Messages in this thread | | | Date | Thu, 1 Dec 2005 16:15:25 -0200 | From | Marcelo Tosatti <> | Subject | Re: Better pagecache statistics ? |
| |
> > I thought that it would be easy to use SystemTap for a such > > a purpose? > > > > The sys_read/sys_write example at > > http://www.redhat.com/magazine/011sep05/features/systemtap/ sounds > > interesting. > > > > What I'm I missing? > > Well, Few things: > > 1) We have to have those probes present in the system all the time > collecting the information when read/write happens, maintaining it > and spitting it out. Since its kernel probe, all this data will be > in the kernel.
Yeah, there is some overhead.
> 2) If we want to do this accounting (and you don't have those probes > installed already) - we can't capture what happened earlier.
I suppose that the vast majority of situations where such information is needed are special anyway?
Why do you need it around all the time?
> 3) probing sys_read/sys_write() are going to tell you how much > a data a process did read or wrote - but its not going to tell you > how much is in the cache (now or 10 minutes later).
Sure, that was just an example - need to insert probes on the correct places.
> > > My final goal is to get stats like .. > > > > > > Out of "Cached" value - to get details like > > > > > > <mmap> - xxx KB > > > <shared mem> - xxx KB > > > <text, data, bss, malloc, heap, stacks> - xxx KB > > > <filecache pages total> -- xxx KB > > > (filename1 or <dev>, <ino>) -- #of pages > > > (filename2 or <dev>, <ino>) -- #of pages > > > > > > This would be really powerful on understanding system better. > > > > > > Don't you think ? > > > > Yep... /proc/<pid>/smaps provides that information on a per-process > > basis already. > > /proc/pid/smaps will give me information about text,data,shared libs, > malloc etc. Not the filecache information about files process opened, > pages read/wrote currently in the pagecache. Isn't it ?
Right.
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |