dma-heap already supports charging a specific cgroup at allocation time via charge_fd in DMA_HEAP_IOCTL_ALLOC. However, dma-bufs can originate from any exporter (DRM, V4L2, etc.), and the allocator may not know the final owner at allocation time.
Add DMA_BUF_IOCTL_XFER_CHARGE to transfer a dma-buf's memcg charge to a different cgroup after allocation. The target is identified by charge_fd, which may be a cgroupfd or a pidfd.
The transfer charges the new cgroup before uncharging the old one, preserving the original charge on failure. An atomic cmpxchg on dmabuf->memcg prevents races with concurrent transfers.
Not all dma-buf exporters back their buffers with reclaimable system memory. Some represent device registers, VRAM, or carved-out pools where size is not a meaningful memory cost. Add a memcg_account flag to dma_buf_export_info that exporters set when their buffers should participate in memcg accounting. The xfer ioctl returns -EOPNOTSUPP for buffers that do not set the flag. Currently only the system heap sets it, other exporters can opt in as needed.
Usage example: int cg_fd = open("/sys/fs/cgroup/clients/app1", O_RDONLY | O_DIRECTORY);
struct dma_buf_transfer_charge xfer = { .charge_fd = cg_fd, }; ioctl(dmabuf_fd, DMA_BUF_IOCTL_XFER_CHARGE, &xfer); /* charge now on app1's cgroup */ close(cg_fd);
Signed-off-by: Albert Esteve aesteve@redhat.com --- drivers/dma-buf/dma-buf.c | 43 +++++++++++++++++++++++++++++++++++++ drivers/dma-buf/heaps/system_heap.c | 1 + include/linux/dma-buf.h | 5 +++++ include/linux/memcontrol.h | 9 ++++++++ include/uapi/linux/dma-buf.h | 26 ++++++++++++++++++++++ mm/memcontrol.c | 41 +++++++++++++++++++++++++++++++++++ 6 files changed, 125 insertions(+)
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index f31f49ebd0af..07513ecedc10 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -540,6 +540,45 @@ static long dma_buf_import_sync_file(struct dma_buf *dmabuf, } #endif
+/* Transfer a dma-buf's memcg charge; see struct dma_buf_transfer_charge */ +static long dma_buf_xfer_charge(struct dma_buf *dmabuf, + const void __user *user_data) +{ + struct dma_buf_transfer_charge arg; + struct mem_cgroup *memcg; + int ret = 0; + + if (copy_from_user(&arg, user_data, sizeof(arg))) + return -EFAULT; + + if (!IS_ENABLED(CONFIG_MEMCG)) + return 0; + + if (arg.flags != 0) + return -EINVAL; + + if (!dmabuf->memcg_account) + return -EOPNOTSUPP; + + memcg = mem_cgroup_get_from_fd(arg.charge_fd); + if (IS_ERR(memcg)) + return PTR_ERR(memcg); + + if (dmabuf->memcg == memcg) + goto skip_transfer; + + if (!mem_cgroup_transfer_dmabuf_charge(dmabuf, memcg)) { + ret = -ENOMEM; + goto skip_transfer; + } + + return 0; + +skip_transfer: + mem_cgroup_put(memcg); + return ret; +} + static long dma_buf_ioctl(struct file *file, unsigned int cmd, unsigned long arg) { @@ -590,6 +629,9 @@ static long dma_buf_ioctl(struct file *file, return dma_buf_import_sync_file(dmabuf, (const void __user *)arg); #endif
+ case DMA_BUF_IOCTL_XFER_CHARGE: + return dma_buf_xfer_charge(dmabuf, (const void __user *)arg); + default: return -ENOTTY; } @@ -750,6 +792,7 @@ struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info) dmabuf->size = exp_info->size; dmabuf->exp_name = exp_info->exp_name; dmabuf->owner = exp_info->owner; + dmabuf->memcg_account = exp_info->memcg_account; spin_lock_init(&dmabuf->name_lock); init_waitqueue_head(&dmabuf->poll); dmabuf->cb_in.poll = dmabuf->cb_out.poll = &dmabuf->poll; diff --git a/drivers/dma-buf/heaps/system_heap.c b/drivers/dma-buf/heaps/system_heap.c index adeea8cd328b..a764167167ba 100644 --- a/drivers/dma-buf/heaps/system_heap.c +++ b/drivers/dma-buf/heaps/system_heap.c @@ -479,6 +479,7 @@ static struct dma_buf *system_heap_allocate(struct dma_heap *heap, exp_info.size = buffer->len; exp_info.flags = fd_flags; exp_info.priv = buffer; + exp_info.memcg_account = true; dmabuf = dma_buf_export(&exp_info); if (IS_ERR(dmabuf)) { ret = PTR_ERR(dmabuf); diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h index 23ec0ff23fba..ac0ec88cab93 100644 --- a/include/linux/dma-buf.h +++ b/include/linux/dma-buf.h @@ -433,6 +433,9 @@ struct dma_buf {
/** @memcg: the cgroup to which this buffer is currently attributed */ struct mem_cgroup *memcg; + + /** @memcg_account: account buffer memory to cgroup */ + bool memcg_account; };
/** @@ -505,6 +508,7 @@ struct dma_buf_attachment { * @flags: mode flags for the file * @resv: reservation-object, NULL to allocate default one * @priv: Attach private data of allocator to this buffer + * @memcg_account: account buffer memory to cgroup * * This structure holds the information required to export the buffer. Used * with dma_buf_export() only. @@ -517,6 +521,7 @@ struct dma_buf_export_info { int flags; struct dma_resv *resv; void *priv; + bool memcg_account; };
/** diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 6b30baa79fa9..36fddafbef4e 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -679,6 +679,9 @@ bool mem_cgroup_reserve_dmabuf(struct mem_cgroup *memcg, gfp_t gfp, void mem_cgroup_commit_dmabuf(struct dma_buf *dmabuf, struct mem_cgroup *memcg, unsigned int nr_pages);
+bool mem_cgroup_transfer_dmabuf_charge(struct dma_buf *dmabuf, + struct mem_cgroup *new_memcg); + void __mem_cgroup_uncharge(struct folio *folio);
/** @@ -1206,6 +1209,12 @@ static inline void mem_cgroup_cancel_dmabuf(struct mem_cgroup *memcg, { }
+static inline bool mem_cgroup_transfer_dmabuf_charge(struct dma_buf *dmabuf, + struct mem_cgroup *new_memcg) +{ + return true; +} + static inline void mem_cgroup_uncharge(struct folio *folio) { } diff --git a/include/uapi/linux/dma-buf.h b/include/uapi/linux/dma-buf.h index e827c9d20c5d..ea957f4b1d38 100644 --- a/include/uapi/linux/dma-buf.h +++ b/include/uapi/linux/dma-buf.h @@ -168,6 +168,31 @@ struct dma_buf_import_sync_file { __s32 fd; };
+/** + * struct dma_buf_transfer_charge - Transfer a dma-buf's memcg charge + * + * Any holder of a dma-buf file descriptor can perform a + * DMA_BUF_IOCTL_XFER_CHARGE to attribute the buffer's memory + * cost to a specific cgroup, or move it from one cgroup to + * another. The ioctl charges the new cgroup before uncharging + * the old one atomically. On failure the original charge is + * preserved. If the buffer has no existing charge, a new + * charge is established. + */ +struct dma_buf_transfer_charge { + /** @flags: Reserved, must be zero */ + __u32 flags; /* unused for now */ + /** + * @charge_fd: File descriptor identifying the target cgroup. + * + * May be either a pidfd, in which case the charge moves to the + * memory cgroup of the referenced process, or a cgroupfd obtained + * by opening a cgroup v2 directory, in which case the charge moves + * directly to that cgroup's memory controller. + */ + __u32 charge_fd; +}; + #define DMA_BUF_BASE 'b' #define DMA_BUF_IOCTL_SYNC _IOW(DMA_BUF_BASE, 0, struct dma_buf_sync)
@@ -179,5 +204,6 @@ struct dma_buf_import_sync_file { #define DMA_BUF_SET_NAME_B _IOW(DMA_BUF_BASE, 1, __u64) #define DMA_BUF_IOCTL_EXPORT_SYNC_FILE _IOWR(DMA_BUF_BASE, 2, struct dma_buf_export_sync_file) #define DMA_BUF_IOCTL_IMPORT_SYNC_FILE _IOW(DMA_BUF_BASE, 3, struct dma_buf_import_sync_file) +#define DMA_BUF_IOCTL_XFER_CHARGE _IOW(DMA_BUF_BASE, 4, struct dma_buf_transfer_charge)
#endif diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 7b841b905759..3adc84fe6668 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -5786,6 +5786,47 @@ void mem_cgroup_cancel_dmabuf(struct mem_cgroup *memcg, unsigned int nr_pages) refill_stock(memcg, nr_pages); }
+/** + * mem_cgroup_transfer_dmabuf_charge - move a dma-buf charge + * @dmabuf: buffer to transfer charge + * @new_memcg: target memcg; caller must hold a reference + * + * Transfers the charge for @dmabuf to @new_memcg and, on + * success, stores @new_memcg in @dmabuf->memcg. + * Returns %true on success, %false if the charge against @new_memcg + * failed or a concurrent transfer raced on @dmabuf->memcg. + * On failure the caller retains its reference to @new_memcg. + */ +bool mem_cgroup_transfer_dmabuf_charge(struct dma_buf *dmabuf, + struct mem_cgroup *new_memcg) +{ + struct mem_cgroup *old_memcg = READ_ONCE(dmabuf->memcg); + unsigned int nr_pages = PAGE_ALIGN(dmabuf->size) >> PAGE_SHIFT; + + if (mem_cgroup_disabled()) + return true; + + if (!mem_cgroup_reserve_dmabuf(new_memcg, GFP_KERNEL, nr_pages)) + return false; + + mod_memcg_state(new_memcg, MEMCG_DMABUF, nr_pages); + + if (cmpxchg(&dmabuf->memcg, old_memcg, new_memcg) != old_memcg) { + mod_memcg_state(new_memcg, MEMCG_DMABUF, -nr_pages); + mem_cgroup_cancel_dmabuf(new_memcg, nr_pages); + return false; + } + + if (old_memcg) { + /* Uncharge old cgroup */ + mod_memcg_state(old_memcg, MEMCG_DMABUF, -nr_pages); + mem_cgroup_cancel_dmabuf(old_memcg, nr_pages); + mem_cgroup_put(old_memcg); + } + + return true; +} + /** * mem_cgroup_uncharge_dmabuf - uncharge a dma-buf from its memcg * @dmabuf: buffer to uncharge