lkml.org 
[lkml]   [2009]   [Nov]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: Subject: [RFC MM] mmap_sem scaling: Use mutex and percpu counter instead
    On Thu, Nov 05, 2009 at 04:03:39PM -0500, Christoph Lameter wrote:
    > > For example it will definitely impact the AIM7 multi brk() issue
    > > or the mysql allocation case, which are all writer intensive. I assume
    > > doing a lot of mmaps/brks in parallel is not that uncommon.
    >
    > No its not that common. Page faults are much more common. The AIM7 seems
    > to be an artificial case? What does mysql do for allocation? If its brk()

    AIM7 is artificial yes, but I suspect similar problems (to a less
    extreme degree) are in other workloads.

    > related then simply going to larger increases may fix the issue??

    For mysql it's mmap through malloc(). There has been some tuning in
    glibc for it. But I suspect it's a more general problem that will
    still need kernel improvements.

    >
    > > My thinking was more that we simply need per VMA locking or
    > > some other per larger address range locking. Unfortunately that
    > > needs changes in a lot of users that mess with the VMA lists
    > > (perhaps really needs some better abstractions for VMA list management
    > > first)
    >
    > We have range locking through the distribution of the ptl for systems with
    > more than 4 processors. One can use that today to lock ranges of the
    > address space.

    Yes but all the major calls still take mmap_sem, which is not ranged.

    -Andi
    --
    ak@linux.intel.com -- Speaking for myself only.


    \
     
     \ /
      Last update: 2009-11-06 08:43    [W:3.875 / U:0.008 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site