lkml.org 
[lkml]   [2007]   [Jan]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH 0/8] Create ZONE_MOVABLE to partition memory between movable and non-movable pages
    On Fri, 26 Jan 2007, Andrew Morton wrote:

    > On Thu, 25 Jan 2007 23:44:58 +0000 (GMT)
    > Mel Gorman <mel@csn.ul.ie> wrote:
    >
    >> The following 8 patches against 2.6.20-rc4-mm1 create a zone called
    >> ZONE_MOVABLE
    >
    > Argh. These surely get all tangled up with the
    > make-zones-optional-by-adding-zillions-of-ifdef patches:
    >

    There may be some entertainment there all right. I didn't see any obvious
    way of avoiding collisions with those patches but for what it's worth,
    ZONE_MOVABLE could also be made optional.

    In this patchset, I made no assumptions about the number of zones other
    than the value of MAX_NR_ZONES. There should be no critical collisions but
    I'll look through this patch list and see what I can spot.

    > deal-with-cases-of-zone_dma-meaning-the-first-zone.patch

    This patch looks ok and looks like it stands on it's own.

    > introduce-config_zone_dma.patch

    ok, no collisions here but obviously this patch does not stand on it's
    own.

    > optional-zone_dma-in-the-vm.patch

    There are collisions here with the __ZONE_COUNT stuff but it's not
    difficult to work around.

    > optional-zone_dma-in-the-vm-no-gfp_dma-check-in-the-slab-if-no-config_zone_dma-is-set.patch
    > optional-zone_dma-in-the-vm-no-gfp_dma-check-in-the-slab-if-no-config_zone_dma-is-set-reduce-config_zone_dma-ifdefs.patch

    There is no cross-over here with the ZONE_MOVABLE patches. They are
    messing around with slab

    > optional-zone_dma-for-ia64.patch

    No collision here

    > remove-zone_dma-remains-from-parisc.patch
    > remove-zone_dma-remains-from-sh-sh64.patch

    No collisions here either. I see that there were discussions about Power
    potentially doing something similar.

    > set-config_zone_dma-for-arches-with-generic_isa_dma.patch

    No collisions

    > zoneid-fix-up-calculations-for-zoneid_pgshift.patch
    >

    Fun, but no collisions.

    To my suprise, I only spotted one major conflict point with
    optional-zone_dma-in-the-vm.patch and that should be easy enough to
    resolve. What I could do is break up one of my patches into
    most-of-the-patch and the-part-that-may-conflict-with-optional-dma-zone .
    The smaller part would then change depending on whether the optional DMA
    zone work is present. Would that be any help?

    > My objections to those patches:
    >
    > - They add zillions of ifdefs
    >
    > - They make the VM's behaviour diverge between different platforms and
    > between differen configs on the same platforms, and hence degrade
    > maintainability and increase complexity.
    >

    I haven't thought about it much so I probably am missing something. The
    major difference I see is when only one zone is present. In that case, a
    number of loops presumably get optimised away and the behavior is very
    different (presumably better although you point out no figures exist to
    prove it). Where there are two or more zones, the code paths should be
    similar whether there are 2, 3 or 4 zones present.

    As the common platforms will always have more than one zone, it'll be
    heavily tested and I'm guessing that distros are always going to have to
    ship kernels with ZONE_DMA for the devices that require it. The only
    platform I see that may have problems at the moment is IA64 which looks
    like the only platform that can have one and only one zone. I am guessing
    that Christoph will catch problems here fairly quickly although a
    non-optional ZONE_MOVABLE would throw a spanner into the works somewhat.

    > - We kicked around some quite different ways of implementing the same
    > things, but nothing came of it. iirc, one was to remove the hard-coded
    > zones altogether and rework all the MM to operate in terms of
    >
    > for (idx = 0; idx < NUMBER_OF_ZONES; idx++)
    > ...
    >

    hmm. Assuming the aim is to have a situation where all zone-related loops
    are optimised away at compile-time, it's hard to see an alternative that
    works. Any dynamic way of creating zone at boot time will not have the
    compile-time optimizations and any API that is page-range aware will
    eventually hit the problems zones were made to solve (i.e. unmovable pages
    locked in the lower address ranges).

    > - I haven't seen any hard numbers to justify the change.
    >
    > So I want to drop them all.
    >

    --
    Mel Gorman
    Part-time Phd Student Linux Technology Center
    University of Limerick IBM Dublin Software Lab
    -
    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: 2007-01-26 15:33    [W:3.866 / U:0.104 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site