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SubjectRe: [PATCH 05 of 66] compound_lock
On Wed, Nov 03, 2010 at 04:27:40PM +0100, Andrea Arcangeli wrote:
> From: Andrea Arcangeli <aarcange@redhat.com>
>
> Add a new compound_lock() needed to serialize put_page against
> __split_huge_page_refcount().
>

Does it only apply to a compound page? If I pass in a PageTail, what
happens? Could do with a beefier description on why it's needed but
maybe it's obvious later.

> Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
> Acked-by: Rik van Riel <riel@redhat.com>
> ---
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -14,6 +14,7 @@
> #include <linux/mm_types.h>
> #include <linux/range.h>
> #include <linux/pfn.h>
> +#include <linux/bit_spinlock.h>
>
> struct mempolicy;
> struct anon_vma;
> @@ -302,6 +303,40 @@ static inline int is_vmalloc_or_module_a
> }
> #endif
>
> +static inline void compound_lock(struct page *page)
> +{
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> + bit_spin_lock(PG_compound_lock, &page->flags);
> +#endif
> +}
> +
> +static inline void compound_unlock(struct page *page)
> +{
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> + bit_spin_unlock(PG_compound_lock, &page->flags);
> +#endif
> +}
> +
> +static inline void compound_lock_irqsave(struct page *page,
> + unsigned long *flagsp)
> +{
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> + unsigned long flags;
> + local_irq_save(flags);
> + compound_lock(page);
> + *flagsp = flags;
> +#endif
> +}
> +

The pattern for spinlock irqsave passes in unsigned long, not unsigned
long *. It'd be nice if they matched.

> +static inline void compound_unlock_irqrestore(struct page *page,
> + unsigned long flags)
> +{
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> + compound_unlock(page);
> + local_irq_restore(flags);
> +#endif
> +}
> +
> static inline struct page *compound_head(struct page *page)
> {
> if (unlikely(PageTail(page)))
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -108,6 +108,9 @@ enum pageflags {
> #ifdef CONFIG_MEMORY_FAILURE
> PG_hwpoison, /* hardware poisoned page. Don't touch */
> #endif
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> + PG_compound_lock,
> +#endif
> __NR_PAGEFLAGS,
>
> /* Filesystems */
> @@ -397,6 +400,12 @@ static inline void __ClearPageTail(struc
> #define __PG_MLOCKED 0
> #endif
>
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +#define __PG_COMPOUND_LOCK (1 << PG_compound_lock)
> +#else
> +#define __PG_COMPOUND_LOCK 0
> +#endif
> +
> /*
> * Flags checked when a page is freed. Pages being freed should not have
> * these flags set. It they are, there is a problem.
> @@ -406,7 +415,8 @@ static inline void __ClearPageTail(struc
> 1 << PG_private | 1 << PG_private_2 | \
> 1 << PG_buddy | 1 << PG_writeback | 1 << PG_reserved | \
> 1 << PG_slab | 1 << PG_swapcache | 1 << PG_active | \
> - 1 << PG_unevictable | __PG_MLOCKED | __PG_HWPOISON)
> + 1 << PG_unevictable | __PG_MLOCKED | __PG_HWPOISON | \
> + __PG_COMPOUND_LOCK)
>
> /*
> * Flags checked when a page is prepped for return by the page allocator.
>

--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab


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