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    SubjectRe: [PATCH 0/8] v5 De-couple sysfs memory directories from memory sections
    On Mon, 09 Aug 2010 12:53:00 -0500
    Nathan Fontenot <> wrote:

    > This set of patches de-couples the idea that there is a single
    > directory in sysfs for each memory section. The intent of the
    > patches is to reduce the number of sysfs directories created to
    > resolve a boot-time performance issue. On very large systems
    > boot time are getting very long (as seen on powerpc hardware)
    > due to the enormous number of sysfs directories being created.
    > On a system with 1 TB of memory we create ~63,000 directories.
    > For even larger systems boot times are being measured in hours.

    And those "hours" are mainly due to this problem, I assume.

    > This set of patches allows for each directory created in sysfs
    > to cover more than one memory section. The default behavior for
    > sysfs directory creation is the same, in that each directory
    > represents a single memory section. A new file 'end_phys_index'
    > in each directory contains the physical_id of the last memory
    > section covered by the directory so that users can easily
    > determine the memory section range of a directory.

    What you're proposing appears to be a non-back-compatible
    userspace-visible change. This is a big issue!

    It's not an unresolvable issue, as this is a must-fix problem. But you
    should tell us what your proposal is to prevent breakage of existing
    installations. A Kconfig option would be good, but a boot-time kernel
    command line option which selects the new format would be much better.

    However you didn't mention this issue at all, and it's the most
    important one.

    > Updates for version 5 of the patchset include the following:
    > Patch 4/8 Add mutex for add/remove of memory blocks
    > - Define the mutex using DEFINE_MUTEX macro.
    > Patch 8/8 Update memory-hotplug documentation
    > - Add information concerning memory holes in phys_index..end_phys_index.

    And you forgot to tell us how long those machines boot with the
    patchset applied, which is the entire point of the patchset!

     \ /
      Last update: 2010-08-12 21:11    [W:0.021 / U:3.652 seconds]
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