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

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Date:   Thu, 15 Feb 2018 12:48:17 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Christopher Lameter <cl@...ux.com>
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, Feb 15, 2018 at 09:49:00AM -0600, Christopher Lameter wrote:
> 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.

This is subtly different from the idea that I had.  If you set
slub_min_order to 9, then slub will allocate 2MB pages for each slab,
so allocating one object from kmalloc-32 and one object from dentry will
cause 4MB to be taken from the system.

What I was proposing was an intermediate page allocator where slab would
request 2MB for its own uses all at once, then allocate pages from that to
individual slabs, so allocating a kmalloc-32 object and a dentry object
would result in 510 pages of memory still being available for any slab
that needed it.