Re: [PATCH 0/4] mm/hugetlb: Early cow on fork, and a few cleanups

Gal Pressman
2021-02-04T14:37:54Z

On 03/02/2021 23:08, Peter Xu wrote:
> As reported by Gal [1], we still miss the code clip to handle early cow for
>
> hugetlb case, which is true. Again, it still feels odd to fork() after using a
>
> few huge pages, especially if they're privately mapped to me.. However I do
>
> agree with Gal and Jason in that we should still have that since that'll
>
> complete the early cow on fork effort at least, and it'll still fix issues
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> where buffers are not well under control and not easy to apply MADV_DONTFORK.
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>
>
> The first two patches (1-2) are some cleanups I noticed when reading into the
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> hugetlb reserve map code. I think it's good to have but they're not necessary
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> for fixing the fork issue.
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>
>
> The last two patches (3-4) is the real fix.
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>
>
> I tested this with a fork() after some vfio-pci assignment, so I'm pretty sure
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> the page copy path could trigger well (page will be accounted right after the
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> fork()), but I didn't do data check since the card I assigned is some random
>
> nic. Gal, please feel free to try this if you have better way to verify the
>
> series.

Thanks Peter, once v2 is submitted I'll pull the patches and we'll run the tests
that discovered the issue to verify it works.