On Thu, Apr 28, 2011 at 04:22:10PM -0700, Joel Becker wrote: > On Wed, Apr 27, 2011 at 11:01:28AM +0200, Andrea Righi wrote: > > On Wed, Apr 27, 2011 at 10:14:53AM +1000, Dave Chinner wrote: > > > On Tue, Apr 26, 2011 at 11:35:27PM +0200, Andrea Righi wrote: > > > > Introduce sys_drop_pagecache() system call to drop the page cache pages of > > > > a single filesystem. > <snip> > > > > This functionality can be used by all the applications that want to have a > > > > better control over the page cache management (for example to immediately drop > > > > pages that for sure will not be reused in the near future, without calling > > > > posix_fadvise() for all the files they've touched), or to provide a more fine > > > > grained debugging feature usable by the filesystem benchmarks. > > > > > > > > The system call does not require root privileges and it can be called by any > > > > unprivileged application. For example, we can write a userspace tool to run > > > > something like this: > > > > > > > > $ drop-pagecache /path/file_or_dir > > > > > > That's a potential DOS vector, I think. Drop the pagecache in a hard > > > loop on the root fs of a busy server and watch it crawl... > > > > Yes, probably we could allow only the CAP_SYS_ADMIN tasks to execute > > this syscall. > > The majority of apps that want this do not run as root. Do we > want them all setuid? ;-) Another solution could be to limit the rate of this syscall if executed by a non-privileged user. And the rate limit could be also configurable from userspace via /proc/sys/vm/ or something similar. -Andrea -- 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
