Gday, I'm seeking some guidance on how to best (or if) to implement a feature. Please CC me on any reply, I am not subscribed to this list.
The feature is, "an application would like to know how many files another process has open". >From user space, the cheapest way would be to use the call syscall(SYS_getdents ...) in the proc/pid/fd directory. Alternatively from kernel space one could achieve a similar behavior by iterating through the tasks fdtable, as i have attempted to here: https://gist.github.com/wmealing/c0836bc6a38f8f90aa0d Colleagues of mine have pointed out that this may have performance impacts for tools that frequently parse /proc/pid/status. I have compiled a kernel with the above patch and here are the performance stats. System settings # sysctl -w fs.file-max=5000000 fs.file-max = 5000000 Increase this sessions limits. # ulimit -n 1000000 test.py had 500002 files open each time. Here are some of the performance benchmarks on an idle system: # time cat /proc/`pidof python test.py`/status |grep FD FDSize: 524288 FDCount: 500002 real 0m0.008s user 0m0.002s sys 0m0.004s # time ./test-getdents /proc/`pidof python test.py`/fd &> /dev/null real 0m0.631s user 0m0.001s sys 0m0.485s or this time with readdir(3) # time ./test-opendir /proc/`pidof python test.py`/fd &> /dev/null real 0m0.129s user 0m0.001s sys 0m0.007s (which oddly seems faster?) My benchmark values above are not meant for micro-benchmarking but rather as a scale to know how far behind the code is. Is the current method of getting a live fd count acceptable, if not how should it be done ? Thanks for your time. Wade Mealing. [1] https://github.com/wmealing/live-fd-count/ git repo with code used in the above. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
