linux-kernel - Re: Do we really need SLOB nowdays?

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Message-ID: <54c6fff8-8c79-463b-a359-96e37bd13674@suse.cz>
Date:   Wed, 15 Dec 2021 11:10:06 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Hyeonggon Yoo <42.hyeyoo@...il.com>
Cc:     Christoph Lameter <cl@...two.org>,
        Matthew Wilcox <willy@...radead.org>,
        Christoph Lameter <cl@...two.de>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: Do we really need SLOB nowdays?

On 12/15/21 07:29, Hyeonggon Yoo wrote:
> On Tue, Dec 14, 2021 at 06:24:58PM +0100, Vlastimil Babka wrote:
>> On 12/10/21 13:06, Christoph Lameter wrote:
>> > On Fri, 10 Dec 2021, Hyeonggon Yoo wrote:
>> > 
>> >> > > (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.
>> > 
>> > What is the minimal size you need for SLUB?
>>  
> 
> I don't know why Christoph's mail is not in my mailbox. maybe I deleted it
> by mistake or I'm not cc-ed.
> 
> Anyway, I tried to measure this again with SLUB and SLOB.
> 
> SLUB uses few hundreds of bytes than SLOB.
> 
> There isn't much difference in 'Memory required to boot'.
> (interestingly SLUB requires less)
> 
> 'Memory required to boot' is measured by reducing memory
> until it says 'System is deadlocked on memory'. I don't know
> exact reason why they differ.
> 
> Note that the configuration is based on tinyconfig and
> I added initramfs support + tty layer (+ uart driver) + procfs support,
> + ELF binary support + etc.
> 
> there isn't even block layer, but it's good starting point to see
> what happens in small system.
> 
> SLOB:
> 
> 	Memory required to boot: 6950K
> 
> 		Slab:                368 kB
> 
> SLUB:
> 	Memory required to boot: 6800K
> 
> 		Slab:                552 kB
> 
> SLUB with slab merging:
> 
> 		Slab:                536 kB

168kB different on a system with less than 8MB memory looks rather
significant to me to simply delete SLOB, I'm afraid.