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Date: Tue, 17 Apr 2018 16:42:24 -0500 (CDT)
From: Christopher Lameter <cl@linux.com>
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To: Mikulas Patocka <mpatocka@redhat.com>
cc: Vlastimil Babka <vbabka@suse.cz>, Mike Snitzer <snitzer@redhat.com>,
        Matthew Wilcox <willy@infradead.org>,
        Pekka Enberg <penberg@kernel.org>, linux-mm@kvack.org,
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        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org
Subject: Re: slab: introduce the flag SLAB_MINIMIZE_WASTE
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On Tue, 17 Apr 2018, Mikulas Patocka wrote:

> > > The slub subsystem does actual fallback to low-order when the allocation
> > > fails (it allows different order for each slab in the same cache), but
> > > slab doesn't fallback and you get NULL if higher-order allocation fails.
> > > So, SLAB_MINIMIZE_WASTE is needed for slab because it will just randomly
> > > fail with higher order.
> >
> > Fix Slab instead of adding a flag that is only useful for one allocator?
>
> Slab assumes that all slabs have the same order, so it's not so easy to
> fix it.

Well since SLAB uses compound pages one could easily determine the order
of the page and thus also support multiple page orders there.