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    SubjectRe: [RFC 0/3] Slab Defrag / Slab Targeted Reclaim and general Slab API changes
    On Sat, 5 May 2007, Eric Dumazet wrote:

    > > C. Introduces a slab_ops structure that allows a slab user to provide
    > > operations on slabs.
    >
    > Could you please make it const ?

    Sure. Done.

    > > All of this is really not necessary since the compiler knows how to align
    > > structures and we should use this information instead of having the user
    > > specify an alignment. I would like to get rid of SLAB_HWCACHE_ALIGN
    > > and kmem_cache_create. Instead one would use the following macros (that
    > > then result in a call to __kmem_cache_create).
    >
    > Hum, the problem is the compiler sometimes doesnt know the target processor
    > alignment.
    >
    > Adding ____cacheline_aligned to 'struct ...' definitions might be overkill if
    > you compile a generic kernel and happens to boot a Pentium III with it.

    Then add ___cacheline_aligned_in_smp or specify the alignment in the
    various other ways that exist. Practice is that most slabs specify
    SLAB_HWCACHE_ALIGN. So most slabs are cache aligned today.

    > G. Being able to track the number of pages in a kmem_cache
    >
    >
    > If you look at fs/buffer.c, you'll notice the bh_accounting, recalc_bh_state()
    > that might be overkill for large SMP configurations, when the real concern is
    > to be able to limit the bh's not to exceed 10% of LOWMEM.
    >
    > Adding a callback in slab_ops to track total number of pages in use by a given
    > kmem_cache would be good.

    Such functionality exists internal to SLUB and in the reporting tool.
    I can export that function if you need it.

    > Same thing for fs/file_table.c : nr_file logic
    > (percpu_counter_dec()/percpu_counter_inc() for each file open/close) could be
    > simplified if we could just count the pages in use by filp_cachep kmem_cache.
    > The get_nr_files() thing is not worth the pain.

    Sure. What exactly do you want? The absolute number of pages of memory
    that the slab is using?

    kmem_cache_pages_in_use(struct kmem_cache *) ?

    The call will not be too lightweight since we will have to loop over all
    nodes and add the counters in each per node struct for allocates slabs.

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