Messages in this thread |  | | | Date | Wed, 3 Sep 2008 12:27:12 +0300 | | From | "Pekka Enberg" <> | | Subject | Re: [uml-devel] [PATCH 5/6] slab: Annotate slab |
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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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