linux-kernel - Re: [patch 1/3] mm: fix PageUptodate memorder

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Date:	Tue, 6 Feb 2007 00:25:12 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Hugh Dickins <hugh@...itas.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linux Memory Management <linux-mm@...ck.org>,
	Linux Filesystems <linux-fsdevel@...r.kernel.org>
Subject: Re: [patch 1/3] mm: fix PageUptodate memorder

On Tue,  6 Feb 2007 09:02:11 +0100 (CET) Nick Piggin <npiggin@...e.de> wrote:

> +static inline void __SetPageUptodate(struct page *page)
> +{
> +#ifdef CONFIG_S390
>  	if (!test_and_set_bit(PG_uptodate, &page->flags))
>  		page_test_and_clear_dirty(page);
> -}
>  #else
> -#define SetPageUptodate(page)	set_bit(PG_uptodate, &(page)->flags)
> +	/*
> +	 * Memory barrier must be issued before setting the PG_uptodate bit,
> +	 * so all previous writes that served to bring the page uptodate are
> +	 * visible before PageUptodate becomes true.
> +	 *
> +	 * S390 is guaranteed to have a barrier in the test_and_set operation
> +	 * (see Documentation/atomic_ops.txt).
> +	 *
> +	 * XXX: does this memory barrier need to be anything special to
> +	 * handle things like DMA writes into the page?
> +	 */
> +	smp_wmb();
> +	set_bit(PG_uptodate, &(page)->flags);
>  #endif
> +}
> +
> +static inline void SetPageUptodate(struct page *page)
> +{
> +	WARN_ON(!PageLocked(page));
> +	__SetPageUptodate(page);
> +}
> +
> +static inline void SetNewPageUptodate(struct page *page)
> +{
> +	__SetPageUptodate(page);
> +}

I was panicing for a minute when I saw that __SetPageUptodate() in there.

Conventionally the __SetPageFoo namespace is for nonatomic updates to
page->flags.  Can we call this something different?


What a fugly patchset :(
-
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