lkml.org 
[lkml]   [2003]   [Apr]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: objrmap and vmtruncate
    On Sat, Apr 05, 2003 at 01:24:06PM -0800, Andrew Morton wrote:
    > Andrea Arcangeli <andrea@suse.de> wrote:
    > >
    > > On Sat, Apr 05, 2003 at 04:06:14AM -0800, Andrew Morton wrote:
    > > > Andrew Morton <akpm@digeo.com> wrote:
    > > > >
    > > > > Nobody has written an "exploit" for this yet, but it's there.
    > > >
    > > > Here we go. The test app is called `rmap-test'. It is in ext3 CVS. See
    > > >
    > > > http://www.zip.com.au/~akpm/linux/ext3/
    > > >
    > > > It sets up N MAP_SHARED VMA's and N tasks touching them in various access
    > > > patterns.
    > >
    > > I'm not questioning during paging rmap is more efficient than objrmap,
    > > but your argument about rmap having lower complexity of objrmap and that
    > > rmap is needed is wrong. The fact is that with your 100 mappings per
    > > each of the 100 tasks case, both algorithms works in O(N) where N is
    > > the number of the pagetables mapping the page.
    >
    > Nope. To unmap a page, full rmap has to scan 100 pte_chain slots, which is 3
    > cachelines worth. objrmap has to scan 10,000 vma's, 9,900 of which do not map
    > that page at all.

    I see what you mean, you're right. That's because all the 10,000 vma
    belongs to the same inode.

    Andrea
    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2005-03-22 13:34    [W:0.023 / U:118.700 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site