Re: msync() behaviour broken for MS_ASYNC, revert patch?

[Stephen C. Tweedie]

Hi,

On Fri, 2004-04-16 at 23:35, Jamie Lokier wrote:
> Stephen C. Tweedie wrote:
> > I've been looking at a discrepancy between msync() behaviour on 2.4.9
> > and newer 2.4 kernels, and it looks like things changed again in
> > 2.5.68.
> 
> When you say a discrepancy between 2.4.9 and newer 2.4 kernels, do you
> mean that the msync() behaviour changed during the 2.4 series?

Yes.

> If so, what was the change?

2.4.9 behaved like current 2.6 --- on MS_ASYNC, it did a
set_page_dirty() which means the page will get picked up by the next
5-second bdflush pass.  But later 2.4 kernels were changed so that they
started MS_ASYNC IO immediately with filemap_fdatasync() (which is
asynchronous regarding the new IO, but which blocks synchronously if
there is already old IO in flight on the page.)

That was reverted back to the earlier, 2.4.9 behaviour in the 2.5
series.

Cheers,
 Stephen

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