On Thu, 1 Nov 2012, Dave Jones wrote: > On Wed, Oct 24, 2012 at 09:36:27PM -0700, Hugh Dickins wrote: > > On Wed, 24 Oct 2012, Dave Jones wrote: > > > > > Machine under significant load (4gb memory used, swap usage fluctuating) > > > triggered this... > > > > > > WARNING: at mm/shmem.c:1151 shmem_getpage_gfp+0xa5c/0xa70() > > > > > > 1148 error = shmem_add_to_page_cache(page, mapping, index, > > > 1149 gfp, swp_to_radix_entry(swap)); > > > 1150 /* We already confirmed swap, and make no allocation */ > > > 1151 VM_BUG_ON(error); > > > 1152 } > > > > That's very surprising. Easy enough to handle an error there, but > > of course I made it a VM_BUG_ON because it violates my assumptions: > > I rather need to understand how this can be, and I've no idea. > > I just noticed we had a user report hitting this same warning, but > with a different trace.. > > : [<ffffffff8105b84f>] warn_slowpath_common+0x7f/0xc0 > : [<ffffffff8105b8aa>] warn_slowpath_null+0x1a/0x20 > : [<ffffffff81143c73>] shmem_getpage_gfp+0x7f3/0x830 > : [<ffffffff81158c9d>] ? vma_adjust+0x3ed/0x620 > : [<ffffffff81143f02>] shmem_file_aio_read+0x1f2/0x380 > : [<ffffffff8118e487>] do_sync_read+0xa7/0xe0 > : [<ffffffff8118eda9>] vfs_read+0xa9/0x180 > : [<ffffffff8118eeca>] sys_read+0x4a/0x90 > : [<ffffffff816226e9>] system_call_fastpath+0x16/0x1b Equally explicable by Hannes's hypothesis; but useful supporting evidence, thank you. Except... earlier in the thread you explained how you hacked #define VM_BUG_ON(cond) WARN_ON(cond) to get this to come out as a warning instead of a bug, and now it looks as if "a user" has here done the same. Which is very much a user's right, of course; but does make me wonder whether that user might actually be davej ;) Never mind, whatever, it's more justification for the fix - which I've honestly not forgotten, but somehow not got around to sending (with a couple of others even longer outstanding). On its way shortly, for some unpredictable value of shortly. 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>