Re: [PATCH -alternative] mm: hugetlbfs: Close race during teardownof hugetlbfs shared page tables V2 (resend)

From: Mel Gorman
Date: Fri Jul 20 2012 - 10:52:06 EST

On Fri, Jul 20, 2012 at 04:36:35PM +0200, Michal Hocko wrote:
> And here is my attempt for the fix (Hugh mentioned something similar
> earlier but he suggested using special flags in ptes or VMAs). I still
> owe doc. update and it hasn't been tested with too many configs and I
> could missed some definition updates.
> I also think that changelog could be much better, I will add (steal) the
> full bug description if people think that this way is worth going rather
> than the one suggested by Mel.
> To be honest I am not quite happy how I had to pollute generic mm code with
> something that is specific to a single architecture.
> Mel hammered it with the test case and it survived.

Tested-by: Mel Gorman <mgorman@xxxxxxx>

This approach looks more or less like what I was expecting. I like that
the trick was applied to the page table page instead of using PTE tricks
or by bodging it with a VMA flag like I was thinking so kudos for that. I
also prefer this approach to trying to free the page tables on or near

In general I think this patch would execute better than mine because it is
far less heavy-handed but I share your concern that it changes the core MM
quite a bit for a corner case that only one architecture cares about. I am
completely biased of course, but I still prefer my patch because other than
an API change it keeps the bulk of the madness in arch/x86/mm/hugetlbpage.c
. I am also not concerned with the scalability of how quickly we can setup
page table sharing.

Hugh, I'm afraid you get to choose :)

Mel Gorman
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