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Mon, 15 Dec 2025 02:51:41 -0800 (PST) Received: from localhost ([82.66.159.240]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-47a8f6f3e78sm69652615e9.3.2025.12.15.02.51.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 15 Dec 2025 02:51:40 -0800 (PST) Date: Mon, 15 Dec 2025 11:51:38 +0100 From: Maxime Ripard To: "T.J. Mercier" Cc: Eric Chanudet , Sumit Semwal , Benjamin Gaignard , Brian Starkey , John Stultz , Christian Koenig , linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org, "open list:MEMORY MANAGEMENT" Subject: Re: [PATCH] dma-buf: system_heap: account for system heap allocation in memcg Message-ID: <20251215-sepia-husky-of-eternity-ecf0ce@penduick> References: <20251211193106.755485-2-echanude@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha384; protocol="application/pgp-signature"; boundary="u7gkqqtkk3esv3ha" Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Queue-Id: AAC81140005 X-Rspamd-Server: rspam10 X-Stat-Signature: 834peu3rfewkzg1jyic7izrtr86h94dw X-HE-Tag: 1765795906-365553 X-HE-Meta: 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 Z1dLJyQ0 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: --u7gkqqtkk3esv3ha Content-Type: text/plain; protected-headers=v1; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Subject: Re: [PATCH] dma-buf: system_heap: account for system heap allocation in memcg MIME-Version: 1.0 Hi TJ, On Fri, Dec 12, 2025 at 08:25:19AM +0900, T.J. Mercier wrote: > On Fri, Dec 12, 2025 at 4:31=E2=80=AFAM Eric Chanudet wrote: > > > > The system dma-buf heap lets userspace allocate buffers from the page > > allocator. However, these allocations are not accounted for in memcg, > > allowing processes to escape limits that may be configured. > > > > Pass the __GFP_ACCOUNT for our allocations to account them into memcg. >=20 > We had a discussion just last night in the MM track at LPC about how > shared memory accounted in memcg is pretty broken. Without a way to > identify (and possibly transfer) ownership of a shared buffer, this > makes the accounting of shared memory, and zombie memcg problems > worse. :\ Are there notes or a report from that discussion anywhere? The way I see it, the dma-buf heaps *trivial* case is non-existent at the moment and that's definitely broken. Any application can bypass its cgroups limits trivially, and that's a pretty big hole in the system. The shared ownership is indeed broken, but it's not more or less broken than, say, memfd + udmabuf, and I'm sure plenty of others. So we really improve the common case, but only make the "advanced" slightly more broken than it already is. Would you disagree? Maxime --u7gkqqtkk3esv3ha Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iJUEABMJAB0WIQTkHFbLp4ejekA/qfgnX84Zoj2+dgUCaT/oOgAKCRAnX84Zoj2+ dkxfAX4ve8AMEp5rGVxqWdx7mP32EEUlTe7oGqgQsZGk3gdf9G5zzO3162M7qdiD 3jlaGbUBfRHozRNiBmCNTKcExXO6w9Ygjiy0DBe+Vt/PkW0DZjejxbuLLNtgH70W djcO8jaBRA== =lq40 -----END PGP SIGNATURE----- --u7gkqqtkk3esv3ha--