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    Subject[TRIVIAL] implement kmem_cache_size
    Date
    From:  Christoph Hellwig <hch@lst.de>

    Currently there is no way to find out the effective object size of a slab
    cache. XFS has lots of IRIX-derived code that want to do zalloc() style
    allocations on zones (which are implemented as slab caches in XFS/Linux)
    and thus needs to know about it. There are three ways do implement it:

    a) implement kmem_cache_zalloc
    b) make the xfs zone a struct of kmem_cache_t and a size variable
    c) implement kmem_cache_size

    The current XFS tree does a) but I absolutely don't like it as encourages
    people to use kmem_cache_zalloc for new code instead of thinking about
    how to utilize slab object reuse. b) would be easy, but I guess
    kmem_cache_size is usefull enough to get into the kernel.

    Trivial patch to implement kmem_cache_size (doesn't change any existing
    code) appended:



    --- trivial-2.5.28/include/linux/slab.h.orig Fri Jul 26 16:37:00 2002
    +++ trivial-2.5.28/include/linux/slab.h Fri Jul 26 16:37:00 2002
    @@ -57,6 +57,7 @@
    extern int kmem_cache_shrink(kmem_cache_t *);
    extern void *kmem_cache_alloc(kmem_cache_t *, int);
    extern void kmem_cache_free(kmem_cache_t *, void *);
    +extern unsigned int kmem_cache_size(kmem_cache_t *);

    extern void *kmalloc(size_t, int);
    extern void kfree(const void *);
    --- trivial-2.5.28/kernel/ksyms.c.orig Fri Jul 26 16:37:00 2002
    +++ trivial-2.5.28/kernel/ksyms.c Fri Jul 26 16:37:00 2002
    @@ -105,6 +105,7 @@
    EXPORT_SYMBOL(kmem_cache_shrink);
    EXPORT_SYMBOL(kmem_cache_alloc);
    EXPORT_SYMBOL(kmem_cache_free);
    +EXPORT_SYMBOL(kmem_cache_size);
    EXPORT_SYMBOL(kmalloc);
    EXPORT_SYMBOL(kfree);
    EXPORT_SYMBOL(vfree);
    --- trivial-2.5.28/mm/slab.c.orig Fri Jul 26 16:37:00 2002
    +++ trivial-2.5.28/mm/slab.c Fri Jul 26 16:37:00 2002
    @@ -1647,6 +1647,15 @@
    local_irq_restore(flags);
    }

    +unsigned int kmem_cache_size(kmem_cache_t *cachep)
    +{
    +#if DEBUG
    + if (cachep->flags & SLAB_RED_ZONE)
    + return (cachep->objsize - 2*BYTES_PER_WORD);
    +#endif
    + return cachep->objsize;
    +}
    +
    kmem_cache_t * kmem_find_general_cachep (size_t size, int gfpflags)
    {
    cache_sizes_t *csizep = cache_sizes;
    --
    Don't blame me: the Monkey is driving
    -
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