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 <[email protected]>
---
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
--
2.55.0
