Date: Mon, 7 Nov 2011 14:03:57 -0500 From: Arnaud Lacombe <lacombar@gmail.com> To: Attilio Rao <attilio@freebsd.org> Cc: "K. Macy" <kmacy@freebsd.org>, Alan Cox <alc@rice.edu>, Andriy Gapon <avg@freebsd.org>, freebsd-current@freebsd.org, Benjamin Kaduk <kaduk@mit.edu>, Kostik Belousov <kostikbel@gmail.com>, Penta Upa <bsdboot@gmail.com> Subject: Re: vm_page_t related KBI [Was: Re: panic at vm_page_wire with FreeBSD 9.0 Beta 3] Message-ID: <CACqU3MXJdh9T14vGHi_xENtLMJ8i=nQRNZ_5CVL_jyaPJS_wog@mail.gmail.com> In-Reply-To: <CAJ-FndAOmLHHybUPThjjp14zwe4re%2BL481iv4=8_TE6o2CNYyQ@mail.gmail.com> References: <alpine.GSO.1.10.1111020203230.882@multics.mit.edu> <4EB11C32.80106@FreeBSD.org> <4EB22938.4050803@rice.edu> <20111103132437.GV50300@deviant.kiev.zoral.com.ua> <4EB2D48E.1030102@rice.edu> <20111104100828.GG50300@deviant.kiev.zoral.com.ua> <4EB40015.5040100@rice.edu> <20111104153004.GK50300@deviant.kiev.zoral.com.ua> <4EB4095D.3030303@rice.edu> <20111104160339.GM50300@deviant.kiev.zoral.com.ua> <20111105141306.GW50300@deviant.kiev.zoral.com.ua> <CACqU3MXH%2ByBnBPNA_FD2G_KPLifzc2h7a5=ErnO=xu_FEmg4TQ@mail.gmail.com> <CAJ-FndAOmLHHybUPThjjp14zwe4re%2BL481iv4=8_TE6o2CNYyQ@mail.gmail.com>
next in thread | previous in thread | raw e-mail | index | archive | help
On Mon, Nov 7, 2011 at 4:36 AM, Attilio Rao <attilio@freebsd.org> wrote:
> 2011/11/7 Arnaud Lacombe <lacombar@gmail.com>:
>> Hi,
>>
>> On Sat, Nov 5, 2011 at 10:13 AM, Kostik Belousov <kostikbel@gmail.com> w=
rote:
>>> On Fri, Nov 04, 2011 at 06:03:39PM +0200, Kostik Belousov wrote:
>>>
>>> Below is the KBI patch after vm_page_bits_t merge is done.
>>> Again, I did not spent time converting all in-tree consumers
>>> from the (potentially) loadable modules to the new KPI until it
>>> is agreed upon.
>>>
>>> diff --git a/sys/nfsclient/nfs_bio.c b/sys/nfsclient/nfs_bio.c
>>> index 305c189..7264cd1 100644
>>> --- a/sys/nfsclient/nfs_bio.c
>>> +++ b/sys/nfsclient/nfs_bio.c
>>> @@ -128,7 +128,7 @@ nfs_getpages(struct vop_getpages_args *ap)
>>> =A0 =A0 =A0 =A0 * can only occur at the file EOF.
>>> =A0 =A0 =A0 =A0 */
>>> =A0 =A0 =A0 =A0VM_OBJECT_LOCK(object);
>>> - =A0 =A0 =A0 if (pages[ap->a_reqpage]->valid !=3D 0) {
>>> + =A0 =A0 =A0 if (vm_page_read_valid(pages[ap->a_reqpage]) !=3D 0) {
>>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0for (i =3D 0; i < npages; ++i) {
>>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0if (i !=3D ap->a_reqpage=
) {
>>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0vm_page_=
lock(pages[i]);
>>> @@ -198,16 +198,16 @@ nfs_getpages(struct vop_getpages_args *ap)
>>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0/*
>>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 * Read operation filled=
an entire page
>>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 */
>>> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 m->valid =3D VM_PAGE_BITS=
_ALL;
>>> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 KASSERT(m->dirty =3D=3D 0=
,
>>> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 vm_page_write_valid(m, VM=
_PAGE_BITS_ALL);
>>> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 KASSERT(vm_page_read_dirt=
y(m) =3D=3D 0,
>>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0("nfs_getpages: =
page %p is dirty", m));
>>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0} else if (size > toff) {
>>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0/*
>>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 * Read operation filled=
a partial page.
>>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 */
>>> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 m->valid =3D 0;
>>> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 vm_page_write_valid(m, 0)=
;
>>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0vm_page_set_valid(m, 0, =
size - toff);
>>> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 KASSERT(m->dirty =3D=3D 0=
,
>>> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 KASSERT(vm_page_read_dirt=
y(m) =3D=3D 0,
>>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0("nfs_getpages: =
page %p is dirty", m));
>>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0} else {
>>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0/*
>>> diff --git a/sys/vm/vm_page.c b/sys/vm/vm_page.c
>>> index 389aea5..2f41e70 100644
>>> --- a/sys/vm/vm_page.c
>>> +++ b/sys/vm/vm_page.c
>>> @@ -2677,6 +2677,66 @@ vm_page_test_dirty(vm_page_t m)
>>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0vm_page_dirty(m);
>>> =A0}
>>>
>>> +void
>>> +vm_page_lock_func(vm_page_t m, const char *file, int line)
>>> +{
>>> +
>>> +#if LOCK_DEBUG > 0 || defined(MUTEX_NOINLINE)
>>> + =A0 =A0 =A0 _mtx_lock_flags(vm_page_lockptr(m), 0, file, line);
>>> +#else
>>> + =A0 =A0 =A0 __mtx_lock(vm_page_lockptr(m), 0, file, line);
>>> +#endif
>>> +}
>>> +
>> Why do you re-implement the wheel ? all the point of these assessors
>> is to hide implementation detail. IMO, you should restrict yourself to
>> the documented API from mutex(9), only.
>>
>> Oh, wait, you end-up using LOCK_FILE instead of just __FILE__, but
>> wait LOCK_FILE is either just __FILE__, or NULL, depending on
>> LOCK_DEBUG, but you wouldn't have those function without
>> INVARIANTS.... This whole LOCK_FILE/LOCK_LINE seem completely
>> fracked-up... If you don't want this code in INVARIANTS, but in
>> LOCK_DEBUG, only make it live only in the LOCK_DEBUG case.
>>
>> Btw, let me also question the use of non-inline functions.
>
> My impression is that you don't really understand the patch, thus your
> disrespectful words used here are really unjustified.
>
Well, unfortunately, I wasn't around to comment 10 years ago when this got =
in.
> I think that kib@ intention is just to get "the most official way" to
> pass down file and line to locking functions from the consumers.
> His patch is "technically right", but I would prefer something
> different (see below).
>
Yes, and that's not an excuse to use the _internal_ implementation
details of mutex(9), and not the exposed API. This is especially true
when applied to someone so eager to follow "standards".
> LOCK_FILE and LOCK_LINE exist for reducing the space in .rodata
> section. Without INVARIANTS/WITNESS/etc. they will just be NULL and
> not pointing to a lot of datas that won't be used in the opposite
> case.
>
You comment just as if __FILE__ and __LINE__ were mandatory in a debug
interface. This is _not_ true. __FILE__ and __LINE__ are just hideous
for debugging of anything but early alpha code. LOCK_FILE and
LOCK_LINE are a bad answer to a bad interface. Even if you just pass
NULL and 0 as argument, you've got the bloat of passing unused
argument. You might as well just pass a single argument that would do
the exact same job and be _always_ available, eg. the IP of the
caller, or the first return address. KDB magic still let you translate
to something humanly understandable. If the toolchain does not support
the feature on all supported platform, well, fix the toolchain.
> I'm unsure if this replies to your concerns because you just criticize
> without making a real technical question in this post.
>
I made comments on 3 points:
- using internal implementation details of mutex(9) is broken
- LOCK_FILE/LOCK_LINE are broken (a bit of a divergence on the
original subject :/)
- there is _no_ reason not to use inlines function for such trivial onelin=
ers
so obviously, we did not read the same comments.
- Arnaud
>>> +void
>>> +vm_page_unlock_func(vm_page_t m, const char *file, int line)
>>> +{
>>> +
>>> +#if LOCK_DEBUG > 0 || defined(MUTEX_NOINLINE)
>>> + =A0 =A0 =A0 _mtx_unlock_flags(vm_page_lockptr(m), 0, file, line);
>>> +#else
>>> + =A0 =A0 =A0 __mtx_unlock(vm_page_lockptr(m), curthread, 0, file, line=
);
>>> +#endif
>>> +}
>
> Kostik,
> we usually catered this case by having interfaces directly specified
> in mutex.h in order to keep the implementation details "compact
> enough" (see the thread_lock() case for this).
>
> I'm unsure what you prefer here, at least for the locking functions
> you could move over there as there are cons and prons for both
> approaches really and I'm fine with both.
>
> Attilio
>
>
> --
> Peace can only be achieved by understanding - A. Einstein
>
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?CACqU3MXJdh9T14vGHi_xENtLMJ8i=nQRNZ_5CVL_jyaPJS_wog>