On Thu, 24 May 2012, majianpeng wrote: > Hi all: > I readed a raid5,which size 30T.OS is RHEL6 32bit. > I reaed the raid5(as a whole,not parted) and found read address which not i wanted. > So I tested the newest kernel code,the problem is still. > I review the code, in function do_generic_file_read() > > index = *ppos >> PAGE_CACHE_SHIFT; > index is u32.and *ppos is long long. > So when *ppos is larger than 0xFFFF FFFF * PAGE_CACHE_SHIFT(16T Byte),then the index is error. > > I wonder this .In 32bit os ,block devices size do not large then 16T,in other words, if block devices larger than 16T,must parted. I am not surprised that the page cache limitation prevents you from reading the whole device with a 32-bit kernel. See MAX_LFS_FILESIZE in include/linux/fs.h. Our answer to that is just to use a 64-bit kernel. #if BITS_PER_LONG==32 #define MAX_LFS_FILESIZE (((u64)PAGE_CACHE_SIZE << (BITS_PER_LONG-1))-1) #elif BITS_PER_LONG==64 #define MAX_LFS_FILESIZE 0x7fffffffffffffffUL #endif But I am a little surprised that you get as far as 16TiB (with 4k page): I would have expected you to be stopped just before 8TiB (although I suspect that the limitation to 8TiB rather than 16TiB is unnecessary). And if I understand you correctly, read() or pread() gave you no error at those large offsets, but supplied data from the low offset instead? That does surprise me - have we missed a check there? Hugh -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>