On Tue, Apr 13, 2010 at 6:09 PM, Patrick McHardy <kaber@xxxxxxxxx> wrote: > Changli Gao wrote: >> use hash table to speed up entry finding. >> >> If verdicts aren't received in order, list isn't efficient, and hash >> table is better. > > Any what is the advantage of using flex arrays compared to a simple > open code hash table? > >From Documentation/flexible-arrays.txt Large contiguous memory allocations can be unreliable in the Linux kernel. Kernel programmers will sometimes respond to this problem by allocating pages with vmalloc(). This solution not ideal, though. On 32-bit systems, memory from vmalloc() must be mapped into a relatively small address space; it's easy to run out. On SMP systems, the page table changes required by vmalloc() allocations can require expensive cross-processor interrupts on all CPUs. And, on all systems, use of space in the vmalloc() range increases pressure on the translation lookaside buffer (TLB), reducing the performance of the system. User may create lots of queues, which have large hash tables. Flex array has better scalability than vmalloc() and kmalloc(). -- Regards， Changli Gao(xiaosuo@xxxxxxxxx) -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
