On Mon, 14 May 2018, William Kucharski wrote: > The idea is that the kernel will attempt to allocate and map the range using a > PMD sized THP page upon first fault; if the allocation is successful the page > will be populated (at present using a call to kernel_read()) and the page will > be mapped at the PMD level. If memory allocation fails, the page fault routines > will drop through to the conventional PAGESIZE-oriented routines for mapping > the faulting page. Cool. This could be controlled by the faultaround logic right? If we get fault_around_bytes up to huge page size then it is reasonable to use a huge page direcly. fault_around_bytes can be set via sysfs so there is a natural way to control this feature there I think. > Since this approach will map a PMD size block of the memory map at a time, we > should see a slight uptick in time spent in disk I/O but a substantial drop in > page faults as well as a reduction in iTLB misses as address ranges will be > mapped with the larger page. Analysis of a test program that consists of a very > large text area (483,138,032 bytes in size) that thrashes D$ and I$ shows this > does occur and there is a slight reduction in program execution time. I think we would also want such a feature for regular writable pages as soon as possible.
