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From:   Matthew Wilcox <willy@infradead.org>
To:     Axel Rasmussen <axelrasmussen@google.com>
Cc:     Alexander Viro <viro@zeniv.linux.org.uk>,
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Subject: Re: [PATCH v5 05/10] userfaultfd: add minor fault registration mode
Message-ID: <20210212222145.GB2858050@casper.infradead.org>
References: <20210210212200.1097784-1-axelrasmussen@google.com>
 <20210210212200.1097784-6-axelrasmussen@google.com>
 <CAJHvVch8jmqu=Hi9=1CHzPHJfZCRvSb6g7xngSBDQ_nDfSj-gA@mail.gmail.com>
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On Thu, Feb 11, 2021 at 11:28:09AM -0800, Axel Rasmussen wrote:
> Ah, I had added this just after VM_UFFD_WP, without noticing that this
> would be sharing a bit with VM_LOCKED. That seems like not such a
> great idea.
> 
> I don't see another unused bit, and I don't see some other obvious
> candidate to share with. So, the solution that comes to mind is

it'd be even better if you didn't use the last unused bit for UFFD_WP.
not sure how feasible that is, but you can see we're really short on
bits here.