On Thu, Oct 21, 2021 at 07:36:26PM +0200, Vlastimil Babka wrote: > On 10/20/21 13:46, Hyeonggon Yoo wrote: > > On Sun, Oct 17, 2021 at 08:38:41PM -0700, Rustam Kovhaev wrote: > >> Let's prepend all allocations of (PAGE_SIZE - align_offset) and less > >> with the size header. This way kmem_cache_alloc() memory can be freed > >> with kfree() and the other way around, as long as they are less than > >> (PAGE_SIZE - align_offset). > > > > Hello Rustam, I measured its impact on memory usage on > > tiny kernel configuration as SLOB is used in very small machine. > > > > on x86 32 bit + tinyconfig: > > Before: > > Slab: 668 kB > > > > After: > > Slab: 688~692 kB > > > > it adds 20~24kB. > > Thanks for the measurement. That's 3.5% increase. > You're welcome. > > > >> > >> The main reason for this change is to simplify SLOB a little bit, make > >> it a bit easier to debug whenever something goes wrong. > >> > > > > It seems acceptable But I wonder it is worth to increase memory usage > > to allow freeing kmem_cache_alloc-ed objects by kfree()? > > Not for the reason above, but for providing a useful API guarantee > regardless of selected slab allocator IMHO yes. > Mm.. that means some callers free kmem_cache_alloc-ed object using kfree, and SLAB/SLUB already support that, and SLOB doesn't. In what situations is freeing using kfree needed? Wouldn't this make code confusing? > > Thanks, > > Hyeonggon > > > >> meminfo right after the system boot, without the patch: > >> Slab: 35500 kB > >> > >> the same, with the patch: > >> Slab: 36396 kB > >> > > >
