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Date:      Tue, 21 Jun 2011 20:27:03 -0600
From:      Warner Losh <imp@bsdimp.com>
To:        Alan Cox <alc@rice.edu>
Cc:        src-committers@FreeBSD.org, Alan Cox <alc@FreeBSD.org>, svn-src-all@FreeBSD.org, Attilio Rao <attilio@FreeBSD.org>, "Bjoern A. Zeeb" <bz@FreeBSD.org>, Bruce Evans <brde@optusnet.com.au>, svn-src-head@FreeBSD.org
Subject:   Re: svn commit: r223307 - head/sys/vm
Message-ID:  <BEDB4F71-8151-4799-9272-8CE79CDA6C17@bsdimp.com>
In-Reply-To: <4E0128FF.6020804@rice.edu>
References:  <201106191913.p5JJDOqJ006272@svn.freebsd.org>	<BBC34F79-FFA7-4A05-83B3-DE17E0AB14D0@FreeBSD.org>	<20110622063258.D2275@besplex.bde.org> <BANLkTi=7WnYPQRwE4Hi472DuJz91d1sK=g@mail.gmail.com> <4E0128FF.6020804@rice.edu>

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On Jun 21, 2011, at 5:27 PM, Alan Cox wrote:

> On 06/21/2011 16:09, Attilio Rao wrote:
>> 2011/6/21 Bruce Evans<brde@optusnet.com.au>:
>>> On Tue, 21 Jun 2011, Bjoern A. Zeeb wrote:
>>>=20
>>>> On Jun 19, 2011, at 7:13 PM, Alan Cox wrote:
>>>>=20
>>>> Hi Alan,
>>>>=20
>>>>> Author: alc
>>>>> Date: Sun Jun 19 19:13:24 2011
>>>>> New Revision: 223307
>>>>> URL: http://svn.freebsd.org/changeset/base/223307
>>>>>=20
>>>>> 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.)
>>>>>=20
>>>>>  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.
>>>>>=20
>>>>>  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:
>>>>=20
>>>> 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'm sure they do, they exist in support.S though and may not have the
>> _8 form (they may just have the _char version). I may look at the =
code
>> again to be sure.
>>=20
>=20
> It appears that while mips/include/atomic.h declares the existence of =
atomic_clear_8, mips/mips/support.S doesn't implement it.  In other =
words, only support for int's and short's is currently implemented, not =
char's:
>=20
> # grep atomic_clear mips/mips/support.S
> * atomic_clear_32(u_int32_t *a, u_int32_t b)
> LEAF(atomic_clear_32)
> END(atomic_clear_32)
> * atomic_clear_16(u_int16_t *a, u_int16_t b)
> LEAF(atomic_clear_16)
> END(atomic_clear_16)

The current crop of atomic*16 and atomic*8 functions have the =
restriction that the address must be 32-bit aligned (and it forces this =
by aligning to 32-bits silently and then operates on the low 8 or 16 =
bits in that word!)

I'm guessing that this is likely just wrong.  Comments?

Warner




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