On 09/01/2015 02:10 PM, Kirill A. Shutemov wrote: > On Tue, Sep 01, 2015 at 01:54:26PM +0300, Boaz Harrosh wrote: >> On 09/01/2015 01:22 PM, Kirill A. Shutemov wrote: >>> For VM_PFNMAP and VM_MIXEDMAP we use vm_ops->pfn_mkwrite instead of >>> vm_ops->page_mkwrite to notify abort write access. This means we want >>> vma->vm_page_prot to be write-protected if the VMA provides this vm_ops. >>> >> >> Hi Kirill >> >> I will test with this right away and ACK on this. >> >> Hmm so are you saying we might be missing some buffer modifications right now. >> >> What would be a theoretical scenario that will cause these missed events? > > On writable mapping with vm_ops->pfn_mkwrite, but without > vm_ops->page_mkwrite: read fault followed by write access to the pfn. > Writable pte will be set up on read fault and write fault will not be > generated. > > I found it examining Dave's complain on generic/080: > > http://lkml.kernel.org/g/20150831233803.GO3902@dastard > > Although I don't think it's the reason. > >> I would like to put a test in our test rigs that should fail today and this >> patch fixes. >> >> [In our system every modified pmem block is also RDMAed to a remote >> pmem for HA, a missed modification will make the two copies unsynced] > > It shouldn't be a problem for ext2/ext4 as they provide both pfn_mkwrite > and page_mkwrite. > Ha right we have both as well, and so should xfs I think (because of the zero pages thing, in fact any dax.c user should). Thanks so this verifies why we could not see any such breakage. ACK-by: Boaz Harrosh <boaz@xxxxxxxxxxxxx> -- 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>