On Thu, 2014-01-30 at 18:10 -0500, Mikulas Patocka wrote: > > On Thu, 30 Jan 2014, James Bottomley wrote: > > > Why is this? the whole reason for CONFIG_LBDAF is supposed to be to > > allow 64 bit offsets for block devices on 32 bit. It sounds like > > there's somewhere not using sector_t ... or using it wrongly which needs > > fixing. > > The page cache uses unsigned long as a page index. Therefore, if unsigned > long is 32-bit, the block device may have at most 2^32-1 pages. Um, that's the index into the mapping, not the device; a device can have multiple mappings and each mapping has a radix tree of pages. For most filesystems a mapping is equivalent to a file, so we can have large filesystems, but they can't have files over actually 4GB on 32 bits otherwise mmap fails. Are we running into a problems with struct address_space where we've assumed the inode belongs to the file and lvm is doing something where it's the whole device? > > > On 32-bit architectures, we must limit block device size to > > > PAGE_SIZE*(2^32-1). > > > > So you're saying CONFIG_LBDAF can never work, why? > > > > James > > CONFIG_LBDAF works, but it doesn't allow unlimited capacity: on x86, > without CONFIG_LBDAF, the limit is 2TiB. With CONFIG_LBDAF, the limit is > 16TiB (4096*2^32). I don't think the people who did the large block device work expected to gain only 3 bits for all their pain. James -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
