Jeremy Fitzhardinge <[EMAIL PROTECTED]> writes: > Eric W. Biederman wrote: >> Jeremy did your kernel have PAE enabled? >> >> It just occurred to me that we have at all of the memory below 1M (say about >> 512K) mapped and available to setup new mappings. >> >> The only way I can see a page fault happening is if you were using a PAE >> enabled kernel (so you were not updating the current page tables) and >> you have more than 256M of low memory, and we don't get any much extra >> from always mapping 4M at a time. > > Yes, that's the situation. PAE enabled, ~768MB of memory and a large > kernel which mostly fills the 8M mapping.
And it just occurred to me PSE disabled, otherwise you would not have needed more than 4 pages. I supposed you were testing the Xen case. That said I know for certain now why we have never seen this in production because all cpus that fit this configuration also support PSE. So the way I think we should properly fix this is: - Enable PAE early so we are updating our current page table. - Pass a limit to the bootmem allocator so we do not get pages pass the point where we have setup page tables. - Handle memory allocation failures. However only the first part is necessary to solve the problem, in practice even if you are using 4K pages. Eric - 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/
