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

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Date:	Sun, 25 Feb 2007 04:06:57 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Nick Piggin <npiggin@...e.de>
Cc:	linux-kernel@...r.kernel.org, npiggin@...e.de, linux-mm@...ck.org
Subject: Re: [patch 3/3] mm: fix PageUptodate memorder

What an unpleasing patchset.  I really really hope we really have a bug in
there, and that all this crap isn't pointless uglification.

We _do_ need a flush_dcaceh_page() in all cases which you're concerned
about.  Perhaps we should stick the appropriate barriers in there.

> On Thu, 15 Feb 2007 08:31:31 +0100 (CET) Nick Piggin <npiggin@...e.de> wrote:
> +static inline void SetNewPageUptodate(struct page *page)
> +{
> +	/*
> +	 * S390 sets page dirty bit on IO operations, which is why it is
> +	 * cleared in SetPageUptodate. This is not an issue for newly
> +	 * allocated pages that are brought uptodate by zeroing memory.
> +	 */
> +	smp_wmb();
> +	__set_bit(PG_uptodate, &(page)->flags);
> +}

__SetPageUptodate() might be more conventional.

Boy we'd better get the callers of this little handgrenade right.
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