linux-kernel - Re: [PATCH 3/5] mm/slab: Do not call kmalloc

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Date:   Tue, 22 Feb 2022 19:59:08 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Hyeonggon Yoo <42.hyeyoo@...il.com>
Cc:     linux-mm@...ck.org, Roman Gushchin <guro@...com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>, linux-kernel@...r.kernel.org,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        David Rientjes <rientjes@...gle.com>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>
Subject: Re: [PATCH 3/5] mm/slab: Do not call kmalloc_large() for unsupported
 size

On Tue, Feb 22, 2022 at 08:10:32AM +0000, Hyeonggon Yoo wrote:
> On Mon, Feb 21, 2022 at 03:53:39PM +0000, Matthew Wilcox wrote:
> > On Mon, Feb 21, 2022 at 10:53:34AM +0000, Hyeonggon Yoo wrote:
> > > SLAB's kfree() does not support freeing an object that is allocated from
> > > kmalloc_large(). Fix this as SLAB do not pass requests larger than
> > > KMALLOC_MAX_CACHE_SIZE directly to page allocator.
> > 
> > I was wondering if we wanted to go in the other direction and get rid of
> > kmalloc cache sizes larger than, say, 64kB from the SLAB allocator.
> 
> Good point.
> 
> Hmm.. I don't think SLAB is benefiting from queueing that large objects,
> and maximum size is still limited to what buddy allocator supports.
> 
> I'll try reducing kmalloc caches up to order-1 page like SLUB.
> That would be easier to maintain.

If you have time to investigate these kinds of things, I think SLUB would
benefit from caching order-2 and order-3 slabs as well.  Maybe not so much
now that Mel included order-2 and order-3 caching in the page allocator.
But it'd be interesting to have numbers.