On Mon, Sep 30, 2013 at 6:54 PM, Peter Zijlstra <[email protected]> wrote: > > On Mon, Sep 30, 2013 at 06:48:55PM +0200, Stephane Eranian wrote: > > On Mon, Sep 30, 2013 at 6:15 PM, Peter Zijlstra <[email protected]> > > wrote: > > > On Mon, Sep 30, 2013 at 05:44:41PM +0200, Stephane Eranian wrote: > > >> Hi, > > >> > > >> I was alerted by people trying to use the PERF_RECORD_MMAP2 > > >> record to disambiguate virtual address mappings that there is a case > > >> where the record does not contain enough information. > > >> > > >> As you know, the MMAP2 record adds the major, minor, ino number, > > >> inode generation numbers to a mapping. But it does that only for > > >> file or pseudo -file backed mappings. That covers file mmaps and also > > >> SYSV shared memory segments. > > >> > > >> However there is a another kind of situation that arises in some > > >> multi-process benchmarks where a region of memory is cloned > > >> using VM_CLONE. As such, the virtual addresses match between > > >> the processes but the major, minor, inode, inode generation fields > > >> are all zeroes because there is no inode associated with the mapping. > > >> Yet, it is important for the tool to know the mappings between the > > >> processes are pointing to the same physical data. > > >> > > >> We need to cover this case and I am seeking for advice on how to > > >> best address this need given that we discarded using the plain physical > > >> address for disambiguation. > > > > > > Urgh.. who in his bloody mind is playing VM_CLNOE games that is not > > > pthread_creatE() ? > > > > Some matrix multiply benchmark, I guess. > > So the problem is that we don't have a user visible address space > identifier; with CLONE_THREAD we have the thread group id that acts > like this. But for bare CLONE_VM usage there's nothing afaik.
>From the tool's perspective, the MMAP2 record must contain enough information to identify that the mapping points to the same physical pages in that particular case (multi-process + VM_CLONE). As we have it now all inode-related fields are zero which is useless (indicates: no info). In other words, we need to make up some unique number and stash it in the maj.min,ino triplet somehow. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
