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    SubjectRe: [uml-devel] [PATCH 5/6] slab: Annotate slab
    Hi Steve,

    On Wed, Sep 3, 2008 at 8:08 AM, Steve VanDeBogart
    <vandebo-lkml@nerdbox.net> wrote:
    > Thank you for pointing out the location of the kmemcheck code. I looked
    > around briefly but didn't find the latest version. It does seem that
    > kmemcheck and Valgrind annotations want to live in the same places so it
    > makes perfect sense to combine them where possible. I'm not exactly sure
    > what you find so ugly about the Valgrind annotations, please elaborate.

    Upper case macros and littering #ifdefs in the code. See the kmemcheck
    hooks how to do it in a clean way.

    On Wed, Sep 3, 2008 at 8:08 AM, Steve VanDeBogart
    <vandebo-lkml@nerdbox.net> wrote:
    > It is true that code above the allocator should not be touching free'd
    > slab objects. However, it is also true that objects from slabs that
    > have a constructor should retain their per byte un/initialized state
    > through allocation and free cycles (just the semantic of slabs with
    > constructors AFAICT).

    Sorry for being unclear, sure, object should be marked as initialized
    when they're returned from kmem_cache_alloc(). However, what I
    disagree with is *where* you're marking them as initialized. Surely
    they're not semantically initialized when the slabs are allocated
    (although technically they are).

    On Wed, Sep 3, 2008 at 8:08 AM, Steve VanDeBogart
    <vandebo-lkml@nerdbox.net> wrote:
    > Ideally, we'd tell Valgrind that the bytes of a free'd slab object are
    > no longer accessible, but the initialized state should remain the same
    > until the object is made accessible again by the next allocation of
    > the object. Unfortunately, the compression method for A & V bits in
    > Valgrind doesn't allow a region to be inaccessible and retain validness
    > bits.

    I don't see why you should mark them initialized all the time. Just
    mark them as uninitialized on kmem_cache_free() and again as
    initialized when they're about to be returned from kmem_cache_alloc()
    like we do in kmemcheck.

    Pekka


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