On Sun, Oct 17, 2021 at 01:57:08PM +0000, Hyeonggon Yoo wrote: > On Sun, Oct 17, 2021 at 01:36:18PM +0000, Hyeonggon Yoo wrote: > > On Sun, Oct 17, 2021 at 04:28:52AM +0000, Hyeonggon Yoo wrote: > > > I've been reading SLUB/SLOB code for a while. SLUB recently became > > > real time compatible by reducing its locking area. > > > > > > for now, SLUB is the only slab allocator for PREEMPT_RT because > > > it works better than SLAB on RT and SLOB uses non-deterministic method, > > > sequential fit. > > > > > > But memory usage of SLUB is too high for systems with low memory. > > > So In my local repository I made SLOB to use segregated free list > > > method, which is more more deterministic, to provide bounded latency. > > > > > > This can be done by managing list of partial pages globally > > > for every power of two sizes (8, 16, 32, ..., PAGE_SIZE) per NUMA nodes. > > > minimal allocation size is size of pointers to keep pointer of next free object > > > like SLUB. > > > > > > By making objects in same page to have same size, there's no > > > need to iterate free blocks in a page. (Also iterating pages isn't needed) > > > > > > Some cleanups and more tests (especially with NUMA/RT configs) needed, > > > but want to hear your opinion about the idea. Did not test on RT yet. > > > > > > Below is result of benchmarks and memory usage. (on !RT) > > > with 13% increase in memory usage, it's nine times faster and > > > bounded fragmentation, and importantly provides predictable execution time. > > > > > > > Hello linux-mm, I improved it and it uses lower memory > > and 9x~13x faster than original SLOB. it shows much less fragmentation > > after hackbench. > > > > Rather than managing global freelist that has power of 2 sizes, > > I made a kmem_cache to manage its own freelist (for each NUMA nodes) and > > Added support for slab merging. So It quite looks like a lightweight SLUB now. > > > > I'll send rfc patch after some testing and code cleaning. > > > > I think it is more RT-friendly becuase it's uses more deterministic > > algorithm (But lock is still shared among cpus). Any opinions for RT? > > Hi there. after some thinking, I got a new question: > If a lightweight SLUB is better than SLOB, > Do we really need SLOB nowdays? Better for what use case? SLOB is for machines with 1-16MB of RAM.
