Re: vm_page_t related KBI [Was: Re: panic at vm_page_wire with FreeBSD 9.0 Beta 3]

2011/11/7 Arnaud Lacombe <lacombar_at_gmail.com>:
> Hi,
>
> On Sat, Nov 5, 2011 at 10:13 AM, Kostik Belousov <kostikbel_at_gmail.com> wrote:
>> 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
>> _at__at_ -128,7 +128,7 _at__at_ nfs_getpages(struct vop_getpages_args *ap)
>>         * can only occur at the file EOF.
>>         */
>>        VM_OBJECT_LOCK(object);
>> -       if (pages[ap->a_reqpage]->valid != 0) {
>> +       if (vm_page_read_valid(pages[ap->a_reqpage]) != 0) {
>>                for (i = 0; i < npages; ++i) {
>>                        if (i != ap->a_reqpage) {
>>                                vm_page_lock(pages[i]);
>> _at__at_ -198,16 +198,16 _at__at_ nfs_getpages(struct vop_getpages_args *ap)
>>                        /*
>>                         * Read operation filled an entire page
>>                         */
>> -                       m->valid = VM_PAGE_BITS_ALL;
>> -                       KASSERT(m->dirty == 0,
>> +                       vm_page_write_valid(m, VM_PAGE_BITS_ALL);
>> +                       KASSERT(vm_page_read_dirty(m) == 0,
>>                            ("nfs_getpages: page %p is dirty", m));
>>                } else if (size > toff) {
>>                        /*
>>                         * Read operation filled a partial page.
>>                         */
>> -                       m->valid = 0;
>> +                       vm_page_write_valid(m, 0);
>>                        vm_page_set_valid(m, 0, size - toff);
>> -                       KASSERT(m->dirty == 0,
>> +                       KASSERT(vm_page_read_dirty(m) == 0,
>>                            ("nfs_getpages: page %p is dirty", m));
>>                } else {
>>                        /*
>> 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
>> _at__at_ -2677,6 +2677,66 _at__at_ vm_page_test_dirty(vm_page_t m)
>>                vm_page_dirty(m);
>>  }
>>
>> +void
>> +vm_page_lock_func(vm_page_t m, const char *file, int line)
>> +{
>> +
>> +#if LOCK_DEBUG > 0 || defined(MUTEX_NOINLINE)
>> +       _mtx_lock_flags(vm_page_lockptr(m), 0, file, line);
>> +#else
>> +       __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.

I think that kib_at_ 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).

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.
I'm unsure if this replies to your concerns because you just criticize
without making a real technical question in this post.

>> +void
>> +vm_page_unlock_func(vm_page_t m, const char *file, int line)
>> +{
>> +
>> +#if LOCK_DEBUG > 0 || defined(MUTEX_NOINLINE)
>> +       _mtx_unlock_flags(vm_page_lockptr(m), 0, file, line);
>> +#else
>> +       __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