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Tue, 01 Sep 2026 13:59:49 -0700 (PDT) Date: Tue, 1 Sep 2026 16:59:46 -0400 From: Johannes Weiner To: Michal Hocko Cc: David Stevens , Shakeel Butt , Roman Gushchin , Muchun Song , Andrew Morton , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] memcg: Don't call schedule_work when no spinning is allowed Message-ID: <20260901205946.GL3004@cmpxchg.org> References: <20260831234339.280376-1-stevensd@google.com> <20260901142552.GG3004@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: C1AD016000B X-Stat-Signature: ujcbc6z8ccoup7598ipz9iahdtah8iar X-Rspam-User: X-HE-Tag: 1788296391-967480 X-HE-Meta: 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 1IJq3Dha R/vY01CzLfL547t+WnW0mvGtRC57ktSWD73iKheX3KW/KAF6CT2CSDNCCpnl3rVaycZaVaabbQpmDnTxy6pZEnWtUXP7SCITaX7xu044/P5ycT6d00Xv08YhT7BL2BJtL4vYXXMF9GGTVtaKEuN0D057GsWAcWtp1dPlAUgiewdqtjN4TpwS98HesIxj0n9Z8Zc3Lji3UQwPKyxvmPJB3PPQqcGJGb+7ExLW/ZwrRyjAD0/6+06fNtLATXi4oxfMX17od11HOmlmxXxM1os+wqcpAs4vsCQ1NPSFfd3kqjlrfEX3V33cIy1+C3DMOQyurA/2J3wnxH+11rlhS0rAm4rGqY5MrwJFc5tx4MW2voGxqJe0K4zV9JHL9mtTCltWtL+b1FzdSGhGEgaLZINLdfSF9BOYJ/1d9s6ynJS8JTwLN/gQNUNt3oZlX3inLTFpl6e/I Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Sep 01, 2026 at 05:42:30PM +0200, Michal Hocko wrote: > On Tue 01-09-26 10:25:52, Johannes Weiner wrote: > > On Mon, Aug 31, 2026 at 06:04:57PM -0700, David Stevens wrote: > [...] > > > There would be no guarantee that memcg reclaim would ever be > > > triggered, which also would also stop MEMCG_HIGH events from being > > > generated. Overall that seems a more serious than just dropping > > > userspace notifications like is done for MEMCG_MAX. > > > > I'm leaning that way too. It's an indefinite error, and it's a freely > > programmable surface. > > I am really curious about the indefinite error side of things. It has > been my understanding that these NMI safe charges are a) rare and b) > there is userspace running so eventually any discrepancies would > resolve so the excess is temporary. So I think the question is what limits the error in both space and time. When you say it's rare and userspace fixes it, it basically means the answer is: luck of the common case. But that doesn't help the worst case that can be triggered. Like I said, if we need to have code to handle that !allow_spinning case anyway, I'd rather just have a few lines of working code than a (lengthy) comment explaining the luck of the common case.