On 11/7/19 9:03 PM, Davidlohr Bueso wrote: > On Thu, 07 Nov 2019, Waiman Long wrote: >> With this patch applied, the customer is seeing significant performance >> improvement over the unpatched kernel. > > Could you give more details here? Red Hat has a customer that is running a transactional database workload. In this particular case, about ~500-1500GB of static hugepages are allocated. The database then allocates a single large shared memory segment in those hugepages to use primarily as a database buffer for 8kB blocks from disk (there are also other database structures in that shared memory, but it's mostly for buffer). Then thousands of separate processes reference and load data into that buffer. They were seeing multi-second pauses when starting up the database. I first gave them a patched kernel that disabled PMD sharing. That fixed their problem. After that, I gave them another test kernel that contained this patch. They said there were significant improved compared with the unpatched kernel. There is still some degradation compared to the kernel with huge shared pmd disabled entirely, but they're pretty close in performance. Cheer, Longman
