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Thu, 26 Feb 2026 10:03:34 -0800 (PST) MIME-Version: 1.0 References: <20260225-dma-buf-heaps-as-modules-v1-0-2109225a090d@kernel.org> <20260226-adaptable-vermilion-nautilus-0aa6f0@penduick> In-Reply-To: <20260226-adaptable-vermilion-nautilus-0aa6f0@penduick> From: John Stultz Date: Thu, 26 Feb 2026 10:03:21 -0800 X-Gm-Features: AaiRm538ftOfa1UyUjDoV9Yd7b0SRwtnSHBghCEM_shajRcZSxbK21W611Pqdkc Message-ID: Subject: Re: [PATCH 0/7] dma-buf: heaps: Turn heaps into modules To: Maxime Ripard Cc: Sumit Semwal , Benjamin Gaignard , Brian Starkey , "T.J. Mercier" , =?UTF-8?Q?Christian_K=C3=B6nig?= , Marek Szyprowski , Robin Murphy , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org, iommu@lists.linux.dev, linux-mm@kvack.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 0B29580016 X-Stat-Signature: 7ryqumkjneaacoejboqxu36wy1u595d5 X-HE-Tag: 1772129328-798019 X-HE-Meta: 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 1J/J1mbr atTxJ4EKbkGQjLO46D1Hxxt7S4j/kBYpkUX2jxHdqJPJbbaNmR1GNfHENpru0DWA8QOrZOBumdR3bKiaM7paVsLkYwb7BVIzwnwpH/f3LFbmG+ZFipM0WAXbek0Vy2fnEtrsX8PdnyUFxDiIZjWvRzGAugytUJWdjdIzxwuNuho0oEqyVCOVAD9Hw2E3bW7Ep+W9M7Ng4maG91s8hUbyre7fMrEqqVq+BsZi+69jO97yrjlv/FUFge9qCgdgq50SnJSzJvc9XBjIm/l2PcrgGGT8W/K9B7m62vxHCOFedhmKKMxiLFzntYftQuAq2PviN0YQOKueun10MmA6Y8V93bddwvGL3HAZFFwGJdmJmyuAAzEbsehkNFiScJWEUqpWR/GOv81nvx00hfyQAA2NxPSw4R/W4sHy5GGLWxSdk4wZIGoj+UFcfs9ttUus5G0y7suLRKPS+Dz03CFCIwqTKieaRXkfrdkQ+4ZE1iIKqREMrYR1MWYokzZye+znyZtowjqJv Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Feb 26, 2026 at 2:18=E2=80=AFAM Maxime Ripard = wrote: > On Wed, Feb 25, 2026 at 10:51:30AM -0800, John Stultz wrote: > > So heaps-as-modules is common in the Android kernels, and was > > attempted to be upstreamed long ago: > > https://lore.kernel.org/lkml/20191025234834.28214-1-john.stultz@linar= o.org/ > > > > And it got a fairly chilly reception, but maybe having the additional > > optee heap (as well as other proposed heaps) might sway folks on this > > now. > > I didn't know that Android was using heap as modules only, but I'd say > that it's even more of a reason to upstream it then. > > > There is also the kref bits you might need (which Android still carries= ): > > https://lore.kernel.org/lkml/20200725032633.125006-1-john.stultz@lina= ro.org/ > > I'm curious about this one though. It looks like you add refcounting, > but never really get the references anywhere. What was your intent, that > on every allocation the buffer would get a reference to the heap so we > avoid removing a heap with allocated buffers? Oh, apologies I mixed this up. You can ignore that suggestion. In Android, once folks were familiar with thinking about dma-buf heaps, some (out of tree) drivers wanted to be able to internally allocate from a given heap (somewhat of a hold-over from the old ION drivers). So we have a convenience patch to provide that: https://android.googlesource.com/kernel/common/+/8e1ec97355ef9927e82ec18= c98312bdcd80bf289%5E%21/ And since we return a dma_heap to the driver to allocate against: https://android.googlesource.com/kernel/common/+/fc1310ebf8fe25ea7b983400= e6fa41f5a6d11966%5E%21/ The kref bit is to make sure we're doing proper reference counting on that shared pointer. This ended up getting bundled together along with the heaps-as-modules changes in our out-of-tree changes, and I just confused its use here. thanks -john