Messages in this thread |  | | | Date | Tue, 13 Jul 2010 15:40:25 +0900 | | From | KAMEZAWA Hiroyuki <> | | Subject | Re: [RFC] Tight check of pfn_valid on sparsemem |
| |
On Tue, 13 Jul 2010 15:04:00 +0900 Minchan Kim <minchan.kim@gmail.com> wrote:
> >> > 2. This can't be help for a case where a section has multiple small holes. > >> > >> I agree. But this(not punched hole but not filled section problem) > >> isn't such case. But it would be better to handle it altogether. :) > >> > >> > > >> > Then, my proposal for HOLES_IN_MEMMAP sparsemem is below. > >> > == > >> > Some architectures unmap memmap[] for memory holes even with SPARSEMEM. > >> > To handle that, pfn_valid() should check there are really memmap or not. > >> > For that purpose, __get_user() can be used. > >> > >> Look at free_unused_memmap. We don't unmap pte of hole memmap. > >> Is __get_use effective, still? > >> > > __get_user() works with TLB and page table, the vaddr is really mapped or not. > > If you got SEGV, __get_user() returns -EFAULT. It works per page granule. > > I mean following as. > For example, there is a struct page in on 0x20000000. > > int pfn_valid_mapped(unsigned long pfn) > { > struct page *page = pfn_to_page(pfn); /* hole page is 0x2000000 */ > char *lastbyte = (char *)(page+1)-1; /* lastbyte is 0x2000001f */ > char byte; > > /* We pass this test since free_unused_memmap doesn't unmap pte */ > if(__get_user(byte, page) != 0) > return 0;
why ? When the page size is 4096 byte.
0x1ffff000 - 0x1ffffffff 0x20000000 - 0x200000fff are on the same page. And memory is mapped per page. What we access by above __get_user() is a byte at [0x20000000, 0x20000001) and it's unmapped if 0x20000000 is unmapped. Thanks, -Kame
-- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
|  |