On Thu, 14 Apr 2016 10:48:29 -0600 Toshi Kani <toshi.k...@hpe.com> wrote:
> When CONFIG_FS_DAX_PMD is set, DAX supports mmap() using pmd page > size. This feature relies on both mmap virtual address and FS > block (i.e. physical address) to be aligned by the pmd page size. > Users can use mkfs options to specify FS to align block allocations. > However, aligning mmap address requires code changes to existing > applications for providing a pmd-aligned address to mmap(). > > For instance, fio with "ioengine=mmap" performs I/Os with mmap() [1]. > It calls mmap() with a NULL address, which needs to be changed to > provide a pmd-aligned address for testing with DAX pmd mappings. > Changing all applications that call mmap() with NULL is undesirable. > > This patch-set extends filesystems to align an mmap address for > a DAX file so that unmodified applications can use DAX pmd mappings. Matthew sounded unconvinced about the need for this patchset, but I must say that : The point is that we do not need to modify existing applications for using : DAX PMD mappings. : : For instance, fio with "ioengine=mmap" performs I/Os with mmap(). : https://github.com/caius/fio/blob/master/engines/mmap.c : : With this change, unmodified fio can be used for testing with DAX PMD : mappings. There are many examples like this, and I do not think we want : to modify all applications that we want to evaluate/test with. sounds pretty convincing? And if we go ahead with this, it looks like 4.7 material to me - it affects ABI and we want to get that stabilized asap. What do people think?
