* Peter Zijlstra <peterz@xxxxxxxxxxxxx> [2012-04-20 12:14:21]: > On Mon, 2012-04-16 at 23:47 +0200, Oleg Nesterov wrote: > > On 04/16, Peter Zijlstra wrote: > > > > > > On Mon, 2012-04-16 at 01:44 +0200, Oleg Nesterov wrote: > > > > > > > And. I have another reason for down_write() in register/unregister. > > > > I am still not sure this is possible (I had no time to try to > > > > implement), but it seems to me we can kill the uprobe counter in > > > > mm_struct. > > > > > > You mean by making register/unregister down_write, you're exclusive with > > > munmap() > > > > .. and with register/unregister. > > > > Why do we need mm->uprobes_state.count? It is writeonly, except we > > check it in the DIE_INT3 notifier before anything else to avoid the > > unnecessary uprobes overhead. > > and uprobe_munmap(). If we can kill mm->uprobs_state.count, we can do away with uprobe_munmap. Because uprobe_munmap is only around to manage mm->uprobes_state.count. > > > Suppose we kill it, and add the new MMF_HAS_UPROBE flag instead. > > install_breakpoint() sets it unconditionally, > > uprobe_pre_sstep_notifier() checks it. > > Argh, why are MMF_flags part of sched.h.. one would expect those to be > in mm.h or mm_types.h.. somewhere near struct mm. > > > (And perhaps we can stop right here? I mean how often this can > > slow down the debugger which installs int3 in the same mm?) > > > > Now we need to clear MMF_HAS_UPROBE somehowe, when the last > > uprobe goes away. Lets ignore uprobe_map/unmap for simplicity. > > > > - We add another flag, MMF_UPROBE_RECALC, it is set by > > remove_breakpoint(). > > > > - We change handle_swbp(). Ignoring all details it does: > > > > if (find_uprobe(vaddr)) > > process_uprobe(); > > else if (test_bit(MMF_HAS_UPROBE) && test_bit(MMF_UPROBE_RECALC)) > > recalc_mmf_uprobe_flag(); > > > > where recalc_mmf_uprobe_flag() checks all vmas and either > > clears both flags or MMF_UPROBE_RECALC only. > > > > This is the really slow O(n) path, but it can only happen after > > unregister, and only if we hit another non-uprobe breakpoint > > in the same mm. > > > > Something like this. What do you think? > > I think I can live with the simple set MMF_HAS_UPROBE and leave it at > that. The better optimization seems to be to not install breakpoints > when ->filter() excludes the task.. > > It looks like we currently install the breakpoint unconditionally and > only ->filter() once we hit the breakpoint, which is somewhat > sub-optimal. > Yes, We install breakpoints unconditionally, I think we had already discussed this and Oleg had proposed a solution too. http://lkml.org/lkml/2011/6/16/470 where we move the mm struct from task struct to signal struct. -- Thanks and Regards Srikar -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>