On Thu, Dec 9, 2021 at 9:06 AM Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote: > > On Thu, Dec 9, 2021 at 8:47 AM Michal Hocko <mhocko@xxxxxxxx> wrote: > > > > On Thu 09-12-21 08:24:04, Suren Baghdasaryan wrote: > > > On Thu, Dec 9, 2021 at 1:12 AM Michal Hocko <mhocko@xxxxxxxx> wrote: > > > > > > > > Do we want this on top? > > > > > > As we discussed in this thread > > > https://lore.kernel.org/all/YY4snVzZZZYhbigV@xxxxxxxxxxxxxx, > > > __oom_reap_task_mm in exit_mmap allows oom-reaper/process_mrelease to > > > unmap pages in parallel with exit_mmap without blocking each other. > > > Removal of __oom_reap_task_mm from exit_mmap prevents this parallelism > > > and has a negative impact on performance. So the conclusion of that > > > thread I thought was to keep that part. My understanding is that we > > > also wanted to remove MMF_OOM_SKIP as a follow-up patch but > > > __oom_reap_task_mm would stay. > > > > OK, then we were talking past each other, I am afraid. I really wanted > > to get rid of this oom specific stuff from exit_mmap. It was there out > > of necessity. With a proper locking we can finally get rid of the crud. > > As I've said previously oom reaping has never been a hot path. > > > > If we really want to optimize this path then I would much rather see a > > generic solution which would allow to move the write lock down after > > unmap_vmas. That would require oom reaper to be able to handle mlocked > > memory. > > Ok, let's work on that and when that's done we can get rid of the oom > stuff in exit_mmap. I'll look into this over the weekend and will > likely be back with questions. As promised, I have a question: Any particular reason why munlock_vma_pages_range clears VM_LOCKED before unlocking pages and not after (see: https://elixir.bootlin.com/linux/latest/source/mm/mlock.c#L424)? Seems to me if VM_LOCKED was reset at the end (with proper ordering) then __oom_reap_task_mm would correctly skip VM_LOCKED vmas. https://lore.kernel.org/lkml/20180514064824.534798031@xxxxxxxxxxxxxxxxxxx/ has this explanation: "Since munlock_vma_pages_range() depends on clearing VM_LOCKED from vm_flags before actually doing the munlock to determine if any other vmas are locking the same memory, the check for VM_LOCKED in the oom reaper is racy." but "to determine if any other vmas are locking the same memory" explanation eludes me... Any insights? Thanks, Suren. > Thanks! > > > -- > > Michal Hocko > > SUSE Labs
