On Fri, Nov 29, 2019 at 03:18:01AM -0800, Matthew Wilcox wrote: >On Fri, Nov 29, 2019 at 04:30:02PM +0800, Wei Yang wrote: >> On Thu, Nov 28, 2019 at 02:39:04PM -0800, Matthew Wilcox wrote: >> >On Thu, Nov 28, 2019 at 09:09:45PM +0000, Wei Yang wrote: >> >> On Thu, Nov 28, 2019 at 11:31:43AM +0300, Kirill A. Shutemov wrote: >> >> >On Thu, Nov 28, 2019 at 09:03:21AM +0800, Wei Yang wrote: >> >> >> The check here is to guarantee pvmw->address iteration is limited in one >> >> >> page table boundary. To be specific, here the address range should be in >> >> >> one PMD_SIZE. >> >> >> >> >> >> If my understanding is correct, this check is already done in the above >> >> >> check: >> >> >> >> >> >> address >= __vma_address(page, vma) + PMD_SIZE >> >> >> >> >> >> The boundary check here seems not necessary. >> >> >> >> >> >> Signed-off-by: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx> >> >> > >> >> >NAK. >> >> > >> >> >THP can be mapped with PTE not aligned to PMD_SIZE. Consider mremap(). >> >> > >> >> >> >> Hi, Kirill >> >> >> >> Thanks for your comment during Thanks Giving Day. Happy holiday:-) >> >> >> >> I didn't think about this case before, thanks for reminding. Then I tried to >> >> understand your concern. >> >> >> >> mremap() would expand/shrink a memory mapping. In this case, probably shrink >> >> is in concern. Since pvmw->page and pvmw->vma are not changed in the loop, the >> >> case you mentioned maybe pvmw->page is the head of a THP but part of it is >> >> unmapped. >> > >> >mremap() can also move a mapping, see MREMAP_FIXED. >> >> Hi, Matthew >> >> Thanks for your comment. >> >> I took a look into the MREMAP_FIXED case, but still not clear in which case it >> fall into the situation Kirill mentioned. >> >> Per my understanding, move mapping is achieved in two steps: >> >> * unmap some range in old vma if old_len >= new_len >> * move vma >> >> If the length doesn't change, we are expecting to have the "copy" of old >> vma. This doesn't change the THP PMD mapping. >> >> So the change still happens in the unmap step, if I am correct. >> >> Would you mind giving me more hint on the case when we would have the >> situation as Kirill mentioned? > >Set up a THP mapping. >Move it to an address which is no longer 2MB aligned. >Unmap it. Thanks Matthew I got the point, thanks a lot :-) -- Wei Yang Help you, Help me
