From: Andrew Morton <akpm@linux-foundation.org>
To: David Rientjes <rientjes@google.com>
Cc: Christoph Lameter <cl@linux.com>,
Pekka Enberg <penberg@kernel.org>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [patch] mm, slab: avoid high-order slab pages when it does not reduce waste
Date: Fri, 12 Oct 2018 15:13:41 -0700 [thread overview]
Message-ID: <20181012151341.286cd91321cdda9b6bde4de9@linux-foundation.org> (raw)
In-Reply-To: <alpine.DEB.2.21.1810121424420.116562@chino.kir.corp.google.com>
On Fri, 12 Oct 2018 14:24:57 -0700 (PDT) David Rientjes <rientjes@google.com> wrote:
> The slab allocator has a heuristic that checks whether the internal
> fragmentation is satisfactory and, if not, increases cachep->gfporder to
> try to improve this.
>
> If the amount of waste is the same at higher cachep->gfporder values,
> there is no significant benefit to allocating higher order memory. There
> will be fewer calls to the page allocator, but each call will require
> zone->lock and finding the page of best fit from the per-zone free areas.
>
> Instead, it is better to allocate order-0 memory if possible so that pages
> can be returned from the per-cpu pagesets (pcp).
>
> There are two reasons to prefer this over allocating high order memory:
>
> - allocating from the pcp lists does not require a per-zone lock, and
>
> - this reduces stranding of MIGRATE_UNMOVABLE pageblocks on pcp lists
> that increases slab fragmentation across a zone.
Confused. Higher-order slab pages never go through the pcp lists, do
they? I'd have thought that by tending to increase the amount of
order-0 pages which are used by slab, such stranding would be
*increased*?
> We are particularly interested in the second point to eliminate cases
> where all other pages on a pageblock are movable (or free) and fallback to
> pageblocks of other migratetypes from the per-zone free areas causes
> high-order slab memory to be allocated from them rather than from free
> MIGRATE_UNMOVABLE pages on the pcp.
>
> mm/slab.c | 15 +++++++++++++++
Do slub and slob also suffer from this effect?
next prev parent reply other threads:[~2018-10-12 22:13 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-12 21:24 [patch] mm, slab: avoid high-order slab pages when it does not reduce waste David Rientjes
2018-10-12 22:13 ` Andrew Morton [this message]
2018-10-12 23:09 ` David Rientjes
2018-10-15 22:41 ` Christopher Lameter
2018-10-16 0:39 ` David Rientjes
2018-10-16 15:17 ` Christopher Lameter
2018-10-17 9:09 ` Vlastimil Babka
2018-10-17 15:38 ` Christopher Lameter
2018-10-15 22:42 ` Christopher Lameter
2018-10-16 8:42 ` Vlastimil Babka
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