Re: [PATCH 4/3] mm: drop MMF_OOM_SKIP from exit_mmap
From: Suren Baghdasaryan <surenb@google.com>
Date: 2021-12-09 17:07:12
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On Thu, Dec 9, 2021 at 8:47 AM Michal Hocko [off-list ref] wrote:
On Thu 09-12-21 08:24:04, Suren Baghdasaryan wrote:quoted
On Thu, Dec 9, 2021 at 1:12 AM Michal Hocko [off-list ref] wrote:quoted
Do we want this on top?As we discussed in this thread https://lore.kernel.org/all/YY4snVzZZZYhbigV@dhcp22.suse.cz (local), __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. Thanks!
-- Michal Hocko SUSE Labs