On Sun, 16 Dec 2007 21:55:20 +0000 Mel Gorman wrote: > > > Just using cp to read the file is enough to cause problems but I included > > > a very basic program below that produces the BUG_ON checks. Is this a known > > > issue or am I using the interface incorrectly? > > > > I'd say you're using it correctly but you've found a hitherto unknown bug. > > On i386 highmem machines with CONFIG_HIGHPTE (at least) pte_offset_map() > > takes kmap_atomic(), so pagemap_pte_range() can't do copy_to_user() as it > > presently does. > > > > Drat. > > > > Still, that shouldn't really disrupt the testing which you're doing. You > > could disable CONFIG_HIGHPTE to shut it up. > > > > Yes, that did the trick. Using pagemap, it was trivial to show that the > 2.6.24-rc5-mm1 kernel was placing pages in reverse physical order like > the following output shows > > b: 32763 v: 753091 p: 65559 . 65558 contig: 1 > b: 32764 v: 753092 p: 65558 . 65557 contig: 1 > b: 32765 v: 753093 p: 65557 . 65556 contig: 1 > b: 32766 v: 753094 p: 65556 . 65555 contig: 1 > b: 32767 v: 753095 p: 65555 . 65555 contig: 1 > > p: is the PFN of the page v: is the page offset within an anonymous > mapping and b: is the number of non-contiguous blocks in the anonymous > mapping. With the patch applied, it looks more like; > > b: 1232 v: 752964 p: 58944 ................ 87328 contig: 15 > b: 1233 v: 752980 p: 87328 ................ 91200 contig: 15 > b: 1234 v: 752996 p: 91200 ................ 40272 contig: 15 > b: 1235 v: 753012 p: 40272 ................ 85664 contig: 15 > b: 1236 v: 753028 p: 85664 ................ 87312 contig: 15 > > so mappings are using contiguous pages again. This was the final test > program I used in case it's of any interest. > > Thanks > > /* > * showcontiguous.c > * > * Use the /proc/pid/pagemap interface to give an indication of how contiguous > * physical memory is in an anonymous virtual memory mapping > */ Matt, Did you ever make your python pagemap scripts available? If not, would you? --- ~Randy - To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
