From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Frysinger Subject: Re: [RFC] [PATCH] drop_pagecache syscall Date: Wed, 27 Apr 2011 05:10:41 -0400 Message-ID: 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=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Dave Chinner , Andrew Morton , Al Viro , Arnd Bergmann , linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org To: Andrea Righi Return-path: In-Reply-To: <20110427085910.GA1749@linux.betterlinux.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Wed, Apr 27, 2011 at 05:01, 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: >> > This functionality can be used by all the applications that want t= o have a >> > better control over the page cache management (for example to imme= diately 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 cal= led by any >> > unprivileged application. For example, we can write a userspace to= ol to run >> > something like this: >> > >> > =A0 $ 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. if /proc/sys/vm/drop_caches has any checks other than file permission checks (i.e. UID=3D=3D0), it'd probably be better to copy those rather than picking something different.