On Sat, Apr 16, 2016 at 04:41:33PM -0700, Hugh Dickins wrote: > The pmd_fault() method gives the filesystem an opportunity to place > a trans huge pmd entry at *pmd, before any pagetable is exposed (and > an opportunity to split it on COW fault): now use it for huge tmpfs. > > This patch is a little raw: with more time before LSF/MM, I would > probably want to dress it up better - the shmem_mapping() calls look > a bit ugly; it's odd to want FAULT_FLAG_MAY_HUGE and VM_FAULT_HUGE just > for a private conversation between shmem_fault() and shmem_pmd_fault(); > and there might be a better distribution of work between those two, but > prising apart that series of huge tests is not to be done in a hurry. > > Good for now, presents the new way, but might be improved later. > > This patch still leaves the huge tmpfs map_team_by_pmd() allocating a > pagetable while holding page lock, but other filesystems are no longer > doing so; and we've not yet settled whether huge tmpfs should (like anon > THP) or should not (like DAX) participate in deposit/withdraw protocol. > > Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx> Just for record: I don't like ->pmd_fault() approach because it results in two requests to file system (two shmem_fault() in this case) if we don't have a huge page to map: one for huge page (failed) and then one for small. I think this case should be rather common: all mounts without huge pages enabled. I expect performance regression from this too. -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>