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Message-ID: <20260116190517.3268458-1-tjmercier@google.com>
Date: Fri, 16 Jan 2026 11:05:12 -0800
From: "T.J. Mercier" <tjmercier@...gle.com>
To: Sumit Semwal <sumit.semwal@...aro.org>,
"Christian König" <christian.koenig@....com>, Jonathan Corbet <corbet@....net>
Cc: "T.J. Mercier" <tjmercier@...gle.com>, linux-kernel@...r.kernel.org,
linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
linaro-mm-sig@...ts.linaro.org, linux-doc@...r.kernel.org
Subject: [PATCH] dma-buf: Remove DMA-BUF sysfs stats
Commit bdb8d06dfefd ("dmabuf: Add the capability to expose DMA-BUF stats
in sysfs") added dmabuf statistics to sysfs in 2021 under
CONFIG_DMABUF_SYSFS_STATS. After being used in production, performance
problems were discovered leading to its deprecation in 2022 in commit
e0a9f1fe206a ("dma-buf: deprecate DMABUF_SYSFS_STATS"). Some of the
problems with this interface were discussed in my LPC 2025 talk. [1][2]
Android was probably the last user of the interface, which has since
been migrated to use the dmabuf BPF iterator [3] to obtain the same
information more cheaply. As promised in that series, now that the
longterm stable 6.18 kernel has been released let's remove the sysfs
dmabuf statistics from the kernel.
[1] https://www.youtube.com/watch?v=D83qygudq9c
[2] https://lpc.events/event/19/contributions/2118/
[3] https://lore.kernel.org/all/20250522230429.941193-1-tjmercier@google.com/
Signed-off-by: T.J. Mercier <tjmercier@...gle.com>
---
.../ABI/testing/sysfs-kernel-dmabuf-buffers | 24 ---
Documentation/driver-api/dma-buf.rst | 5 -
drivers/dma-buf/Kconfig | 15 --
drivers/dma-buf/Makefile | 1 -
drivers/dma-buf/dma-buf-sysfs-stats.c | 202 ------------------
drivers/dma-buf/dma-buf-sysfs-stats.h | 35 ---
drivers/dma-buf/dma-buf.c | 18 --
include/linux/dma-buf.h | 12 --
8 files changed, 312 deletions(-)
delete mode 100644 Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers
delete mode 100644 drivers/dma-buf/dma-buf-sysfs-stats.c
delete mode 100644 drivers/dma-buf/dma-buf-sysfs-stats.h
diff --git a/Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers b/Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers
deleted file mode 100644
index 5d3bc997dc64..000000000000
--- a/Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers
+++ /dev/null
@@ -1,24 +0,0 @@
-What: /sys/kernel/dmabuf/buffers
-Date: May 2021
-KernelVersion: v5.13
-Contact: Hridya Valsaraju <hridya@...gle.com>
-Description: The /sys/kernel/dmabuf/buffers directory contains a
- snapshot of the internal state of every DMA-BUF.
- /sys/kernel/dmabuf/buffers/<inode_number> will contain the
- statistics for the DMA-BUF with the unique inode number
- <inode_number>
-Users: kernel memory tuning/debugging tools
-
-What: /sys/kernel/dmabuf/buffers/<inode_number>/exporter_name
-Date: May 2021
-KernelVersion: v5.13
-Contact: Hridya Valsaraju <hridya@...gle.com>
-Description: This file is read-only and contains the name of the exporter of
- the DMA-BUF.
-
-What: /sys/kernel/dmabuf/buffers/<inode_number>/size
-Date: May 2021
-KernelVersion: v5.13
-Contact: Hridya Valsaraju <hridya@...gle.com>
-Description: This file is read-only and specifies the size of the DMA-BUF in
- bytes.
diff --git a/Documentation/driver-api/dma-buf.rst b/Documentation/driver-api/dma-buf.rst
index 29abf1eebf9f..2f36c21d9948 100644
--- a/Documentation/driver-api/dma-buf.rst
+++ b/Documentation/driver-api/dma-buf.rst
@@ -125,11 +125,6 @@ Implicit Fence Poll Support
.. kernel-doc:: drivers/dma-buf/dma-buf.c
:doc: implicit fence polling
-DMA-BUF statistics
-~~~~~~~~~~~~~~~~~~
-.. kernel-doc:: drivers/dma-buf/dma-buf-sysfs-stats.c
- :doc: overview
-
DMA Buffer ioctls
~~~~~~~~~~~~~~~~~
diff --git a/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig
index fdd823e446cc..012d22e941d6 100644
--- a/drivers/dma-buf/Kconfig
+++ b/drivers/dma-buf/Kconfig
@@ -75,21 +75,6 @@ menuconfig DMABUF_HEAPS
allows userspace to allocate dma-bufs that can be shared
between drivers.
-menuconfig DMABUF_SYSFS_STATS
- bool "DMA-BUF sysfs statistics (DEPRECATED)"
- depends on DMA_SHARED_BUFFER
- help
- Choose this option to enable DMA-BUF sysfs statistics
- in location /sys/kernel/dmabuf/buffers.
-
- /sys/kernel/dmabuf/buffers/<inode_number> will contain
- statistics for the DMA-BUF with the unique inode number
- <inode_number>.
-
- This option is deprecated and should sooner or later be removed.
- Android is the only user of this and it turned out that this resulted
- in quite some performance problems.
-
source "drivers/dma-buf/heaps/Kconfig"
endmenu
diff --git a/drivers/dma-buf/Makefile b/drivers/dma-buf/Makefile
index 2008fb7481b3..7a85565d906b 100644
--- a/drivers/dma-buf/Makefile
+++ b/drivers/dma-buf/Makefile
@@ -6,7 +6,6 @@ obj-$(CONFIG_DMABUF_HEAPS) += heaps/
obj-$(CONFIG_SYNC_FILE) += sync_file.o
obj-$(CONFIG_SW_SYNC) += sw_sync.o sync_debug.o
obj-$(CONFIG_UDMABUF) += udmabuf.o
-obj-$(CONFIG_DMABUF_SYSFS_STATS) += dma-buf-sysfs-stats.o
dmabuf_selftests-y := \
selftest.o \
diff --git a/drivers/dma-buf/dma-buf-sysfs-stats.c b/drivers/dma-buf/dma-buf-sysfs-stats.c
deleted file mode 100644
index b5b62e40ccc1..000000000000
--- a/drivers/dma-buf/dma-buf-sysfs-stats.c
+++ /dev/null
@@ -1,202 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0-only
-/*
- * DMA-BUF sysfs statistics.
- *
- * Copyright (C) 2021 Google LLC.
- */
-
-#include <linux/dma-buf.h>
-#include <linux/dma-resv.h>
-#include <linux/kobject.h>
-#include <linux/printk.h>
-#include <linux/slab.h>
-#include <linux/sysfs.h>
-
-#include "dma-buf-sysfs-stats.h"
-
-#define to_dma_buf_entry_from_kobj(x) container_of(x, struct dma_buf_sysfs_entry, kobj)
-
-/**
- * DOC: overview
- *
- * ``/sys/kernel/debug/dma_buf/bufinfo`` provides an overview of every DMA-BUF
- * in the system. However, since debugfs is not safe to be mounted in
- * production, procfs and sysfs can be used to gather DMA-BUF statistics on
- * production systems.
- *
- * The ``/proc/<pid>/fdinfo/<fd>`` files in procfs can be used to gather
- * information about DMA-BUF fds. Detailed documentation about the interface
- * is present in Documentation/filesystems/proc.rst.
- *
- * Unfortunately, the existing procfs interfaces can only provide information
- * about the DMA-BUFs for which processes hold fds or have the buffers mmapped
- * into their address space. This necessitated the creation of the DMA-BUF sysfs
- * statistics interface to provide per-buffer information on production systems.
- *
- * The interface at ``/sys/kernel/dmabuf/buffers`` exposes information about
- * every DMA-BUF when ``CONFIG_DMABUF_SYSFS_STATS`` is enabled.
- *
- * The following stats are exposed by the interface:
- *
- * * ``/sys/kernel/dmabuf/buffers/<inode_number>/exporter_name``
- * * ``/sys/kernel/dmabuf/buffers/<inode_number>/size``
- *
- * The information in the interface can also be used to derive per-exporter
- * statistics. The data from the interface can be gathered on error conditions
- * or other important events to provide a snapshot of DMA-BUF usage.
- * It can also be collected periodically by telemetry to monitor various metrics.
- *
- * Detailed documentation about the interface is present in
- * Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers.
- */
-
-struct dma_buf_stats_attribute {
- struct attribute attr;
- ssize_t (*show)(struct dma_buf *dmabuf,
- struct dma_buf_stats_attribute *attr, char *buf);
-};
-#define to_dma_buf_stats_attr(x) container_of(x, struct dma_buf_stats_attribute, attr)
-
-static ssize_t dma_buf_stats_attribute_show(struct kobject *kobj,
- struct attribute *attr,
- char *buf)
-{
- struct dma_buf_stats_attribute *attribute;
- struct dma_buf_sysfs_entry *sysfs_entry;
- struct dma_buf *dmabuf;
-
- attribute = to_dma_buf_stats_attr(attr);
- sysfs_entry = to_dma_buf_entry_from_kobj(kobj);
- dmabuf = sysfs_entry->dmabuf;
-
- if (!dmabuf || !attribute->show)
- return -EIO;
-
- return attribute->show(dmabuf, attribute, buf);
-}
-
-static const struct sysfs_ops dma_buf_stats_sysfs_ops = {
- .show = dma_buf_stats_attribute_show,
-};
-
-static ssize_t exporter_name_show(struct dma_buf *dmabuf,
- struct dma_buf_stats_attribute *attr,
- char *buf)
-{
- return sysfs_emit(buf, "%s\n", dmabuf->exp_name);
-}
-
-static ssize_t size_show(struct dma_buf *dmabuf,
- struct dma_buf_stats_attribute *attr,
- char *buf)
-{
- return sysfs_emit(buf, "%zu\n", dmabuf->size);
-}
-
-static struct dma_buf_stats_attribute exporter_name_attribute =
- __ATTR_RO(exporter_name);
-static struct dma_buf_stats_attribute size_attribute = __ATTR_RO(size);
-
-static struct attribute *dma_buf_stats_default_attrs[] = {
- &exporter_name_attribute.attr,
- &size_attribute.attr,
- NULL,
-};
-ATTRIBUTE_GROUPS(dma_buf_stats_default);
-
-static void dma_buf_sysfs_release(struct kobject *kobj)
-{
- struct dma_buf_sysfs_entry *sysfs_entry;
-
- sysfs_entry = to_dma_buf_entry_from_kobj(kobj);
- kfree(sysfs_entry);
-}
-
-static const struct kobj_type dma_buf_ktype = {
- .sysfs_ops = &dma_buf_stats_sysfs_ops,
- .release = dma_buf_sysfs_release,
- .default_groups = dma_buf_stats_default_groups,
-};
-
-void dma_buf_stats_teardown(struct dma_buf *dmabuf)
-{
- struct dma_buf_sysfs_entry *sysfs_entry;
-
- sysfs_entry = dmabuf->sysfs_entry;
- if (!sysfs_entry)
- return;
-
- kobject_del(&sysfs_entry->kobj);
- kobject_put(&sysfs_entry->kobj);
-}
-
-
-/* Statistics files do not need to send uevents. */
-static int dmabuf_sysfs_uevent_filter(const struct kobject *kobj)
-{
- return 0;
-}
-
-static const struct kset_uevent_ops dmabuf_sysfs_no_uevent_ops = {
- .filter = dmabuf_sysfs_uevent_filter,
-};
-
-static struct kset *dma_buf_stats_kset;
-static struct kset *dma_buf_per_buffer_stats_kset;
-int dma_buf_init_sysfs_statistics(void)
-{
- dma_buf_stats_kset = kset_create_and_add("dmabuf",
- &dmabuf_sysfs_no_uevent_ops,
- kernel_kobj);
- if (!dma_buf_stats_kset)
- return -ENOMEM;
-
- dma_buf_per_buffer_stats_kset = kset_create_and_add("buffers",
- &dmabuf_sysfs_no_uevent_ops,
- &dma_buf_stats_kset->kobj);
- if (!dma_buf_per_buffer_stats_kset) {
- kset_unregister(dma_buf_stats_kset);
- return -ENOMEM;
- }
-
- return 0;
-}
-
-void dma_buf_uninit_sysfs_statistics(void)
-{
- kset_unregister(dma_buf_per_buffer_stats_kset);
- kset_unregister(dma_buf_stats_kset);
-}
-
-int dma_buf_stats_setup(struct dma_buf *dmabuf, struct file *file)
-{
- struct dma_buf_sysfs_entry *sysfs_entry;
- int ret;
-
- if (!dmabuf->exp_name) {
- pr_err("exporter name must not be empty if stats needed\n");
- return -EINVAL;
- }
-
- sysfs_entry = kzalloc(sizeof(struct dma_buf_sysfs_entry), GFP_KERNEL);
- if (!sysfs_entry)
- return -ENOMEM;
-
- sysfs_entry->kobj.kset = dma_buf_per_buffer_stats_kset;
- sysfs_entry->dmabuf = dmabuf;
-
- dmabuf->sysfs_entry = sysfs_entry;
-
- /* create the directory for buffer stats */
- ret = kobject_init_and_add(&sysfs_entry->kobj, &dma_buf_ktype, NULL,
- "%lu", file_inode(file)->i_ino);
- if (ret)
- goto err_sysfs_dmabuf;
-
- return 0;
-
-err_sysfs_dmabuf:
- kobject_put(&sysfs_entry->kobj);
- dmabuf->sysfs_entry = NULL;
- return ret;
-}
diff --git a/drivers/dma-buf/dma-buf-sysfs-stats.h b/drivers/dma-buf/dma-buf-sysfs-stats.h
deleted file mode 100644
index 7a8a995b75ba..000000000000
--- a/drivers/dma-buf/dma-buf-sysfs-stats.h
+++ /dev/null
@@ -1,35 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0-only */
-/*
- * DMA-BUF sysfs statistics.
- *
- * Copyright (C) 2021 Google LLC.
- */
-
-#ifndef _DMA_BUF_SYSFS_STATS_H
-#define _DMA_BUF_SYSFS_STATS_H
-
-#ifdef CONFIG_DMABUF_SYSFS_STATS
-
-int dma_buf_init_sysfs_statistics(void);
-void dma_buf_uninit_sysfs_statistics(void);
-
-int dma_buf_stats_setup(struct dma_buf *dmabuf, struct file *file);
-
-void dma_buf_stats_teardown(struct dma_buf *dmabuf);
-#else
-
-static inline int dma_buf_init_sysfs_statistics(void)
-{
- return 0;
-}
-
-static inline void dma_buf_uninit_sysfs_statistics(void) {}
-
-static inline int dma_buf_stats_setup(struct dma_buf *dmabuf, struct file *file)
-{
- return 0;
-}
-
-static inline void dma_buf_stats_teardown(struct dma_buf *dmabuf) {}
-#endif
-#endif // _DMA_BUF_SYSFS_STATS_H
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index a4d8f2ff94e4..8e23580f1754 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -33,8 +33,6 @@
#include <uapi/linux/dma-buf.h>
#include <uapi/linux/magic.h>
-#include "dma-buf-sysfs-stats.h"
-
#define CREATE_TRACE_POINTS
#include <trace/events/dma_buf.h>
@@ -184,7 +182,6 @@ static void dma_buf_release(struct dentry *dentry)
*/
BUG_ON(dmabuf->cb_in.active || dmabuf->cb_out.active);
- dma_buf_stats_teardown(dmabuf);
dmabuf->ops->release(dmabuf);
if (dmabuf->resv == (struct dma_resv *)&dmabuf[1])
@@ -765,10 +762,6 @@ struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info)
dmabuf->resv = resv;
}
- ret = dma_buf_stats_setup(dmabuf, file);
- if (ret)
- goto err_dmabuf;
-
file->private_data = dmabuf;
file->f_path.dentry->d_fsdata = dmabuf;
dmabuf->file = file;
@@ -779,10 +772,6 @@ struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info)
return dmabuf;
-err_dmabuf:
- if (!resv)
- dma_resv_fini(dmabuf->resv);
- kfree(dmabuf);
err_file:
fput(file);
err_module:
@@ -1802,12 +1791,6 @@ static inline void dma_buf_uninit_debugfs(void)
static int __init dma_buf_init(void)
{
- int ret;
-
- ret = dma_buf_init_sysfs_statistics();
- if (ret)
- return ret;
-
dma_buf_mnt = kern_mount(&dma_buf_fs_type);
if (IS_ERR(dma_buf_mnt))
return PTR_ERR(dma_buf_mnt);
@@ -1821,6 +1804,5 @@ static void __exit dma_buf_deinit(void)
{
dma_buf_uninit_debugfs();
kern_unmount(dma_buf_mnt);
- dma_buf_uninit_sysfs_statistics();
}
__exitcall(dma_buf_deinit);
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index 0bc492090237..91f4939db89b 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -429,18 +429,6 @@ struct dma_buf {
__poll_t active;
} cb_in, cb_out;
-#ifdef CONFIG_DMABUF_SYSFS_STATS
- /**
- * @sysfs_entry:
- *
- * For exposing information about this buffer in sysfs. See also
- * `DMA-BUF statistics`_ for the uapi this enables.
- */
- struct dma_buf_sysfs_entry {
- struct kobject kobj;
- struct dma_buf *dmabuf;
- } *sysfs_entry;
-#endif
};
/**
base-commit: 26b4309a3ab82a0697751cde52eb336c29c19035
--
2.52.0.457.g6b5491de43-goog
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