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? Good question. Meanwhile I tried to compare Slab: in /proc/meminfo on a virtme run: virtme-run --mods=auto --kdir /home/vbabka/wrk/linux/ --memory 2G,slots=2,maxmem=4G --qemu-opts --smp 4 Got ~30800kB with SLOB, 34500kB with SLUB without DEBUG and PERCPU_PARTIAL. Then did a quick and dirty patch (below) to never load c->slab in ___slab_alloc() and got to 32200kB. Fiddling with slub_min_order/slub_max_order didn't actually help, probably due to causing more internal fragmentation. So that's relatively close, but on a really small system the difference can be possibly more prominent. Also my test doesn't account for text/data or percpu usage differences. diff --git a/mm/slub.c b/mm/slub.c index 68aa112e469b..fd9c853971d1 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -3054,6 +3054,8 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node, */ goto return_single; + goto return_single; + retry_load_slab: local_lock_irqsave(&s->cpu_slab->lock, flags);
