Hello,

I was curious if there were any hooks into the part of the kernel that handles the buffer cache (or hard disk bytes transferred) for finding the amount of data that has moved through the cache per second.

(ie like top)

 

Or if there was a way from a program to tell how much data has moved from disk (read / written) per second in order to trigger a directory listing when say 3GB has been read or written to disk on a 4GB system so that the unRaid Server might have a chance to sleep when the disk contents aren't being read or written?

but, when disk activity resumes it has a chance to refresh the directory listings ... before the 3GB limit is again reached

 

ie .. for every 3GB read or written on a 4GB system (75% of memory) it will do a complete directory listing keeping the dentry entries fresh ... but if there is no disk activity the system will have a chance to sleep rather than doing directory listings every minute. (or 30s, or 10s)

 

Thanks for your time,

Bobby

 

ps -- sorry for the lack of sleep as you can see in my post

 

dentry listing in PROC arent as reliable and consistent as you may think. Even on a system where nothing is obviously  happening the dentry figures change slightly.

 

Heres an example of 10 second dumps on my system with all disks spun down:

 

9092 282751

9093 282755

9094 282758

9095 282763

9096 282761

9097 282764

9098 282768

9099 282767

 

the first number is just a timer and not relevant.

 

Something like what you suggested occurred to me previously but I dont think it is viable as there are so many mechanisms in play here it would be hard to make it work. The documentaion on it also sucks and I suspect people are supposed to look at the code to really understand how it works.

 

What we really need is someone to talk to a kernel developer and explain the situation and ask them to look at what is in my opinion either a kernel bug or at the very least a misleading set of documentation for cache pressure. I have tried via IRC but it goes over the head of the people that actually hang about in that channel.