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    SubjectRe: [RFC] [PATCH] drop_pagecache syscall
    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 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.

    if /proc/sys/vm/drop_caches has any checks other than file permission
    checks (i.e. UID==0), it'd probably be better to copy those rather
    than picking something different.
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