From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joel Becker Subject: Re: [RFC] [PATCH] drop_pagecache syscall Date: Thu, 28 Apr 2011 16:22:10 -0700 Message-ID: <20110428232210.GA4132@noexit.corp.google.com> References: <1303853727-21444-1-git-send-email-andrea@betterlinux.com> <20110427001453.GD12436@dastard> <20110427085910.GA1749@linux.betterlinux.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Dave Chinner , Andrew Morton , Al Viro , Arnd Bergmann , linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Andrea Righi Return-path: Content-Disposition: inline In-Reply-To: <20110427085910.GA1749-Td79XgCuBx/ToqTmb/eOq0M9+F4ksjoh@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-fsdevel.vger.kernel.org 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. > > > 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/ jlbec-aKy9MeLSZ9dg9hUCZPvPmw@public.gmane.org