On Tue, Apr 13, 2010 at 08:02:54PM +0200, Peter Zijlstra wrote: > On Tue, 2010-04-13 at 10:57 -0700, Roland Dreier wrote: > > Are those system calls the only possible way that virtual to physical > > mappings can change? Can't page migration or something like that > > potentially affect things? And even if you did have hooks into every > > system call that mattered (keep in mind that relying on glibc is not > > enough, since an MPI application may not use glibc) would decoding them > > and figuring out what happened really be preferable to a single event > > type that tells you exactly what address range was affected? > > Yeah, virtual<->physical maps can change through swapping, page > migration, memory compaction, huge-page aggregation (the latter two not > yet being upstream). > > Even mlock() doesn't pin virtual<->physical maps. Pages registered for RDMA are GUPed so no method above should touch them. Fork+cow or unmap/map on the other hand can change virtual<->physical maps. GUPed pages are still GUPed, but they are no longer mapped into process' virtual address space. MPI copes with Fork+cow by marking registered memory as MADV_DONTFORK.
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