Re: Unnecessary barrier in sync_page()?

[Andrea Arcangeli]

On Wed, Jul 07, 2004 at 11:29:53AM -0700, Andrew Morton wrote:
> Andrea Arcangeli <andrea@xxxxxxx> wrote:
> >
> > however the smp_mb() isn't needed in sync_page, simply because it's
> >  perfectly ok if we start running sync_page before reading pagelocked.
> >  All we care about is to run sync_page _before_ io_schedule() and that we
> >  read PageLocked _after_ prepare_to_wait_exclusive.
> > 
> >  So the locking in between PageLocked and sync_page is _absolutely_
> >  worthless and the smp_mb() can go away.
> 
> IIRC, Chris added that barrier (and several similar) for the reads in
> page_mapping().

how does it help to know the page is not locked before executing
page_mapped?
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