On Tue, 3 Dec 2013, Andrew Morton wrote:
> > page = alloc_slab_page(alloc_gfp, node, oo);
> > if (unlikely(!page)) {
> > oo = s->min;
>
> What is the value of s->min? Please tell me it's zero.
It usually is.
> > @@ -1349,7 +1350,7 @@ static struct page *allocate_slab(struct kmem_cache
> > *s, gfp_t flags, int node)
> > && !(s->flags & (SLAB_NOTRACK | DEBUG_DEFAULT_FLAGS))) {
> > int pages = 1 << oo_order(oo);
> >
> > - kmemcheck_alloc_shadow(page, oo_order(oo), flags, node);
> > + kmemcheck_alloc_shadow(page, oo_order(oo), alloc_gfp, node);
>
> That seems reasonable, assuming kmemcheck can handle the allocation
> failure.
>
>
> Still I dislike this practice of using unnecessarily large allocations.
> What does it gain us? Slightly improved object packing density.
> Anything else?
The fastpath for slub works only within the bounds of a single slab page.
Therefore a larger frame increases the number of allocation possible from
the fastpath without having to use the slowpath and also reduces the
management overhead in the partial lists.
There is a kernel parameter that can be used to control the maximum order
slub_max_order
The default is PAGE_ALLOC_COSTLY_ORDER. See also
Documentation/vm/slub.txt.
Booting with slub_max_order=1 will force order 0/1 pages.
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