svn commit: r223307 - head/sys/vm

[John Baldwin]

On Tuesday, June 21, 2011 4:58:10 pm Bruce Evans wrote:
> On Tue, 21 Jun 2011, Bjoern A. Zeeb wrote:
> 
> > On Jun 19, 2011, at 7:13 PM, Alan Cox wrote:
> >
> > Hi Alan,
> >
> >> Author: alc
> >> Date: Sun Jun 19 19:13:24 2011
> >> New Revision: 223307
> >> URL: http://svn.freebsd.org/changeset/base/223307
> >>
> >> Log:
> >>  Precisely document the synchronization rules for the page's dirty field.
> >>  (Saying that the lock on the object that the page belongs to must be held
> >>  only represents one aspect of the rules.)
> >>
> >>  Eliminate the use of the page queues lock for atomically performing read-
> >>  modify-write operations on the dirty field when the underlying architecture
> >>  supports atomic operations on char and short types.
> >>
> >>  Document the fact that 32KB pages aren't really supported.
> >
> > contrary to the tinderbox I'd like to point out that all mips kernels built by universe are broken with a SVN HEAD from earlier today.  Could 
you please check and see if you can fix it?  The errors I get are:
> >
> > vm_page.o: In function `vm_page_clear_dirty':
> > /sys/vm/vm_page.c:(.text+0x18d0): undefined reference to `atomic_clear_8'
> > /sys/vm/vm_page.c:(.text+0x18d0): relocation truncated to fit: R_MIPS_26 against `atomic_clear_8'
> > vm_page.o: In function `vm_page_set_validclean':
> > /sys/vm/vm_page.c:(.text+0x38f0): undefined reference to `atomic_clear_8'
> > /sys/vm/vm_page.c:(.text+0x38f0): relocation truncated to fit: R_MIPS_26 against `atomic_clear_8'
> 
> Atomic types shorter than int cannot be used in MI code, since they might
> not exist.  Apparently they don't exist on mips.  jake@ fixed all their
> old uses for sparc4 in ~Y2K.

I agree.  Is there any harm in having the 'dirty' and 'valid' fields in
vm_page always be at least of size 'int'?

In the case of amd64, vm_page would change from a size of 120 bytes to 128.

On i386 I think you'd end up changing the size from 68 to 76.

(Using an int results in alignment padding after 'busy'.)

Hmm, that's around 120k of extra vm_page_t space for a machine with 64M of
RAM, so around 0.18% of RAM would be used on both platforms (presumably the
usage would be similar on other platforms as well).  At 24 GB of RAM, the
extra space is just under 0.20% of RAM (48M).

-- 
John Baldwin