Message-ID: <54c6fff8-8c79-463b-a359-96e37bd13674@suse.cz>
Date:   Wed, 15 Dec 2021 11:10:06 +0100
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.4.0
Subject: Re: Do we really need SLOB nowdays?
Content-Language: en-US
To:     Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc:     Christoph Lameter <cl@gentwo.org>,
        Matthew Wilcox <willy@infradead.org>,
        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>
References: <20211017133618.GA7989@kvm.asia-northeast3-a.c.our-ratio-313919.internal>
 <20211017135708.GA8442@kvm.asia-northeast3-a.c.our-ratio-313919.internal>
 <YWw1n6y/AGED14HD@casper.infradead.org>
 <CAB=+i9Tor-tmZuB8YjATT_rv68nnF2W_TvMvyGp55AGaSyKynw@mail.gmail.com>
 <alpine.DEB.2.22.394.2110251016260.3145@gentwo.de>
 <20211028100414.GA2928@kvm.asia-northeast3-a.c.our-ratio-313919.internal>
 <YXqSoo+b9RTclW/2@casper.infradead.org> <20211210110835.GA632811@odroid>
 <alpine.DEB.2.22.394.2112101305500.290446@gentwo.de>
 <cbfaeb40-13c7-15b6-177d-07b3f3c4a0a9@suse.cz>
 <20211215062904.GA1150813@odroid>
From:   Vlastimil Babka <vbabka@suse.cz>
In-Reply-To: <20211215062904.GA1150813@odroid>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

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.