On Tue, Jul 30, 2013 at 10:51:46AM +0200, Stephane Eranian wrote: > On Tue, Jul 30, 2013 at 10:37 AM, Peter Zijlstra <pet...@infradead.org> wrote: > > On Tue, Jul 30, 2013 at 10:02:01AM +0200, Stephane Eranian wrote: > >> > Ahh. We don't put the useful bits in the mmap event; we'll need to fix > >> > that too then ;-) > >> > > >> > Doing so is going to be a bit of a bother since we use the tail of > >> > PERF_RECORD_MMAP for filenames and thus aren't particularly extensible. > >> > > >> > This would mean doing something like PERF_RECORD_MMAP2 and some means > >> > for userspace to requrest the new events instead of the old one. > >> > > >> Tracking mmaps even for shmat() won't cover the paging cases. When you > >> page a > >> page back in, it most likely gets a different physical page. How would > >> we track that > >> case too using the same approach? > > > > It doesn't matter. Even if a page ends up being a different physical > > page, it will always be the same sb:inode:pgoffset. You should be able > > to always uniquely identify a (shared) page by that triplet. > > > Ok, so you're saying that triplet uniquely identifies a virtual page > regardless of > the physical page it is mapped onto. If the physical page changes because > of paging, we keep the same triplet and therefore we can still detect the > false > sharing.
Exactly. > > So if we create a net MMAP record that includes the device (substitute > > for the superblock) and inode information we should be good. > > I will try that. I am not familiar with mm, so where do we find the > device? Inside > the vma? Take a peek at fs/proc/task_mmu.c:show_map_vma(), its the code used to print /proc/$PID/maps and displays all stuff we want. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
