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Date: Wed, 21 Mar 2018 13:58:39 -0500 (CDT)
From: Christopher Lameter <cl@linux.com>
Subject: Re: [PATCH] slab: introduce the flag SLAB_MINIMIZE_WASTE
In-Reply-To: <20180321185558.GA18494@bombadil.infradead.org>
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To: Matthew Wilcox <willy@infradead.org>
Cc: Mikulas Patocka <mpatocka@redhat.com>, Pekka Enberg <penberg@kernel.org>, David Rientjes <rientjes@google.com>, Joonsoo Kim <iamjoonsoo.kim@lge.com>, Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org, dm-devel@redhat.com, Mike Snitzer <msnitzer@redhat.com>

On Wed, 21 Mar 2018, Matthew Wilcox wrote:

> > Have a look at include/linux/mempool.h.
>
> That's not what mempool is for.  mempool is a cache of elements that were
> allocated from slab in the first place.  (OK, technically, you don't have
> to use slab as the allocator, but since there is no allocator that solves
> this problem, mempool doesn't solve the problem either!)

You can put the page allocator in there instead of a slab allocator.

> > But still the increased page order will get you into trouble with
> > fragmentation when the system runs for a long time. That is the reason we
> > try to limit the allocation sizes coming from the slab allocator.
>
> Right; he has a fallback already (vmalloc).  So ... let's just add the
> interface to allow slab caches to have their order tuned by users who
> really know what they're doing?

Ok thats trivial.