On Tue, Aug 09, 2005 at 07:29:30PM +1000, Nick Piggin wrote: > Russell King wrote: > > The usage of "valid ram" here is confusing - that's not what PageReserved > > is all about. It's about valid RAM which is managed by method other > > than the usual page counting. Non-reserved RAM is also valid RAM, but > > is managed by the kernel in the usual way. > > Well that is one usage of the PageReserved flag. That one tends > to be easily covered by VM_RESERVED (ie. it is no longer used that > way after the patches). > > The remaining problem is, in fact, these "other" uses of PageReserved. > One usage definitely appears to be "is this page valid RAM?".
Hmm, that sounds like an architecture specific extension above the basic requirements. > > The former is available for remap_pfn_range and ioremap, the latter is > > not. > > I thought ioremap was attempting to avoid remapping physical > RAM with that check. All drivers I have looked at which allocate > physical memory then SetPageReserved the pages use remap_pfn_range > but I admit that's not a huge number (that I have looked at). They do this because: 1. they want to control when this RAM is freed. 2. remap_pfn_range refuses to map RAM that isn't marked reserved. To put it another way, they fiddle with the reserved bit because that's what the current interfaces forces upon them. I would dearly like that to go away though. > > On the other hand, the validity of an apparant RAM address can only be > > tested using its pfn with pfn_valid(). > > I'm fairly sure that's not the case on i386 at least. I think > pfn_valid will be true if the pfn points to a struct page. > See arch/i386/mm/init.c:one_highpage_init() This sounds like i386 is doing something which is a superset of the base requirements, which is an architecture specific extension. No problem with that, but that's i386 folk's problem. 8) Ok, but I still disagree with replacing something called reserved with something which leads one to believe that it's intended for checking whether a struct page is "valid" RAM or not when there's other interfaces which are supposed to be used for that. I wonder if we can optimise out the useless "valid" RAM checks on architectures which don't require this insanity... -- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of: 2.6 Serial core - 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/
