On Sat, Aug 31, 2019 at 12:52:17AM +0800, Gao Xiang wrote: > Hi Christoph, > > On Fri, Aug 30, 2019 at 09:35:34AM -0700, Christoph Hellwig wrote: > > On Thu, Aug 15, 2019 at 12:41:51PM +0800, Gao Xiang wrote: > > > +static bool use_vmap; > > > +module_param(use_vmap, bool, 0444); > > > +MODULE_PARM_DESC(use_vmap, "Use vmap() instead of vm_map_ram() (default 0)"); > > > > And how would anyone know which to pick? > > It has significant FIO benchmark difference on sequential read least on arm64... > I have no idea whether all platform vm_map_ram() behaves better than vmap(), > so I leave an option for users here... vm_map_ram is supposed to generally behave better. So if it doesn't please report that that to the arch maintainer and linux-mm so that they can look into the issue. Having user make choices of deep down kernel internals is just a horrible interface. Please talk to maintainers of other bits of the kernel if you see issues and / or need enhancements.
