"Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx> writes: > [ text/plain ] > On Mon, Mar 21, 2016 at 10:03:29AM +0530, Aneesh Kumar K.V wrote: >> "Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx> writes: >> >> > [ text/plain ] >> > On Fri, Mar 18, 2016 at 07:23:41PM +0530, Aneesh Kumar K.V wrote: >> >> "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> writes: >> >> >> >> > [ text/plain ] >> >> > split_huge_pmd() for file mappings (and DAX too) is implemented by just >> >> > clearing pmd entry as we can re-fill this area from page cache on pte >> >> > level later. >> >> > >> >> > This means we don't need deposit page tables when file THP is mapped. >> >> > Therefore we shouldn't try to withdraw a page table on zap_huge_pmd() >> >> > file THP PMD. >> >> >> >> Archs like ppc64 use deposited page table to track the hardware page >> >> table slot information. We probably may want to add hooks which arch can >> >> use to achieve the same even with file THP >> > >> > Could you describe more on what kind of information you're talking about? >> > >> >> Hardware page table in ppc64 requires us to map each subpage of the huge >> page. This is needed because at low level we use segment base page size >> to find the hash slot and on TLB miss, we use the faulting address and >> base page size (which is 64k even with THP) to find whether we have >> the page mapped in hash page table. Since we use base page size of 64K, >> we need to make sure that subpages are mapped (on demand) in hash page >> table. If we have then mapped we also need to track their hash table >> slot information so that we can clear it on invalidate of hugepage. >> >> With THP we used the deposited page table to store the hash slot >> information. > > Could you prepare the patch with these hooks so we can discuss it details? > I still have hard time wrap my had around this. ok > > I think you have the same problem with DAX huge pages. Or you don't care > about DAX? > Yes, DAX hugepage will not be working on ppc64. It is there in the TODO list to get it working :). -aneesh -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
