On Tue, 20 Jan 2009, Zhang, Yanmin wrote: > kmem_cache skbuff_head_cache's object size is just 256, so it shares the kmem_cache > with :0000256. Their order is 1 which means every slab consists of 2 physical pages. That order can be changed. Try specifying slub_max_order=0 on the kernel command line to force an order 0 alloc. The queues of the page allocator are of limited use due to their overhead. Order-1 allocations can actually be 5% faster than order-0. order-0 makes sense if pages are pushed rapidly to the page allocator and are then reissues elsewhere. If there is a linear consumption then the page allocator queues are just overhead. > Page allocator has an array at zone_pcp(zone, cpu)->pcp to keep a page buffer for page order 0. > But here skbuff_head_cache's order is 1, so UDP-U-4k couldn't benefit from the page buffer. That usually does not matter because of partial list avoiding page allocator actions. > SLQB has no such issue, because: > 1) SLQB has a percpu freelist. Free objects are put to the list firstly and can be picked up > later on quickly without lock. A batch parameter to control the free object recollection is mostly > 1024. > 2) SLQB slab order mostly is 0, so although sometimes it calls alloc_pages/free_pages, it can > benefit from zone_pcp(zone, cpu)->pcp page buffer. > > So SLUB need resolve such issues that one process allocates a batch of objects and another process > frees them batchly. SLUB has a percpu freelist but its bounded by the basic allocation unit. You can increase that by modifying the allocation order. Writing a 3 or 5 into the order value in /sys/kernel/slab/xxx/order would do the trick.
