Re: set_page_dirty vs set_page_dirty_lock

[Michael S. Tsirkin]

Quoting  Nick Piggin <nickpiggin@xxxxxxxxxxxx>:
> > 
> >>or try to do something tricky with page_count to determine
> >>if we need to do a copy in fork() rather than a COW.
> > 
> > 
> > I'm actually reasonably happy with the trick that I'm using:
> > performing a second get_user_pages after DMA and comparing
> > the page lists.
> > However, doing this every time on the off chance that a
> > page was made COW forces me into task context, every time.
> > 
> 
> I think it might be possible to solve it with the early-copy in
> fork(). I'll tinker with it.

A possible way to do this would be adding an option to get_user_pages,
and if selected, setting a flag on all pages in range.
This flag should be cleared in put_page when the reference count drops to 1.

The only thing left would be to do the actual copy if the flag is set.

HTH,

-- 
MST
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