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Date: Thu, 29 Jun 2017 10:09:10 +0200 From: Michal Hocko <mhocko@...nel.org> To: Prakash Sangappa <prakash.sangappa@...cle.com> Cc: Mike Rapoport <rppt@...ux.vnet.ibm.com>, linux-kernel@...r.kernel.org, linux-mm@...ck.org, Andrea Arcangeli <aarcange@...hat.com>, Mike Kravetz <mike.kravetz@...cle.com>, Dave Hansen <dave.hansen@...el.com>, Christoph Hellwig <hch@...radead.org>, linux-api@...r.kernel.org Subject: Re: [RFC PATCH] userfaultfd: Add feature to request for a signal delivery On Wed 28-06-17 11:23:32, Prakash Sangappa wrote: > > > On 6/28/17 6:18 AM, Mike Rapoport wrote: [...] > >I've just been thinking that maybe it would be possible to use > >UFFD_EVENT_REMOVE for this case. We anyway need to implement the generation > >of UFFD_EVENT_REMOVE for the case of hole punching in hugetlbfs for > >non-cooperative userfaultfd. It could be that it will solve your issue as > >well. > > > > Will this result in a signal delivery? > > In the use case described, the database application does not need any event > for hole punching. Basically, just a signal for any invalid access to > mapped area over holes in the file. OK, but it would be better to think that through for other potential usecases so that this doesn't end up as a single hugetlb feature. E.g. what should happen if a regular anonymous memory gets swapped out? Should we deliver signal as well? How does userspace tell whether this was a no backing page from unavailable backing page? -- Michal Hocko SUSE Labs
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