enabled = 0;
>  	int                 old_tracing_enabled = 0;
> +	int                 old_buffer_size_kb = 0;
>  	struct sigaction    act;
>  	struct sigaction    old_sigterm;
>  	struct sigaction    old_sigint;
> @@ -165,7 +166,7 @@
>  
>  		old_uselib_enabled = -1;
>  	}
> -	if (set_value (dfd, "buffer_size_kb", 128000, NULL) < 0)
> +	if (set_value (dfd, "buffer_size_kb", 128000, &old_buffer_size_kb) < 0)
>  		goto error;
>  	if (set_value (dfd, "tracing_enabled",
>  		       TRUE, &old_tracing_enabled) < 0)
> @@ -217,6 +218,9 @@
>  	if (set_value (dfd, "events/fs/do_sys_open/enable",
>  		       old_sys_open_enabled, NULL) < 0)
>  		goto error;
> +	if (set_value (dfd, "buffer_size_kb",
> +		       old_buffer_size_kb, NULL) < 0)
> +		goto error;
>  
>  	/* Be nicer */
>  	if (nice (15))
> 

I'm guessing that set_value copies what would be the result of "cat
buffer_size_kb" into old_buffer_size_kb. Unfortunately, that would end
up with:

7 (expanded: 1408)

Or something like that. This output signifies that at first we only have
7 KB/cpu of buffer, but as soon as a function trace is started we
allocate 1408 KB/cpu. When you manually change the value, you
automatically get pushed to the expanded state. This is a one-way
operation; we can't go back to the original state once we bump the value
in ureadahead.

I think that the best thing is to just set it back to 1 (a minimum
value). If someone wants to do a trace, they can bump this value up. I'm
wary of even going back to the expanded value because in the vast
majority of cases we're just wasting memory.

-- Chase