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. Concurrent transfers are serialized by the dma-buf reservation lock, so lockdep covers the locking order of the charge path early. The transfer implementation is generic (mem_cgroup_transfer_charge) and not dma-buf specific, so it can be reused by other subsystems.
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. The xfer ioctl returns -EOPNOTSUPP for buffers whose memcg is not set. Exporters opt in by passing a memcg through dma_buf_export_info at export time. 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 | 42 ++++++++++++++++++++++++++++++++++++++++++ include/linux/dma-buf.h | 3 ++- include/linux/memcontrol.h | 13 +++++++++++++ include/uapi/linux/dma-buf.h | 26 ++++++++++++++++++++++++++ mm/memcontrol.c | 42 ++++++++++++++++++++++++++++++++++++++++++ 5 files changed, 125 insertions(+), 1 deletion(-)
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index 837666273550..3bd26fbb1109 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; + unsigned int nr_pages = PAGE_ALIGN(dmabuf->size) >> PAGE_SHIFT; + 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; + + memcg = mem_cgroup_get_from_fd(arg.charge_fd); + if (IS_ERR(memcg)) + return PTR_ERR(memcg); + + dma_resv_lock(dmabuf->resv, NULL); + + if (!dmabuf->memcg) { + ret = -EOPNOTSUPP; + goto out; + } + + if (dmabuf->memcg != memcg && + !mem_cgroup_transfer_charge(&dmabuf->memcg, memcg, MEMCG_DMABUF, nr_pages)) + ret = -ENOMEM; + +out: + dma_resv_unlock(dmabuf->resv); + 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; } diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h index 85dd747c9b36..b01149d26b44 100644 --- a/include/linux/dma-buf.h +++ b/include/linux/dma-buf.h @@ -507,7 +507,8 @@ struct dma_buf_attachment { * @priv: Attach private data of allocator to this buffer * @memcg: memcg to charge for this buffer's memory. Set only for * buffers backed by system memory where @size reflects the - * actual allocation in bytes. + * actual allocation in bytes. Enables charge transfer via + * DMA_BUF_IOCTL_XFER_CHARGE. * * This structure holds the information required to export the buffer. Used * with dma_buf_export() only. diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index f8ec751b7d7b..af02d9777fe9 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -676,6 +676,11 @@ struct mem_cgroup *mem_cgroup_get_from_fd(int fd); bool mem_cgroup_reserve_dmabuf(struct mem_cgroup *memcg, gfp_t gfp, unsigned int nr_pages);
+bool mem_cgroup_transfer_charge(struct mem_cgroup **ptr_memcg, + struct mem_cgroup *new_memcg, + enum memcg_stat_item item, + unsigned int nr_pages); + void __mem_cgroup_uncharge(struct folio *folio);
/** @@ -1197,6 +1202,14 @@ static inline void mem_cgroup_cancel_dmabuf(struct mem_cgroup *memcg, { }
+static inline bool mem_cgroup_transfer_charge(struct mem_cgroup **ptr_memcg, + struct mem_cgroup *new_memcg, + enum memcg_stat_item item, + unsigned int nr_pages) +{ + 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..0aaf2e7d593b 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 memcg charge, the + * ioctl returns -EOPNOTSUPP. + */ +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 17fdefc56b97..3e717b5663c8 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -5752,6 +5752,48 @@ void mem_cgroup_cancel_dmabuf(struct mem_cgroup *memcg, unsigned int nr_pages) } EXPORT_SYMBOL_GPL(mem_cgroup_cancel_dmabuf);
+/** + * mem_cgroup_transfer_charge - move a charge between memcgs + * @ptr_memcg: pointer to the memcg to transfer from + * @new_memcg: target memcg; caller must hold a reference + * @item: stat counter to adjust + * @nr_pages: number of pages to transfer + * + * Transfers @nr_pages of charge from *@ptr_memcg to @new_memcg and, on + * success, stores @new_memcg in *@ptr_memcg. + * + * Updates to *@ptr_memcg must be serialized by the caller. + * Returns %true on success, %false if the charge against @new_memcg + * failed. + */ +bool mem_cgroup_transfer_charge(struct mem_cgroup **ptr_memcg, + struct mem_cgroup *new_memcg, + enum memcg_stat_item item, + unsigned int nr_pages) +{ + struct mem_cgroup *old_memcg = *ptr_memcg; + + if (!new_memcg || mem_cgroup_disabled()) + return true; + + if (try_charge(new_memcg, GFP_KERNEL, nr_pages)) + return false; + + mod_memcg_state(new_memcg, item, nr_pages); + css_get(&new_memcg->css); + *ptr_memcg = new_memcg; + + if (old_memcg) { + /* Uncharge old cgroup */ + mod_memcg_state(old_memcg, item, -nr_pages); + if (!mem_cgroup_is_root(old_memcg)) + refill_stock(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