Re: [aarcange@redhat.com: [PATCH] fork vs gup(-fast) fix]

[Ingo Molnar <mingo@elte.hu>]

* KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:

> > following patch is my v2 approach.
> > it survive Andrea's three dio test-case.
> >
> > [...]

> Frankly, linus sugessted to insert one branch into do_wp_page(), 
> but I remove one branch from gup_fast.
> 
> I think it's good performance trade-off. but if anybody hate my 
> approach, I'll drop my chicken heart and try to linus suggested 
> way.

We started out with a difficult corner case problem (for an arguably 
botched syscall promise we made to user-space many moons ago), and 
an invasive and unmaintainable looking patch:

    8 files changed, 342 insertions(+), 77 deletions(-)

And your v2 is now:

    9 files changed, 66 insertions(+), 21 deletions(-)

... and it is also speeding up fast-gup. Which is a marked 
improvement IMO.

	Ingo

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