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SubjectRe: Do we really need SLOB nowdays?
On Fri, Feb 18, 2022 at 10:13:29AM +0000, Hyeonggon Yoo wrote:
> On Wed, Dec 15, 2021 at 11:10:06AM +0100, Vlastimil Babka wrote:
> > 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.
>
> Just FYI...
> Some experiment based on v5.17-rc3:
>
> SLOB:
> Slab: 388 kB
>
> SLUB:
> Slab: 540 kB (+152kb)
>
> SLUB with s->min_partial = 0:
> Slab: 452 kB (+64kb)
>
> SLUB with s->min_partial = 0 && slub_max_order = 0:
> Slab: 436 kB (+48kb)
>
> SLUB with s->min_partial = 0 && slub_max_order = 0
> + merging slabs crazily (just ignore SLAB_NEVER_MERGE/SLAB_MERGE_SAME):
> Slab: 408 kB (+20kb)
>
> Decreasing further seem to be hard and
> I guess +20kb are due to partial slabs.
>
> I think SLUB can be memory-efficient as SLOB.
> Is SLOB (Address-Ordered next fit) stronger to fragmentation than SLUB?
(Address-Ordered *first* fit)

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