Comment 15 for bug 501715

Just found out about /sys/kernel/debug/tracing/buffer_size_kb
It reads 128000 on my vm which is currently showing about 322M (tracing on) 182M (tracing off) diff=140M so it looks like it is the tracing buffer.

Some questions:
1. Why is it that no application can differentiate memory used by the tracing buffer...it just looks like missing memory to everything. Is this because the tracing feature of the kernel is still new?

2. What determines the tracing buffer size? Is this a preset value?
3. Is there a way to determine how much of the tracing buffer is getting used?

Being that the minimum memory requirement for Xubuntu is 256M and 384M for Ubuntu...does it seem wise to use half of the memory for boot optimization?

Maybe a temporary fix could be to have ureadahead do nothing on systems with less than 512M of memory. Systems with this restriction would likely be old and too slow for a user to care about boot speeds anyway...especially if using ureadahead is causing the system to swap.

I am curious if ureadahead would still work if the tracing buffer size was something like 32M. 32M would be small enough for users to ignore. I don't know a lot about how tracing works, but it might be nice to have a kernel option to set the buffer size, or even control tracing.