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

> > > + 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.

Then its the wrong place to set it. Initializations are done in
kmem_cache_open() after calculate_sizes are called.


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