On Sun, 22 Apr 2018, Michal Hocko wrote: > On Sat 21-04-18 07:47:57, Matthew Wilcox wrote: > > > > He didn't want to fix vmalloc(GFP_NOIO) > > > > I don't remember that conversation, so I don't know whether I agree with > > his reasoning or not. But we are supposed to be moving away from GFP_NOIO > > towards marking regions with memalloc_noio_save() / restore. If you do > > that, you won't need vmalloc(GFP_NOIO). > > It was basically to detect GFP_NOIO context _inside_ vmalloc and use the > scope API to enforce it there. Does it solve potential problems? Yes it > does. Does it solve any existing report, no I am not aware of any. Is > it a good fix longterm? Absolutely no, because the scope API should be > used _at the place_ where the scope starts rather than a random utility > function. If we are going the easier way now, we will never teach users > to use the API properly. And I am willing to risk to keep a broken > code which we have for years rather than allow a random hack that will > seemingly fix it. > > Btw. I was pretty much explicit with this reasoning when rejecting the > patch. Do you still call that evil? You are making nonsensical excuses. That patch doesn't prevent you from refactoring the kernel and eliminating GFP_NOIO in the long term. You can apply the patch and then continue working on GFP_NOIO refactoring as well as before. > > > he didn't want to fix alloc_pages sleeping when __GFP_NORETRY is used. > > > > The GFP flags are a mess, still. > > I do not remember that one but __GFP_NORETRY is _allowed_ to sleep. And > yes I do _agree_ gfp flags are a mess which is really hard to get fixed > because they are lacking a good design from the very beginning. Fixing > some of those issues today is a completely PITA. It may sleep, but if it sleeps regularly, it slows down swapping (because the swapping code does mempool_alloc and mempool_alloc does __GFP_NORETRY allocation). And there were two INTENTIONAL sleeps with schedule_timeout. You removed one and left the other, claiming that __GFP_NORETRY allocation should sleep. > > > I already said that we can change it from CONFIG_DEBUG_VM to > > > CONFIG_DEBUG_SG - or to whatever other option you may want, just to make > > > sure that it is enabled in distro debug kernels by default. > > > > Yes, and I think that's the right idea. So send a v2 and ignore the > > replies that are clearly relating to an earlier version of the patch. > > Not everybody reads every mail in the thread before responding to one they > > find interesting. Yes, ideally, one would, but sometimes one doesn't. > > And look here. This is yet another ad-hoc idea. We have many users of > kvmalloc which have no relation to SG, yet you are going to control > their behavior by CONFIG_DEBUG_SG? No way! (yeah evil again) Why aren't you constructive and pick up pick up the CONFIG flag? > Really, we have a fault injection framework and this sounds like > something to hook in there. The testing people won't set it up. They install the "kernel-debug" package and run the tests in it. If you introduce a hidden option that no one knows about, no one will use it. > -- > Michal Hocko > SUSE Labs Mikulas
