svn commit: r223307 - head/sys/vm
Adrian Chadd
adrian at freebsd.org
Thu Jun 23 02:36:10 UTC 2011
Can this commit please be reverted whilst the kinks are worked out for MIPS?
I'm currently knee deep in MIPS related hackery and I'd rather stay on
an unpatched -HEAD so dogfood can be properly self-consumed.
Thanks,
Adrian
On 20 June 2011 03:13, Alan Cox <alc at freebsd.org> wrote:
> 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.
>
> 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
> };
>
>
More information about the svn-src-head
mailing list