I want to do some testing with an application where I need to see how long it
takes to read various scattered user data files from disk. I want to be able to
run the program whenever I want with the buffer cache empty of those user data
files.
The only way I know to do this is just reboot the system before I run the
program each time, but that is really annoying. I went searching the
documentation and found the /proc/sys/vm/buffermem file which specifies the
min_percent, borrow_percent, and max_percent of memory to use for the buffer
cache. I thought I could temporarily set the max_percent really low and then
cause a bunch of disk IO on some other files. However, the kernel documentation
disagrees about that file: the Documentation/sysctl/vm.txt file says that the
borrow_percent and map_percent fields are unused, while the
Documentation/proc.txt file makes no note of them being unused.
Another idea just to mind... what if I mount and un-mount the filesystem
containing the user files. Would that effect a buffer cache clearing for all
inodes on that filesystem?
Does anyone have a good idea how I could do this? I'd love something easy like
a /proc file that when written to expires all the clean and dirty blocks in the
buffer cache. But I'll be happy with anything easier than a system reboot.
Thanks in advance for any help.
- David Harris
Principal Engineer, DRH Internet Services
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