> I've recently been trying to track down the root cause of my server's > persistent issue of thrashing horribly after being left inactive. It > seems that the issue is likely my nightly backup schedule (using rsync) > which traverses my entire 50GB home directory. I was surprised to find > that rsync does not use fadvise to notify the kernel of its use-once > data usage pattern. > > It looks like a patch[1] was written (although never merged, it seems) > incorporating fadvise support, but I found its implementation rather > odd, using mincore() and FADV_DONTNEED to kick out only regions brought > in by rsync. It seemed to me the simpler and more appropriate solution > would be to simply flag every touched file with FADV_NOREUSE and let the > kernel manage automatically expelling used pages. > > After looking deeper into the kernel implementation[2] of fadvise() the > reason for using DONTNEED became more apparant. It seems that the kernel > implements NOREUSE as a noop. A little googling revealed[3] that I not > the first person to encounter this limitation. It looks like a few > folks[4] have discussed addressing the issue in the past, but nothing > has happened as of 2.6.36. Are there plans to implement this > functionality in the near future? It seems like the utility of fadvise > is severely limited by lacking support for NOREUSE. btw, Other OSs seems to also don't implement it. example, http://src.opensolaris.org/source/xref/onnv/onnv-gate/usr/src/lib/libc/port/gen/posix_fadvise.c 35 /* 36 * SUSv3 - file advisory information 37 * 38 * This function does nothing, but that's OK because the 39 * Posix specification doesn't require it to do anything 40 * other than return appropriate error numbers. 41 * 42 * In the future, a file system dependent fadvise() or fcntl() 43 * interface, similar to madvise(), should be developed to enable 44 * the kernel to optimize I/O operations based on the given advice. 45 */ 46 47 /* ARGSUSED1 */ 48 int 49 posix_fadvise(int fd, off_t offset, off_t len, int advice) 50 { 51 struct stat64 statb; 52 53 switch (advice) { 54 case POSIX_FADV_NORMAL: 55 case POSIX_FADV_RANDOM: 56 case POSIX_FADV_SEQUENTIAL: 57 case POSIX_FADV_WILLNEED: 58 case POSIX_FADV_DONTNEED: 59 case POSIX_FADV_NOREUSE: 60 break; 61 default: 62 return (EINVAL); 63 } 64 if (len < 0) 65 return (EINVAL); 66 if (fstat64(fd, &statb) != 0) 67 return (EBADF); 68 if (S_ISFIFO(statb.st_mode)) 69 return (ESPIPE); 70 return (0); 71 } So, I don't think application developers will use fadvise() aggressively because we don't have a cross platform agreement of a fadvice behavior. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>