* Oleg Nesterov <oleg@xxxxxxxxxx> wrote: > I didn't read v2 yet, but I'd like to ask a question. > > Why do we need vmalloc_sync_all()? > > It has a single caller, register_die_notifier() which calls it without > any explanation. IMO, this needs a comment at least. Yes, it's used to work around crashes in modular callbacks: if the callbacks happens to be called from within the page fault path, before the vmalloc page fault handler runs, then we have a catch-22 problem. It's rare but not entirely impossible. > I am not sure I understand the changelog in 101f12af correctly, but at first > glance vmalloc_sync_all() is no longer needed at least on x86, do_page_fault() > no longer does notify_die(DIE_PAGE_FAULT). And btw DIE_PAGE_FAULT has no users. > DIE_MNI too... > > Perhaps we can simply kill it on x86? So in theory we could still have it run from DIE_OOPS, and that could turn a survivable kernel crash into a non-survivable one. Note that all of this will go away if we also do the vmalloc fault handling simplification that I discussed with Andy: - this series already makes the set of kernel PGDs strictly monotonically increasing during the lifetime of the x86 kernel - if in a subsequent patch we can synchronize new PGDs right after the vmalloc code creates it, before the area is used - so we can remove vmalloc_fault() altogether [or rather, turn it into a debug warning initially]. vmalloc_fault() is a clever but somewhat fragile complication. - after that we can simply remove vmalloc_sync_all() from x86, because all active vmalloc areas will be fully instantiated, all the time, on x86. Thanks, Ingo -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>