On Friday 29 April 2011, Andrea Righi wrote: > NOTE #1: to avoid potential DoS in the system the rate of calls to > fadvise(POSIX_FADV_DONTNEED_FS) from non-privileged users are limited > according to these settings: > > - /proc/sys/vm/drop_pagecache_ratelimit: the minimum length of time > allowed beetween two different bursts of fadvise(POSIX_FADV_DONTNEED_FS) > > - /proc/sys/vm/drop_pagecache_ratelimit_burst: the number of calls to > fadvise(POSIX_FADV_DONTNEED_FS) that can be issued before enforcing > the rate limiting The ratelimiting interface does not give me the happy feeling I had with the original extremely syscall and fadvise, or with strictly limiting it to certain capabilities. The ratelimit bursts seem well suited for log messages, but it's not like you would expect anyone to read the fadvise man page describing these and think "oh, of course, that's obviously why it has to be done this way". I don't have a perfect solution myself, but there are a few things that feel wrong about yours: * The rules for /proc/sys/vm/drop_caches and the fadvise are different * You need to tune two variables to set one thing * The rate limit is independent of the number of file systems you operate on: When you have mounted 20 file systems, you need to sleep for five seconds after flushing half of them, but you can flush one ten times in a row without being throttled. * Returning an error gives no feedback about how soon it can be retried, in case you really need to flush. Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
