On 04/22/2014 07:48 PM, Linus Torvalds wrote: > On Tue, Apr 22, 2014 at 4:35 PM, H. Peter Anvin <hpa@xxxxxxxxx> wrote: >> I just noticed this: >> >> #define _PAGE_TABLE (_PAGE_PRESENT | _PAGE_RW | _PAGE_USER | \ >> _PAGE_ACCESSED | _PAGE_DIRTY) >> #define _KERNPG_TABLE (_PAGE_PRESENT | _PAGE_RW | _PAGE_ACCESSED | \ >> _PAGE_DIRTY) >> >> Is there a reason we set _PAGE_DIRTY for page tables? It has no >> function, but doesn't do any harm either (the dirty bit is ignored for >> page tables)... it just looks funny to me. > > I think it just got copied, and at least the A bit does matter even in > page tables (well, it gets updated, I don't know how much that > "matters"). So the fact that D is ignored is actually the odd man out. > Yes, not setting the A bit means the hardware will take an assist to set the bit for us, which is a waste of time if we don't care about it. The D bit is the one which made me wonder; I thought either it was just copy & paste, or that it got set to make it more analogous with large pages. -hpa -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>