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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 > --- > 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)) Please move the calculation of nr_pages after taking the dma_resv_lock(). We currently don't have anybody dynamically changing DMA-buf sizes but just to be on the save side. With that done Reviewed-by: Christian König Regards, Christian. > + 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 >