Messages in this thread | | | Date | Tue, 4 Dec 2007 15:05:58 -0500 | From | Mathieu Desnoyers <> | Subject | Re: [RFC PATCH] LTTng instrumentation mm (updated) |
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* Dave Hansen (haveblue@us.ibm.com) wrote: > On Tue, 2007-12-04 at 14:25 -0500, Mathieu Desnoyers wrote: > > > > - I also dump the equivalent of /proc/swaps (with kernel internal > > information) at trace start to know what swap files are currently > > used. > > What about just enhancing /proc/swaps so that this information can be > useful to people other than those doing traces? >
It includes an in-kernel struct file pointer, exporting it to userspace would be somewhat ugly.
> Now that we have /proc/$pid/pagemap, we expose some of the same > information about which userspace virtual addresses are stored where and > in which swapfile. >
The problems with /proc :
- It exports all the data in formatted text. What I need for my traces is pure binary, compact representation. - It's not very neat to export in-kernel pointer information like a kernel tracer would need. - The locking is very often wrong. I started correcting /proc/modules a while ago, but I fear there are quite a few cases where a procfile reader could release the locks between two consecutive reads of the same list and therefore cause missing information or corruption. While being manageable for a proc text file, this is _highly_ unwanted in a trace. See my previous "seq file sorted" and "module.c sort module list" patches about this. My tracer deals with addition/removal of elements to a list between dumps done by "chunks" by tracing the modifications done to the list at the same time. However, /proc seq files will just get corrupted or forget about an element not touched by the modification, which my tracer cannot cope with.
Mathieu
> -- Dave >
-- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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