On Fri, 15 Jun 2018, Michal Hocko wrote: > On Fri 15-06-18 07:35:07, Mikulas Patocka wrote: > > > > Because mempool uses it. Mempool uses allocations with "GFP_NOIO | > > __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN". An so dm-bufio uses > > these flags too. dm-bufio is just a big mempool. > > This doesn't answer my question though. Somebody else is doing it is not > an explanation. Prior to your 41c73a49df31 there was no GFP_NOIO > allocation AFAICS. So why do you really need it now? Why cannot you dm-bufio always used "GFP_NOIO | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN" since the kernel 3.2 when it was introduced. In the kernel 4.10, dm-bufio was changed so that it does GFP_NOWAIT allocation, then drops the lock and does GFP_NOIO with the dropped lock (because someone was likely experiencing the same issue that is reported in this thread) - there are two commits that change it - 9ea61cac0 and 41c73a49df31. > simply keep retrying GFP_NOWAIT with your own throttling? > > Note that I am not trying to say that 41c73a49df31, I am merely trying > to understand why this blocking allocation is done in the first place. > > > If you argue that these flags are incorrect - then fix mempool_alloc. > > AFAICS there is no report about mempool_alloc stalling here. Maybe this If the page allocator can stall dm-bufio, it can stall mempool_alloc as well. dm-bufio is just bigger, so it will hit this bug sooner. > is the same class of problem, honestly, I dunno. And I've already said > that stalling __GFP_NORETRY might be a good way around that but that > needs much more consideration and existing users examination. I am not > aware anybody has done that. Doing changes like that based on a single > user is certainly risky. Why don't you set any rules how these flags should be used? If you use GFP_NOIO | __GFP_NORETRY in your own code and blame other people for doing so - you are as much evil as Linus, who praised people for reverse-engineering hardware and blamed them for reverse-engineering bitkeeper :-) Mikulas -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
