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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id b2sm28272827qtq.95.2022.01.03.13.16.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 03 Jan 2022 13:16:37 -0800 (PST) Date: Mon, 3 Jan 2022 13:16:21 -0800 (PST) From: Hugh Dickins X-X-Sender: hugh@ripple.anvils To: Michal Hocko cc: Suren Baghdasaryan , Johannes Weiner , Andrew Morton , David Rientjes , Matthew Wilcox , Roman Gushchin , Rik van Riel , Minchan Kim , "Kirill A. Shutemov" , Andrea Arcangeli , Christian Brauner , Christoph Hellwig , Oleg Nesterov , David Hildenbrand , Jann Horn , Shakeel Butt , Andy Lutomirski , Christian Brauner , Florian Weimer , Jan Engelhardt , Tim Murray , Vlastimil Babka , linux-mm , LKML , kernel-team Subject: Re: [PATCH 4/3] mm: drop MMF_OOM_SKIP from exit_mmap In-Reply-To: Message-ID: <35c340a6-96f-28a0-2b7b-2f9fbddc01f@google.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 3 Jan 2022, Michal Hocko wrote: > On Thu 30-12-21 09:29:40, Suren Baghdasaryan wrote: > > On Thu, Dec 30, 2021 at 12:24 AM Michal Hocko wrote: > > > > > > It would be really great to make unlock_range oom reaper aware IMHO. > > > > What exactly do you envision? Say unlock_range() knows that it's > > racing with __oom_reap_task_mm() and that calling follow_page() is > > unsafe without locking, what should it do? > > My original plan was to make the page lock conditional and use > trylocking from the oom reaper (aka lockless context). It is OK to > simply bail out and leave some mlocked memory behind if there is a > contention on a specific page. The overall objective is to free as much > memory as possible, not all of it. > > IIRC Hugh was not a fan of this approach and he has mentioned that the > lock might not be even really needed and that the area would benefit > from a clean up rather than oom reaper specific hacks. I do tend to > agree with that. I just never managed to find any spare time for that > though and heavily mlocked oom victims tend to be really rare. I forget when that was, and what I had in mind at that time. But yes, by now I am very sure that munlocking needs a cleanup. And I do have that cleanup (against a much older tree), but never the time to rebase or post or shepherd it through N revisions. It was 22 files changed, 464 insertions, 706 deletions: which is too much to help with this immediate oom reaper question. I'd better not drive this discussion further off-course; but it pains me to see munlock_vma_pages obstructing, knowing there's a better way. I wonder: what if I were to steal time and promise to post a rebased series against 5.17-rc1 or rc2: not support it thereafter, but might there be someone to pick it up and shepherd it through? But there's no answer to that, without you seeing what it's like. Hugh