linux-kernel - Re: [patch 1/2] mm, page_alloc: extend kernelcore and movablecore for percent

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Date:   Thu, 15 Feb 2018 09:49:00 -0600 (CST)
From:   Christopher Lameter <cl@...ux.com>
To:     Matthew Wilcox <willy@...radead.org>
cc:     Michal Hocko <mhocko@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jonathan Corbet <corbet@....net>,
        Vlastimil Babka <vbabka@...e.cz>, Mel Gorman <mgorman@...e.de>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-doc@...r.kernel.org
Subject: Re: [patch 1/2] mm, page_alloc: extend kernelcore and movablecore
 for percent

On Thu, 15 Feb 2018, Matthew Wilcox wrote:

> What if ... on startup, slab allocated a MAX_ORDER page for itself.
> It would then satisfy its own page allocation requests from this giant
> page.  If we start to run low on memory in the rest of the system, slab
> can be induced to return some of it via its shrinker.  If slab runs low
> on memory, it tries to allocate another MAX_ORDER page for itself.

The inducing of releasing memory back is not there but you can run SLUB
with MAX_ORDER allocations by passing "slab_min_order=9" or so on bootup.

> I think even this should reduce fragmentation.  We could enhance the
> fragmentation reduction by noticing when somebody else releases a page
> that was previously part of a slab MAX_ORDER page and handing that page
> back to slab.  When slab notices that it has an entire MAX_ORDER page free
> (and sufficient other memory on hand that it's unlikely to need it soon),
> it can hand that MAX_ORDER page back to the page allocator.

SLUB will release MAX_ORDER pages if they are completely free with the
above configuration.