linux-kernel - Re: slab: introduce the flag SLAB_MINIMIZE

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Message-ID: <alpine.DEB.2.20.1804171641390.20702@nuc-kabylake>
Date:   Tue, 17 Apr 2018 16:42:24 -0500 (CDT)
From:   Christopher Lameter <cl@...ux.com>
To:     Mikulas Patocka <mpatocka@...hat.com>
cc:     Vlastimil Babka <vbabka@...e.cz>,
        Mike Snitzer <snitzer@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Pekka Enberg <penberg@...nel.org>, linux-mm@...ck.org,
        dm-devel@...hat.com, David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: slab: introduce the flag SLAB_MINIMIZE_WASTE

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.