Nick Piggin <[email protected]> wrote:
>
> Andrew Morton wrote:
>
> >
> > 2.4:
> >
> > MS_ASYNC: dirty the pagecache pages, start I/O
> > MS_SYNC: dirty the pagecache pages, start I/O, wait on I/O
> >
> > 2.6:
> >
> > MS_ASYNC: dirty the pagecache pages
> > MS_SYNC: dirty the pagecache pages, start I/O, wait on I/O.
> >
> > So you're saying that doing the I/O in that 25-100msec window allowed your
> > app to do more pipelining.
> >
> > I think for most scenarios, what we have in 2.6 is better: it gives the app
> > more control over when the I/O should be started.
>
> How so?
>
Well, for example you might want to msync a number of disjoint parts of the
mapping, then write them all out in one hit.
Or you may not actually _want_ to start the I/O now - you just want pdflush
to write things back in a reasonable time period, so you don't have unsynced
data floating about in memory for eight hours. That's a quite reasonable
application of msync(MS_ASYNC).
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