On Wed, Apr 25, 2018 at 10:13:53PM +0800, Yang Shi wrote: > Since tmpfs THP was supported in 4.8, hugetlbfs is not the only > filesystem with huge page support anymore. tmpfs can use huge page via > THP when mounting by "huge=" mount option. > > When applications use huge page on hugetlbfs, it just need check the > filesystem magic number, but it is not enough for tmpfs. Make > stat.st_blksize return huge page size if it is mounted by appropriate > "huge=" option to give applications a hint to optimize the behavior with > THP. > > Some applications may not do wisely with THP. For example, QEMU may mmap > file on non huge page aligned hint address with MAP_FIXED, which results > in no pages are PMD mapped even though THP is used. Some applications > may mmap file with non huge page aligned offset. Both behaviors make THP > pointless. > > statfs.f_bsize still returns 4KB for tmpfs since THP could be split, and it > also may fallback to 4KB page silently if there is not enough huge page. > Furthermore, different f_bsize makes max_blocks and free_blocks > calculation harder but without too much benefit. Returning huge page > size via stat.st_blksize sounds good enough. > > Since PUD size huge page for THP has not been supported, now it just > returns HPAGE_PMD_SIZE. > > Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx> > Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> > Cc: Hugh Dickins <hughd@xxxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxxxxx> > Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx> > Suggested-by: Christoph Hellwig <hch@xxxxxxxxxxxxx> Looks good to me: Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> -- Kirill A. Shutemov
