svn commit: r223307 - head/sys/vm
Warner Losh
imp at bsdimp.com
Tue Jun 21 22:19:36 UTC 2011
On Jun 21, 2011, at 2:30 PM, 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_clear_8???? I only see atomic_clear_int, which should be atomic_clear_4 in the mips impl.
Warner
> Thanks a lot!
> /bz
>
>
>> Reviewed by: attilio, kib
>>
>> Modified:
>> head/sys/vm/vm_fault.c
>> head/sys/vm/vm_page.c
>> head/sys/vm/vm_page.h
>>
>> Modified: head/sys/vm/vm_fault.c
>> ==============================================================================
>> --- head/sys/vm/vm_fault.c Sun Jun 19 18:34:49 2011 (r223306)
>> +++ head/sys/vm/vm_fault.c Sun Jun 19 19:13:24 2011 (r223307)
>> @@ -1089,10 +1089,20 @@ vm_fault_quick_hold_pages(vm_map_t map,
>> * caller's changes may go unnoticed because they are
>> * performed through an unmanaged mapping or by a DMA
>> * operation.
>> + *
>> + * The object lock is not held here. Therefore, like
>> + * a pmap operation, the page queues lock may be
>> + * required in order to call vm_page_dirty(). See
>> + * vm_page_clear_dirty_mask().
>> */
>> +#if defined(__amd64__) || defined(__i386__) || defined(__ia64__) || \
>> + defined(__mips__)
>> + vm_page_dirty(*mp);
>> +#else
>> vm_page_lock_queues();
>> vm_page_dirty(*mp);
>> vm_page_unlock_queues();
>> +#endif
>> }
>> }
>> if (pmap_failed) {
>>
>> Modified: head/sys/vm/vm_page.c
>> ==============================================================================
>> --- head/sys/vm/vm_page.c Sun Jun 19 18:34:49 2011 (r223306)
>> +++ head/sys/vm/vm_page.c Sun Jun 19 19:13:24 2011 (r223307)
>> @@ -729,7 +729,12 @@ vm_page_sleep(vm_page_t m, const char *m
>> /*
>> * vm_page_dirty:
>> *
>> - * make page all dirty
>> + * Set all bits in the page's dirty field.
>> + *
>> + * The object containing the specified page must be locked if the call is
>> + * made from the machine-independent layer. If, however, the call is
>> + * made from the pmap layer, then the page queues lock may be required.
>> + * See vm_page_clear_dirty_mask().
>> */
>> void
>> vm_page_dirty(vm_page_t m)
>> @@ -2325,15 +2330,41 @@ vm_page_clear_dirty_mask(vm_page_t m, in
>> /*
>> * If the object is locked and the page is neither VPO_BUSY nor
>> * PG_WRITEABLE, then the page's dirty field cannot possibly be
>> - * modified by a concurrent pmap operation.
>> + * set by a concurrent pmap operation.
>> */
>> VM_OBJECT_LOCK_ASSERT(m->object, MA_OWNED);
>> if ((m->oflags & VPO_BUSY) == 0 && (m->flags & PG_WRITEABLE) == 0)
>> m->dirty &= ~pagebits;
>> else {
>> +#if defined(__amd64__) || defined(__i386__) || defined(__ia64__) || \
>> + defined(__mips__)
>> + /*
>> + * On the aforementioned architectures, the page queues lock
>> + * is not required by the following read-modify-write
>> + * operation. The combination of the object's lock and an
>> + * atomic operation suffice. Moreover, the pmap layer on
>> + * these architectures can call vm_page_dirty() without
>> + * holding the page queues lock.
>> + */
>> +#if PAGE_SIZE == 4096
>> + atomic_clear_char(&m->dirty, pagebits);
>> +#elif PAGE_SIZE == 8192
>> + atomic_clear_short(&m->dirty, pagebits);
>> +#elif PAGE_SIZE == 16384
>> + atomic_clear_int(&m->dirty, pagebits);
>> +#else
>> +#error "PAGE_SIZE is not supported."
>> +#endif
>> +#else
>> + /*
>> + * Otherwise, the page queues lock is required to ensure that
>> + * a concurrent pmap operation does not set the page's dirty
>> + * field during the following read-modify-write operation.
>> + */
>> vm_page_lock_queues();
>> m->dirty &= ~pagebits;
>> vm_page_unlock_queues();
>> +#endif
>> }
>> }
>>
>>
>> Modified: head/sys/vm/vm_page.h
>> ==============================================================================
>> --- head/sys/vm/vm_page.h Sun Jun 19 18:34:49 2011 (r223306)
>> +++ head/sys/vm/vm_page.h Sun Jun 19 19:13:24 2011 (r223307)
>> @@ -89,10 +89,26 @@
>> * and offset to which this page belongs (for pageout),
>> * and sundry status bits.
>> *
>> - * Fields in this structure are locked either by the lock on the
>> - * object that the page belongs to (O), its corresponding page lock (P),
>> - * or by the lock on the page queues (Q).
>> - *
>> + * In general, operations on this structure's mutable fields are
>> + * synchronized using either one of or a combination of the lock on the
>> + * object that the page belongs to (O), the pool lock for the page (P),
>> + * or the lock for either the free or paging queues (Q). If a field is
>> + * annotated below with two of these locks, then holding either lock is
>> + * sufficient for read access, but both locks are required for write
>> + * access.
>> + *
>> + * In contrast, the synchronization of accesses to the page's dirty field
>> + * is machine dependent (M). In the machine-independent layer, the lock
>> + * on the object that the page belongs to must be held in order to
>> + * operate on the field. However, the pmap layer is permitted to set
>> + * all bits within the field without holding that lock. Therefore, if
>> + * the underlying architecture does not support atomic read-modify-write
>> + * operations on the field's type, then the machine-independent layer
>> + * must also hold the page queues lock when performing read-modify-write
>> + * operations and the pmap layer must hold the page queues lock when
>> + * setting the field. In the machine-independent layer, the
>> + * implementation of read-modify-write operations on the field is
>> + * encapsulated in vm_page_clear_dirty_mask().
>> */
>>
>> TAILQ_HEAD(pglist, vm_page);
>> @@ -120,18 +136,19 @@ struct vm_page {
>> u_char busy; /* page busy count (O) */
>> /* NOTE that these must support one bit per DEV_BSIZE in a page!!! */
>> /* so, on normal X86 kernels, they must be at least 8 bits wide */
>> + /* In reality, support for 32KB pages is not fully implemented. */
>> #if PAGE_SIZE == 4096
>> u_char valid; /* map of valid DEV_BSIZE chunks (O) */
>> - u_char dirty; /* map of dirty DEV_BSIZE chunks (O) */
>> + u_char dirty; /* map of dirty DEV_BSIZE chunks (M) */
>> #elif PAGE_SIZE == 8192
>> u_short valid; /* map of valid DEV_BSIZE chunks (O) */
>> - u_short dirty; /* map of dirty DEV_BSIZE chunks (O) */
>> + u_short dirty; /* map of dirty DEV_BSIZE chunks (M) */
>> #elif PAGE_SIZE == 16384
>> u_int valid; /* map of valid DEV_BSIZE chunks (O) */
>> - u_int dirty; /* map of dirty DEV_BSIZE chunks (O) */
>> + u_int dirty; /* map of dirty DEV_BSIZE chunks (M) */
>> #elif PAGE_SIZE == 32768
>> u_long valid; /* map of valid DEV_BSIZE chunks (O) */
>> - u_long dirty; /* map of dirty DEV_BSIZE chunks (O) */
>> + u_long dirty; /* map of dirty DEV_BSIZE chunks (M) */
>> #endif
>> };
>>
>
> --
> Bjoern A. Zeeb You have to have visions!
> Stop bit received. Insert coin for new address family.
>
>
>
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