Messages in this thread | | | From | Ian Campbell <> | Date | Mon, 21 Jan 2008 21:23:53 +0000 | Subject | Re: [PATCH] x86: Construct 32 bit boot time page tables in native format. |
| |
On Sun, 2008-01-20 at 20:30 +0200, Mika Penttilä wrote: > > + * 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.) > > + * > > + * 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) > > + > > +/* > > > > You have dropped the requirement to map all of low memory (the boot > allocator is used for instance to construct physical mem mapping). > Either you should fix your INIT_MAP_BEYOND_END or make a big comment > telling us why it isn't necessary anymore to map low mem.
I think you are right. The patch ensures that all the initial page tables themselves have mappings but won't map the additional pages needed for mapping the rest of lowmem.
However, I think it is no longer necessary to map a whole new 4G worth of page table pages because the code in kernel_physical_mapping_init now extends the initial mappings rather than replacing them (see changes to native_pagetable_setup_start). So now we only need to map 4G worth of page tables including the initial page tables. That means we only need to map a fixed set of extra pages rather than the sliding limit currently used in the patch.
I'm not convinced by the additional 16MB for CONFIG_DEBUG_PAGEALLOC -- we map enough pages for page tables for 4G of lowmem -- adding space for an extra 16M seems pointless.
Ian. -- Ian Campbell
Good-bye. I am leaving because I am bored. -- George Saunders' dying words
-- 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/
| |