linux/include/asm-um
Nick Piggin 7e675137a8 mm: introduce pte_special pte bit
s390 for one, cannot implement VM_MIXEDMAP with pfn_valid, due to their memory
model (which is more dynamic than most).  Instead, they had proposed to
implement it with an additional path through vm_normal_page(), using a bit in
the pte to determine whether or not the page should be refcounted:

vm_normal_page()
{
	...
        if (unlikely(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP))) {
                if (vma->vm_flags & VM_MIXEDMAP) {
#ifdef s390
			if (!mixedmap_refcount_pte(pte))
				return NULL;
#else
                        if (!pfn_valid(pfn))
                                return NULL;
#endif
                        goto out;
                }
	...
}

This is fine, however if we are allowed to use a bit in the pte to determine
refcountedness, we can use that to _completely_ replace all the vma based
schemes.  So instead of adding more cases to the already complex vma-based
scheme, we can have a clearly seperate and simple pte-based scheme (and get
slightly better code generation in the process):

vm_normal_page()
{
#ifdef s390
	if (!mixedmap_refcount_pte(pte))
		return NULL;
	return pte_page(pte);
#else
	...
#endif
}

And finally, we may rather make this concept usable by any architecture rather
than making it s390 only, so implement a new type of pte state for this.
Unfortunately the old vma based code must stay, because some architectures may
not be able to spare pte bits.  This makes vm_normal_page a little bit more
ugly than we would like, but the 2 cases are clearly seperate.

So introduce a pte_special pte state, and use it in mm/memory.c.  It is
currently a noop for all architectures, so this doesn't actually result in any
compiled code changes to mm/memory.o.

BTW:
I haven't put vm_normal_page() into arch code as-per an earlier suggestion.
The reason is that, regardless of where vm_normal_page is actually
implemented, the *abstraction* is still exactly the same. Also, while it
depends on whether the architecture has pte_special or not, that is the
only two possible cases, and it really isn't an arch specific function --
the role of the arch code should be to provide primitive functions and
accessors with which to build the core code; pte_special does that. We do
not want architectures to know or care about vm_normal_page itself, and
we definitely don't want them being able to invent something new there
out of sight of mm/ code. If we made vm_normal_page an arch function, then
we have to make vm_insert_mixed (next patch) an arch function too. So I
don't think moving it to arch code fundamentally improves any abstractions,
while it does practically make the code more difficult to follow, for both
mm and arch developers, and easier to misuse.

[akpm@linux-foundation.org: build fix]
Signed-off-by: Nick Piggin <npiggin@suse.de>
Acked-by: Carsten Otte <cotte@de.ibm.com>
Cc: Jared Hulbert <jaredeh@gmail.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-04-28 08:58:23 -07:00
..
a.out-core.h aout: suppress A.OUT library support if !CONFIG_ARCH_SUPPORTS_AOUT 2008-02-08 09:22:30 -08:00
a.out.h aout: move STACK_TOP[_MAX] to asm/processor.h 2008-02-08 09:22:29 -08:00
alternative-asm.h x86: rename .i assembler includes to .h 2007-10-17 20:16:29 +02:00
alternative.h
apic.h
archparam-i386.h
archparam-ppc.h
archparam-x86_64.h
asm.h uml: add asm-um/asm.h 2008-01-30 13:31:17 +01:00
atomic.h
auxvec.h
bitops.h forbid asm/bitops.h direct inclusion 2007-10-19 11:53:41 -07:00
boot.h
bug.h
bugs.h
byteorder.h
cache.h
cacheflush.h
calling.h
checksum.h
cmpxchg.h
cobalt.h
common.lds.S
cpufeature.h
cputime.h
current.h uml: current.h cleanup 2008-02-05 09:44:28 -08:00
delay.h
desc.h
device.h
div64.h
dma-mapping.h
dma.h
dwarf2.h
elf-i386.h uml: style cleanup 2008-02-05 09:44:28 -08:00
elf-ppc.h
elf-x86_64.h uml: header untangling 2008-02-05 09:44:28 -08:00
emergency-restart.h
errno.h
fcntl.h
fixmap.h uml: runtime host VMSPLIT detection 2008-02-08 09:22:42 -08:00
floppy.h
frame.h x86: rename .i assembler includes to .h 2007-10-17 20:16:29 +02:00
futex.h
hardirq.h
highmem.h
host_ldt-i386.h
host_ldt-x86_64.h
hw_irq.h
ide.h
io.h
ioctl.h
ioctls.h
ipcbuf.h
irq_regs.h
irq_vectors.h
irq.h
irqflags.h
kdebug.h
keyboard.h
kmap_types.h
kvm.h kvm: provide kvm.h for all architecture: fixes headers_install 2008-04-02 15:28:18 -07:00
ldt.h uml: LDT mutex conversion 2008-02-05 09:44:31 -08:00
linkage.h uml: get rid of asmlinkage 2008-02-05 09:44:25 -08:00
local.h
locks.h
mca_dma.h
mman.h
mmu_context.h uml: cover stubs with a VMA 2008-02-05 09:44:29 -08:00
mmu.h
module-generic.h
module-i386.h
module-x86_64.h
msgbuf.h
mtrr.h
mutex.h
namei.h
nops.h git-x86: unbreak UML 2008-01-30 13:32:38 +01:00
page_offset.h
page.h CONFIG_HIGHPTE vs. sub-page page tables. 2008-02-08 09:22:42 -08:00
param.h uml: add back CONFIG_HZ 2008-02-05 09:44:31 -08:00
paravirt.h
pci.h
pda.h
percpu.h
pgalloc.h CONFIG_HIGHPTE vs. sub-page page tables. 2008-02-08 09:22:42 -08:00
pgtable-2level.h uml: 64-bit tlb fixes 2008-02-05 09:44:29 -08:00
pgtable-3level.h uml: 64-bit tlb fixes 2008-02-05 09:44:29 -08:00
pgtable.h mm: introduce pte_special pte bit 2008-04-28 08:58:23 -07:00
poll.h
posix_types.h
prctl.h
processor-generic.h uml: runtime host VMSPLIT detection 2008-02-08 09:22:42 -08:00
processor-i386.h uml: remove xmm checking on x86 2008-02-05 09:44:24 -08:00
processor-ppc.h
processor-x86_64.h uml: x86_64 should copy %fs during fork 2008-02-08 09:22:43 -08:00
ptrace-generic.h uml: ptrace floating point fixes 2007-10-16 09:43:07 -07:00
ptrace-i386.h uml: ptrace floating point fixes 2007-10-16 09:43:07 -07:00
ptrace-x86_64.h uml: remove code made redundant by CHOOSE_MODE removal 2007-10-16 09:43:05 -07:00
required-features.h
resource.h
rwlock.h
rwsem.h
scatterlist.h
sections.h
segment.h
semaphore.h Generic semaphore implementation 2008-04-17 10:42:34 -04:00
sembuf.h
serial.h
setup.h
shmbuf.h
shmparam.h
sigcontext-generic.h
sigcontext-i386.h
sigcontext-ppc.h
sigcontext-x86_64.h
siginfo.h
signal.h
smp.h uml: fix inlines 2007-10-16 09:43:06 -07:00
socket.h
sockios.h
spinlock_types.h
spinlock.h
stat.h
statfs.h
string.h
suspend.h
system-generic.h
system-i386.h
system-ppc.h
system-x86_64.h
termbits.h
termios.h
thread_info.h uml: current.h cleanup 2008-02-05 09:44:28 -08:00
timex.h
tlb.h uml: compile error fix 2008-04-15 19:35:40 -07:00
tlbflush.h remove unused flush_tlb_pgtables 2007-10-19 11:53:34 -07:00
topology.h
types.h
uaccess.h uml: header untangling 2008-02-05 09:44:28 -08:00
ucontext.h
unaligned.h
unistd.h x86 merge fallout: uml 2007-10-29 07:41:32 -07:00
user.h
vga.h
vm86.h
vm-flags-i386.h
vm-flags-x86_64.h
xor.h