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? ;-)
Joel
--
"If the human brain were so simple we could understand it, we would
be so simple that we could not."
- W. A. Clouston
http://www.jlbec.org/
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