Messages in this thread | ![/](/images/icornerl.gif) | | Date | Tue, 29 Jun 2004 11:58:30 +0100 | From | Russell King <> | Subject | Re: [BUG FIX] [PATCH] fork_init() max_low_pfn fixes potential OOM bug on big highmem machine |
| |
On Tue, Jun 29, 2004 at 06:48:14PM +0800, Coywolf Qi Hunt wrote: > Russell King wrote: > Actually there's physical DRAM offset: PHY_OFFSET, defined on ARM only. > max_low_pfn happens to be the same as `num_lowpages'. > These assignments seems illogical in naming. But just happen to let this > patch work. Other platforms may still break.
That may be a bug actually. Looking at ll_rw_blk.c:
unsigned long bounce_pfn = dma_addr >> PAGE_SHIFT; if (bounce_pfn < blk_max_low_pfn) {
blk_max_low_pfn = max_low_pfn;
dma_addr are physical addresses, so bounce_pfn is referenced to a PFN0 equal to physical address 0. This implies that blk_max_low_pfn is likewise, as is max_low_pfn.
> [coywolf@everest ~/linux-2.6.7/arch]$ grep max_low_pfn arm* -rn > arm/mm/init.c:235: max_low_pfn = memend_pfn - O_PFN_DOWN(PHYS_OFFSET);
However, here, max_low_pfn of zero corresponds with the PFN of PHYS_OFFSET. We have something with two different origins being compared, which is nonsense. So something is wrong somewhere, and my money is on max_low_pfn.
-- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of: 2.6 PCMCIA - http://pcmcia.arm.linux.org.uk/ 2.6 Serial core - 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/
| ![\](/images/icornerr.gif) |