H. Peter Anvin wrote: > Really (pae ? 2M : 1M), in other words, plus the 128K for bootmem. > Note that this is creating page tables for, not erasing. To map 2M, > we will only use 2K of additional memory (meaning there is 50% chance > we end up using an additional 4K page.) > > So the solution is simply to change INIT_MAP_BEYOND_END in head.S > appropriately. Like this? Should we bother adding some slop pages for allocations which happen before paging_init()?
Subject: i386: map enough initial memory to create lowmem mappings head.S creates the very initial pagetable for the kernel. This just maps enough space for the kernel itself, and an allocation bitmap. The amount of mapped memory is rounded up to 4Mbytes, and so this typically ends up mapping 8Mbytes of memory. When booting, pagetable_init() needs to create mappings for all lowmem, and the pagetables for these mappings are allocated from the free pages around the kernel in low memory. If the number of pagetable pages + kernel size exceeds head.S's initial mapping, it will end up faulting on an unmapped page. This will only happen with specific combinations of kernel size and memory size. This patch makes sure that head.S also maps enough space to fit the kernel pagetables as well as the kernel itself. It ends up using an additional two pages of unreclaimable memory. Signed-off-by: Jeremy Fitzhardinge <[EMAIL PROTECTED]> Cc: Andi Kleen <[EMAIL PROTECTED]> Cc: Zachary Amsden <[EMAIL PROTECTED]> Cc: Chris Wright <[EMAIL PROTECTED]> Cc: "Eric W. Biederman" <[EMAIL PROTECTED]> Cc: "H. Peter Anvin" <[EMAIL PROTECTED]> Cc: Linus Torvalds <[EMAIL PROTECTED]>, --- arch/i386/kernel/head.S | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) =================================================================== --- a/arch/i386/kernel/head.S +++ b/arch/i386/kernel/head.S @@ -34,16 +34,19 @@ /* * This is how much memory *in addition to the memory covered up to - * and including _end* we need mapped initially. We need one bit for - * each possible page, but only in low memory, which means - * 2^32/4096/8 = 128K worst case (4G/4G split.) + * and including _end* we need mapped initially. + * We need: + * - one bit for each possible page, but only in low memory, which means + * 2^32/4096/8 = 128K worst case (4G/4G split.) + * - enough space to map all low memory, which means + * (2^32/4096) / 512 + 4 pages (worst case for PAE) * * Modulo rounding, each megabyte assigned here requires a kilobyte of * memory, which is currently unreclaimed. * * This should be a multiple of a page. */ -#define INIT_MAP_BEYOND_END (128*1024) +#define INIT_MAP_BEYOND_END (128*1024 + (2048 + 4)*4096) /* - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/