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    SubjectRe: [PATCH] slab: introduce kmem_cache_zalloc allocator
    Pekka J Enberg <penberg@cs.Helsinki.FI> wrote:
    > From: Pekka Enberg <>
    > This patch introduces a memory-zeroing variant of kmem_cache_alloc. The
    > allocator already exits in XFS and there are potential users for it so
    > this patch makes the allocator available for the general public.


    > + * kmem_cache_alloc - Allocate an object. The memory is set to zero.
    > + * @cache: The cache to allocate from.
    > + * @flags: See kmalloc().
    > + *
    > + * Allocate an object from this cache and set the allocated memory to zero.
    > + * The flags are only relevant if the cache has no available objects.
    > + */
    > +void *kmem_cache_zalloc(struct kmem_cache *cache, gfp_t flags)
    > +{
    > + void *ret = __cache_alloc(cache, flags, __builtin_return_address(0));
    > + if (ret)
    > + memset(ret, 0, obj_size(cache));
    > + return ret;
    > +}
    > +EXPORT_SYMBOL(kmem_cache_zalloc);

    The way this is supposed to work in slab is that the owner of the cache
    provides a constructor which zeroes out newly-allocated storage and the
    owner of the cache is supposed to free objects in a constructed (ie:
    zeroed) state.

    I've always felt that this was an odd design. Because

    a) All that cache-warmth which we get from the constructor's zeroing can
    be lost by the time we get around to using an individual object and

    b) The object may be cache-cold by the time we free it, and we'll take
    cache misses just putting it back into a constructed state for
    kmem_cache_free(). And we'll lose that cache warmth by the time we use
    this object again.

    So from that POV I think (in my simple way) that this is a good patch. But
    IIRC, Manfred has reasons why it might not be?
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      Last update: 2006-03-21 11:42    [W:0.032 / U:4.724 seconds]
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