Date:   Fri, 10 Dec 2021 11:08:35 +0000
From:   Hyeonggon Yoo <42.hyeyoo@gmail.com>
To:     Matthew Wilcox <willy@infradead.org>
Cc:     Christoph Lameter <cl@gentwo.de>,
        Linux Memory Management List <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Vlastimil Babka <vbabka@suse.cz>
Subject: Re: Do we really need SLOB nowdays?
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On Thu, Oct 28, 2021 at 01:08:02PM +0100, Matthew Wilcox wrote:
> On Thu, Oct 28, 2021 at 10:04:14AM +0000, Hyeonggon Yoo wrote:
> > On Mon, Oct 25, 2021 at 10:17:08AM +0200, Christoph Lameter wrote:
> > > On Mon, 18 Oct 2021, Hyeonggon Yoo wrote:
> > > 
> > > > > Better for what use case?  SLOB is for machines with 1-16MB of RAM.
> > > > >
> > > >
> > > > 1~16M is smaller than I thought. Hmm... I'm going to see how it works on
> > > > tiny configuration. Thank you Matthew!
> > > 
> > > Is there any reference where we can see such a configuration? Sure it does
> > > not work with SLUB too?
> > 
> > I thought why Matthew said "SLOB is for machines with 1-16MB of RAM"
> > is because if memory is so low, then it is sensitive to memory usage.
> > 
> > (But I still have doubt if we can run linux on machines like that.)
> 
> I sent you a series of articles about making Linux run in 1MB.

After some time playing with the size of kernel,
I was able to run linux in 6.6MiB of RAM. and the SLOB used
around 300KiB of memory.

Running linux in 1MiB seems almost impossible without introducing
XIP (eXecute In Place) which executes binary directly from ROM or Flash.
(and that's actually not reducing kernel size, it's reducing RAM required to boot)

SLOB seems to be useful when the machine has really really tiny memory.
because the slab allocator can use most of memory when the memory is so
small. But if the machine has some megabytes of RAM,
I think SLUB is right allocator to choose.

Thank you for sending that link.
it was so nice article.