Hi Mel, Sorry for the formatting. I forgot to include the following entire backtrace: #> cp test_huge_file nfsmnt kernel BUG at mm/page_alloc.c:849! Unable to handle kernel NULL pointer dereference at virtual address 00000000 pgd = ce9f0000 <SNIP> Backtrace: [<c00269ac>] (__bug+0x0/0x30) from [<c008e8b0>] (move_freepages_block+0xd4/0x158) [<c008e7dc>] (move_freepages_block+0x0/0x158) from [<c008eb10>] (__rmqueue+0x1dc/0x32c) r8:c0481120 r7:c048107c r6:00000003 r5:00000001 r4:c04f8200 r3:00000000 [<c008e934>] (__rmqueue+0x0/0x32c) from [<c00906f8>] (get_page_from_freelist+0x12c/0x530) [<c00905cc>] (get_page_from_freelist+0x0/0x530) from [<c0090bec>] (__alloc_pages_nodemask+0xf0/0x544) [<c0090afc>] (__alloc_pages_nodemask+0x0/0x544) from [<c00b4da4>] (cache_alloc_refill+0x2d0/0x654) [<c00b4ad4>] (cache_alloc_refill+0x0/0x654) from [<c00b5258>] (kmem_cache_alloc+0x58/0x9c) [<c00b5200>] (kmem_cache_alloc+0x0/0x9c) from [<c01f0154>] (radix_tree_preload+0x58/0xbc) r7:00006741 r6:000000d0 r5:c04a98a0 r4:ce986000 [<c01f00fc>] (radix_tree_preload+0x0/0xbc) from [<c008ac94>] (add_to_page_cache_locked+0x20/0x1c4) r6:ce987d20 r5:ce346c1c r4:c04f8600 r3:000000d0 [<c008ac74>] (add_to_page_cache_locked+0x0/0x1c4) from [<c008ae84>] (add_to_page_cache_lru+0x4c/0x7c) r8:00000020 r7:ce7402a0 r6:ce987d20 r5:00000005 r4:c04f8600 r3:000000d0 [<c008ae38>] (add_to_page_cache_lru+0x0/0x7c) from [<c00e8428>] (mpage_readpages+0x7c/0x108) r5:00000005 r4:c04f8600 [<c00e83ac>] (mpage_readpages+0x0/0x108) from [<c010f450>] (fat_readpages+0x20/0x28) [<c010f430>] (fat_readpages+0x0/0x28) from [<c0092ebc>] (__do_page_cache_readahead+0x1c4/0x27c) [<c0092cf8>] (__do_page_cache_readahead+0x0/0x27c) from [<c0092fa0>] (ra_submit+0x2c/0x34) [<c0092f74>] (ra_submit+0x0/0x34) from [<c0093294>] (ondemand_readahead+0x20c/0x21c) [<c0093088>] (ondemand_readahead+0x0/0x21c) from [<c0093348>] (page_cache_async_readahead+0xa4/0xd8) [<c00932a4>] (page_cache_async_readahead+0x0/0xd8) from [<c008c6f4>] (generic_file_aio_read+0x360/0x7f4) r8:00000000 r7:ce346c1c r6:ce88dba0 r5:0000671c r4:c04f9640 [<c008c394>] (generic_file_aio_read+0x0/0x7f4) from [<c00b7954>] (do_sync_read+0xa0/0xd8) [<c00b78b4>] (do_sync_read+0x0/0xd8) from [<c00b84d8>] (vfs_read+0xb8/0x154) r6:bed53650 r5:ce88dba0 r4:00001000 [<c00b8420>] (vfs_read+0x0/0x154) from [<c00b863c>] (sys_read+0x44/0x70) r8:0671c000 r7:00000003 r6:00001000 r5:bed53650 r4:ce88dba0 [<c00b85f8>] (sys_read+0x0/0x70) from [<c0022f80>] (ret_fast_syscall+0x0/0x30) r9:ce986000 r8:c0023128 r6:bed53650 r5:00001000 r4:0013a4e0 Code: e59f0010 e1a01003 eb0d0852 e3a03000 (e5833000) <SNIP> Since I was testing on linux-2.6.35.9, line 849 in page_alloc.c is the same line as you have mentioned: BUG_ON(page_zone(start_page) != page_zone(end_page)) I reproduce this crash by altering the memory banks' memory ranges such that they are not aligned to the SECTION_SIZE_BITS size. For example, on my ARM system SECTION_SIZE_BITS is 23(8MB), so I change the code in arch/arm/mach-* code so that the total kernel memory size in the memory banks is lesser by 1 MB, which makes the total kernel memory size become not exactly divisible by 8 MB. Thanks, Kautuk. On Wed, Aug 3, 2011 at 4:35 PM, Mel Gorman <mgorman@xxxxxxx> wrote: > On Tue, Aug 02, 2011 at 05:38:31PM +0530, Kautuk Consul wrote: >> Hi, >> >> In the case where the total kernel memory is not aligned to the >> SECTION_SIZE_BITS I see a kernel crash. >> >> When I copy a huge file, then the kernel crashes at the following callstack: >> > > The callstack should not be 80-column formatted as this is completely > manged and unreadable without manual editting. Also, why did you not > include the full error message? With it, I'd have a better idea of > which bug check you hit. > >> Backtrace: >> <SNIP> >> >> The reason for this is that the CONFIG_HOLES_IN_ZONE configuration >> option is not automatically enabled when SPARSEMEM or >> ARCH_HAS_HOLES_MEMORYMODEL are enabled. Due to this, the >> pfn_valid_within() macro always returns 1 due to which the BUG_ON is >> encountered. >> This patch enables the CONFIG_HOLES_IN_ZONE config option if either >> ARCH_HAS_HOLES_MEMORYMODEL or SPARSEMEM is enabled. >> >> Although I tested this on an older kernel, i.e., 2.6.35.13, I see that >> this option has not been enabled as yet in linux-3.0 and this appears >> to be a >> logically correct change anyways with respect to pfn_valid_within() >> functionality. >> > > There is a performance cost associated with HOLES_IN_ZONE which may be > offset by memory savings but not necessarily. > > If the BUG_ON you are hitting is this one > BUG_ON(page_zone(start_page) != page_zone(end_page)) then I'd be > wondering why the check in move_freepages_block() was insufficient. > > If it's because holes are punched in the memmap then the option does > need to be set. > > -- > Mel Gorman > SUSE Labs > -- 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>