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Thu, 17 Sep 2026 11:11:18 -0700 (PDT) Received: from localhost ([2a03:2880:2ff:51::]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-872025dd04csm3272663b3a.60.2026.09.17.11.11.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 17 Sep 2026 11:11:17 -0700 (PDT) From: Stanislav Fomichev X-Google-Original-From: Stanislav Fomichev To: netdev@vger.kernel.org Cc: davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, sdf@fomichev.me, bobbyeshleman@meta.com, almasrymina@google.com, linux-kernel@vger.kernel.org Subject: [PATCH net-next v3 1/3] net: devmem: replace gen_pool with freelist Date: Thu, 17 Sep 2026 11:11:14 -0700 Message-ID: <20260917181116.3319017-2-sdf@fomichev.me> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260917181116.3319017-1-sdf@fomichev.me> References: <20260917181116.3319017-1-sdf@fomichev.me> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit devmem only needs fixed-size net_iov allocations for each dma-buf binding. The gen_pool tracks the same free set indirectly through DMA addresses, which makes devmem depend on the generic allocator even though the users are fixed-size net_iov chunks. Mirror the io_uring zcrx model more closely by keeping a binding-level freelist protected by spin_lock_bh(). Use a single net_iov_area owner for the binding, populate each net_iov's DMA address while walking the SG table, and check at teardown that all net_iovs have returned to the freelist. Validate the DMA-BUF size against the net_iov size up front and derive the RX and TX entry count from it, avoiding a separate SG-table pass. Drop the NET_DEVMEM select of GENERIC_ALLOCATOR now that devmem no longer calls gen_pool APIs. Signed-off-by: Stanislav Fomichev --- net/Kconfig | 1 - net/core/devmem.c | 182 +++++++++++++++++++++------------------------- net/core/devmem.h | 15 ++-- 3 files changed, 88 insertions(+), 110 deletions(-) diff --git a/net/Kconfig b/net/Kconfig index e38477393551..76ab44aa439a 100644 --- a/net/Kconfig +++ b/net/Kconfig @@ -68,7 +68,6 @@ config SKB_EXTENSIONS config NET_DEVMEM def_bool y - select GENERIC_ALLOCATOR depends on DMA_SHARED_BUFFER depends on PAGE_POOL diff --git a/net/core/devmem.c b/net/core/devmem.c index f4d60654ce7f..2ac9d74010a9 100644 --- a/net/core/devmem.c +++ b/net/core/devmem.c @@ -8,7 +8,6 @@ */ #include -#include #include #include #include @@ -30,23 +29,13 @@ static DEFINE_XARRAY_FLAGS(net_devmem_dmabuf_bindings, XA_FLAGS_ALLOC1); static const struct memory_provider_ops dmabuf_devmem_ops; -static void net_devmem_dmabuf_free_chunk_owner(struct gen_pool *genpool, - struct gen_pool_chunk *chunk, - void *not_used) +static void +net_devmem_dmabuf_free_chunk_owner(struct dmabuf_genpool_chunk_owner *owner) { - struct dmabuf_genpool_chunk_owner *owner = chunk->owner; - - kvfree(owner->area.niovs); - kfree(owner); -} - -static dma_addr_t net_devmem_get_dma_addr(const struct net_iov *niov) -{ - struct dmabuf_genpool_chunk_owner *owner; - - owner = net_devmem_iov_to_chunk_owner(niov); - return owner->base_dma_addr + - ((dma_addr_t)net_iov_idx(niov) << owner->binding->niov_shift); + if (owner) { + kvfree(owner->area.niovs); + kfree(owner); + } } static void net_devmem_dmabuf_binding_release(struct percpu_ref *ref) @@ -62,24 +51,20 @@ void __net_devmem_dmabuf_binding_free(struct work_struct *wq) { struct net_devmem_dmabuf_binding *binding = container_of(wq, typeof(*binding), unbind_w); - size_t size, avail; - - gen_pool_for_each_chunk(binding->chunk_pool, - net_devmem_dmabuf_free_chunk_owner, NULL); - - size = gen_pool_size(binding->chunk_pool); - avail = gen_pool_avail(binding->chunk_pool); - - if (!WARN(size != avail, "can't destroy genpool. size=%zu, avail=%zu", - size, avail)) - gen_pool_destroy(binding->chunk_pool); + if (binding->freelist) + WARN(binding->free_count != binding->chunk_owner->area.num_niovs, + "destroying dmabuf binding with outstanding net_iovs: total=%zu, free=%zu", + binding->chunk_owner->area.num_niovs, + binding->free_count); + net_devmem_dmabuf_free_chunk_owner(binding->chunk_owner); dma_buf_unmap_attachment_unlocked(binding->attachment, binding->sgt, binding->direction); dma_buf_detach(binding->dmabuf, binding->attachment); dma_buf_put(binding->dmabuf); xa_destroy(&binding->bound_rxqs); percpu_ref_exit(&binding->ref); + kvfree(binding->freelist); kvfree(binding->tx_vec); kfree(binding); } @@ -87,21 +72,15 @@ void __net_devmem_dmabuf_binding_free(struct work_struct *wq) struct net_iov * net_devmem_alloc_dmabuf(struct net_devmem_dmabuf_binding *binding) { - struct dmabuf_genpool_chunk_owner *owner; - unsigned long dma_addr; struct net_iov *niov; - ssize_t offset; - ssize_t index; - - dma_addr = gen_pool_alloc_owner(binding->chunk_pool, - 1UL << binding->niov_shift, - (void **)&owner); - if (!dma_addr) + spin_lock_bh(&binding->freelist_lock); + if (unlikely(!binding->free_count)) { + spin_unlock_bh(&binding->freelist_lock); return NULL; + } - offset = dma_addr - owner->base_dma_addr; - index = offset >> binding->niov_shift; - niov = &owner->area.niovs[index]; + niov = binding->freelist[--binding->free_count]; + spin_unlock_bh(&binding->freelist_lock); niov->desc.pp_magic = 0; niov->desc.pp = NULL; @@ -113,14 +92,16 @@ net_devmem_alloc_dmabuf(struct net_devmem_dmabuf_binding *binding) void net_devmem_free_dmabuf(struct net_iov *niov) { struct net_devmem_dmabuf_binding *binding = net_devmem_iov_binding(niov); - unsigned long dma_addr = net_devmem_get_dma_addr(niov); - size_t niov_size = 1UL << binding->niov_shift; - if (WARN_ON(!gen_pool_has_addr(binding->chunk_pool, dma_addr, - niov_size))) + spin_lock_bh(&binding->freelist_lock); + if (WARN_ON_ONCE(binding->free_count >= + binding->chunk_owner->area.num_niovs)) { + spin_unlock_bh(&binding->freelist_lock); return; + } - gen_pool_free(binding->chunk_pool, dma_addr, niov_size); + binding->freelist[binding->free_count++] = niov; + spin_unlock_bh(&binding->freelist_lock); } void net_devmem_unbind_dmabuf(struct net_devmem_dmabuf_binding *binding) @@ -194,12 +175,15 @@ net_devmem_bind_dmabuf(struct net_device *dev, void *vdev, struct netlink_ext_ack *extack) { struct net_devmem_dmabuf_binding *binding; + struct dmabuf_genpool_chunk_owner *owner; size_t niov_size = 1UL << niov_shift; static u32 id_alloc_next; struct scatterlist *sg; struct dma_buf *dmabuf; - unsigned int sg_idx, i; - unsigned long virtual; + unsigned int sg_idx; + size_t total_niovs; + size_t niov_idx; + size_t i; int err; if (!dma_dev) { @@ -249,33 +233,55 @@ net_devmem_bind_dmabuf(struct net_device *dev, void *vdev, goto err_detach; } + if (!IS_ALIGNED(dmabuf->size, niov_size)) { + err = -EINVAL; + NL_SET_ERR_MSG_FMT(extack, + "dmabuf size %zu not aligned to niov size %zu", + dmabuf->size, niov_size); + goto err_unmap; + } + + total_niovs = dmabuf->size >> niov_shift; if (direction == DMA_TO_DEVICE) { - if (!IS_ALIGNED(dmabuf->size, PAGE_SIZE)) { - err = -EINVAL; - NL_SET_ERR_MSG(extack, "TX dma-buf size must be a multiple of PAGE_SIZE"); + binding->tx_vec = kvmalloc_objs(struct net_iov *, total_niovs); + if (!binding->tx_vec) { + err = -ENOMEM; goto err_unmap; } - binding->tx_vec = kvmalloc_objs(struct net_iov *, - dmabuf->size / PAGE_SIZE); - if (!binding->tx_vec) { + } else { + spin_lock_init(&binding->freelist_lock); + binding->freelist = kvmalloc_array(total_niovs, + sizeof(binding->freelist[0]), + GFP_KERNEL); + if (!binding->freelist) { err = -ENOMEM; goto err_unmap; } } + owner = kzalloc_node(sizeof(*owner), GFP_KERNEL, + dev_to_node(&dev->dev)); + if (!owner) { + err = -ENOMEM; + goto err_free_freelist; + } - binding->chunk_pool = gen_pool_create(niov_shift, - dev_to_node(&dev->dev)); - if (!binding->chunk_pool) { + owner->area.base_virtual = 0; + owner->area.num_niovs = total_niovs; + owner->binding = binding; + owner->area.niovs = kvmalloc_objs(*owner->area.niovs, + owner->area.num_niovs); + if (!owner->area.niovs) { err = -ENOMEM; - goto err_tx_vec; + goto err_free_owner; } + binding->chunk_owner = owner; - virtual = 0; + niov_idx = 0; for_each_sgtable_dma_sg(binding->sgt, sg, sg_idx) { dma_addr_t dma_addr = sg_dma_address(sg); - struct dmabuf_genpool_chunk_owner *owner; size_t len = sg_dma_len(sg); struct net_iov *niov; + size_t nr_niovs; if (!IS_ALIGNED(dma_addr, niov_size) || !IS_ALIGNED(len, niov_size)) { @@ -283,64 +289,40 @@ net_devmem_bind_dmabuf(struct net_device *dev, void *vdev, NL_SET_ERR_MSG_FMT(extack, "dmabuf sg entry (addr=%pad, len=%zu) not aligned to niov size %zu", &dma_addr, len, niov_size); - goto err_free_chunks; - } - - owner = kzalloc_node(sizeof(*owner), GFP_KERNEL, - dev_to_node(&dev->dev)); - if (!owner) { - err = -ENOMEM; - goto err_free_chunks; + goto err_free_chunk_owner; } - owner->area.base_virtual = virtual; - owner->base_dma_addr = dma_addr; - owner->area.num_niovs = len >> niov_shift; - owner->binding = binding; - - err = gen_pool_add_owner(binding->chunk_pool, dma_addr, - dma_addr, len, dev_to_node(&dev->dev), - owner); - if (err) { - kfree(owner); - err = -EINVAL; - goto err_free_chunks; - } - - owner->area.niovs = kvmalloc_objs(*owner->area.niovs, - owner->area.num_niovs); - if (!owner->area.niovs) { - err = -ENOMEM; - goto err_free_chunks; - } - - for (i = 0; i < owner->area.num_niovs; i++) { - niov = &owner->area.niovs[i]; + nr_niovs = len >> niov_shift; + for (i = 0; i < nr_niovs; i++, niov_idx++) { + niov = &owner->area.niovs[niov_idx]; net_iov_init(niov, &owner->area, NET_IOV_DMABUF); page_pool_set_dma_addr_netmem(net_iov_to_netmem(niov), - net_devmem_get_dma_addr(niov)); + dma_addr); if (direction == DMA_TO_DEVICE) - binding->tx_vec[owner->area.base_virtual / PAGE_SIZE + i] = niov; + binding->tx_vec[niov_idx] = niov; + else + binding->freelist[binding->free_count++] = niov; + dma_addr += niov_size; } - - virtual += len; } err = xa_alloc_cyclic(&net_devmem_dmabuf_bindings, &binding->id, binding, xa_limit_32b, &id_alloc_next, GFP_KERNEL); if (err < 0) - goto err_free_chunks; + goto err_free_chunk_owner; list_add(&binding->list, &priv->bindings); return binding; -err_free_chunks: - gen_pool_for_each_chunk(binding->chunk_pool, - net_devmem_dmabuf_free_chunk_owner, NULL); - gen_pool_destroy(binding->chunk_pool); -err_tx_vec: +err_free_chunk_owner: + net_devmem_dmabuf_free_chunk_owner(binding->chunk_owner); + goto err_free_freelist; +err_free_owner: + kfree(owner); +err_free_freelist: + kvfree(binding->freelist); kvfree(binding->tx_vec); err_unmap: dma_buf_unmap_attachment_unlocked(binding->attachment, binding->sgt, diff --git a/net/core/devmem.h b/net/core/devmem.h index 4a293a7d1149..db2eb6372aee 100644 --- a/net/core/devmem.h +++ b/net/core/devmem.h @@ -14,6 +14,7 @@ #include struct netlink_ext_ack; +struct dmabuf_genpool_chunk_owner; struct net_devmem_dmabuf_binding { struct dma_buf *dmabuf; @@ -26,7 +27,7 @@ struct net_devmem_dmabuf_binding { * dereferenced. */ void *vdev; - struct gen_pool *chunk_pool; + struct dmabuf_genpool_chunk_owner *chunk_owner; /* Protect dev */ struct mutex lock; @@ -57,6 +58,10 @@ struct net_devmem_dmabuf_binding { /* rxq's this binding is active on. */ struct xarray bound_rxqs; + spinlock_t freelist_lock ____cacheline_aligned_in_smp; + size_t free_count; + struct net_iov **freelist; + /* ID of this binding. Globally unique to all bindings currently * active. */ @@ -77,17 +82,9 @@ struct net_devmem_dmabuf_binding { }; #if defined(CONFIG_NET_DEVMEM) -/* Owner of the dma-buf chunks inserted into the gen pool. Each scatterlist - * entry from the dmabuf is inserted into the genpool as a chunk, and needs - * this owner struct to keep track of some metadata necessary to create - * allocations from this chunk. - */ struct dmabuf_genpool_chunk_owner { struct net_iov_area area; struct net_devmem_dmabuf_binding *binding; - - /* dma_addr of the start of the chunk. */ - dma_addr_t base_dma_addr; }; void __net_devmem_dmabuf_binding_free(struct work_struct *wq); -- 2.53.0-Meta