On Wed, Oct 08, 2014 at 11:11:00PM +0300, Kirill A. Shutemov wrote: > On Wed, Oct 08, 2014 at 09:25:27AM -0400, Matthew Wilcox wrote: > > + pgoff = ((address - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff; > > + size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT; > > + if (pgoff >= size) > > + return VM_FAULT_SIGBUS; > > + /* If the PMD would cover blocks out of the file */ > > + if ((pgoff | PG_PMD_COLOUR) >= size) > > + return VM_FAULT_FALLBACK; > > IIUC, zero pading would work too. The blocks after this file might be allocated to another file already. I suppose we could ask the filesystem if it wants to allocate them to this file. Dave, Jan, is it acceptable to call get_block() for blocks that extend beyond the current i_size? > > + > > + memset(&bh, 0, sizeof(bh)); > > + block = ((sector_t)pgoff & ~PG_PMD_COLOUR) << (PAGE_SHIFT - blkbits); > > + > > + /* Start by seeing if we already have an allocated block */ > > + bh.b_size = PMD_SIZE; > > + length = get_block(inode, block, &bh, 0); > > This makes me confused. get_block() return zero on success, right? > Why the var called 'lenght'? Historical reasons. I can go back and change the name of the variable. > > + sector = bh.b_blocknr << (blkbits - 9); > > + length = bdev_direct_access(bh.b_bdev, sector, &kaddr, &pfn, bh.b_size); > > + if (length < 0) > > + goto sigbus; > > + if (length < PMD_SIZE) > > + goto fallback; > > + if (pfn & PG_PMD_COLOUR) > > + goto fallback; /* not aligned */ > > So, are you rely on pure luck to make get_block() allocate 2M aligned pfn? > Not really productive. You would need assistance from fs and > arch_get_unmapped_area() sides. Certainly ext4 and XFS will align their allocations; if you ask it for a 2MB block, it will try to allocate a 2MB block aligned on a 2MB boundary. I started looking into the get_unampped_area (and have the code sitting around to align specially marked files on special boundaries), but when I mentioned it to the author of the NVM Library, he said "Oh, I'll just pick a 1GB aligned area to request it be mapped at", so I haven't taken it any further. The upshot is that (confirmed with debugging code), when the tests run, they pretty much always get a correctly aligned block. -- 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>