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    SubjectRe: [patch 1/3] slub: add per-cache slab thrash ratio
    On Mon, 30 Mar 2009, Christoph Lameter wrote:

    > > @@ -2291,10 +2292,13 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
    > > /*
    > > * Determine the number of objects per slab
    > > */
    > > + if (oo_objects(s->oo))
    > > + thrash_ratio = s->min_free_watermark * 100 / oo_objects(s->oo);
    > > s->oo = oo_make(order, size);
    >
    > s->oo is set *after* you check it. Check oo_objects after the value has
    > been set please.
    >

    It's actually right the way I implemented it, oo_objects(s->oo) will be 0
    when this is called for kmem_cache_open() meaning there is no preexisting
    slab_thrash_ratio. But this check is required when calculate_sizes() is
    called from order_store() to adjust the slab_thrash_ratio for the new
    objects per slab. The above check is saving the old thrash ratio so
    the new s->min_free_watermark value can be set following the
    oo_make(). This was mentioned in the changelog for this patch:

    The value is stored in terms of the number of objects that the
    ratio represents, not the ratio itself. This avoids costly
    arithmetic in the slowpath for a calculation that could otherwise
    be done only when `slab_thrash_ratio' or `order' is changed.


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