On Tue, Jan 17, 2023 at 10:34 AM Jann Horn <jannh@xxxxxxxxxx> wrote: > > On Mon, Jan 9, 2023 at 9:55 PM Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote: > > vma->lock being part of the vm_area_struct causes performance regression > > during page faults because during contention its count and owner fields > > are constantly updated and having other parts of vm_area_struct used > > during page fault handling next to them causes constant cache line > > bouncing. Fix that by moving the lock outside of the vm_area_struct. > > All attempts to keep vma->lock inside vm_area_struct in a separate > > cache line still produce performance regression especially on NUMA > > machines. Smallest regression was achieved when lock is placed in the > > fourth cache line but that bloats vm_area_struct to 256 bytes. > > Just checking: When you tested putting the lock in different cache > lines, did you force the slab allocator to actually store the > vm_area_struct with cacheline alignment (by setting SLAB_HWCACHE_ALIGN > on the slab or with a ____cacheline_aligned_in_smp on the struct > definition)? Yep, I tried all these combinations and still saw noticeable regression.
