On 08/01/2012 10:10 PM, Christoph Lameter wrote: > On Wed, 1 Aug 2012, Glauber Costa wrote: > >> I've audited all users of get_page() in the drivers/ directory for >> patterns like this. In general, they kmalloc something like a table of >> entries, and then get_page() the entries. The entries are either user >> pages, pages allocated by the page allocator, or physical addresses >> through their pfn (in 2 cases from the vga ones...) >> >> I took a look about some other instances where virt_to_page occurs >> together with kmalloc as well, and they all seem to fall in the same >> category. > > The case that was notorious in the past was a scsi control structure > allocated from slab that was then written to the device via DMA. And it > was not on x86 but some esoteric platform (powerpc?), > > A reference to the discussion of this issue in 2007: > > http://lkml.indiana.edu/hypermail/linux/kernel/0706.3/0424.html > Thanks. So again, I've scanned across that thread, and found some very useful excerpts from it, that can only argue in favor of my patch =) "There are no kmalloced pages. There is only kmalloced memory. You allocate pages from the page allocator. Its a layering violation to expect a page struct operation on a slab object to work." "So someone played loose ball with the slab, was successful and that makes it right now?" Looking at the code again, I see that page_mapping(), that ends up being called to do the translation in those pathological cases now features a VM_BUG_ON(), put in place by yourself. This dates back from 2007, giving me enough reason to believe that whatever issue still existed back then is already sorted out - or nobody really cares. -- 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>