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Message-Id: <20251117112735.4170831-3-yebin@huaweicloud.com>
Date: Mon, 17 Nov 2025 19:27:34 +0800
From: Ye Bin <yebin@...weicloud.com>
To: viro@...iv.linux.org.uk,
brauner@...nel.org,
jack@...e.cz,
linux-fsdevel@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
yebin10@...wei.com
Subject: [PATCH v2 2/3] sysctl: add support for drop_caches for individual filesystem
From: Ye Bin <yebin10@...wei.com>
In order to better analyze the issue of file system uninstallation caused
by kernel module opening files, it is necessary to perform dentry recycling
on a single file system. But now, apart from global dentry recycling, it is
not supported to do dentry recycling on a single file system separately.
This feature has usage scenarios in problem localization scenarios.At the
same time, it also provides users with a slightly fine-grained
pagecache/entry recycling mechanism.
This patch supports the recycling of pagecache/entry for individual file
systems.
Signed-off-by: Ye Bin <yebin10@...wei.com>
---
fs/drop_caches.c | 127 +++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 127 insertions(+)
diff --git a/fs/drop_caches.c b/fs/drop_caches.c
index 49f56a598ecb..3c7e624129ec 100644
--- a/fs/drop_caches.c
+++ b/fs/drop_caches.c
@@ -11,6 +11,10 @@
#include <linux/sysctl.h>
#include <linux/gfp.h>
#include <linux/swap.h>
+#include <linux/ptrace.h>
+#include <asm/syscall.h>
+#include <linux/task_work.h>
+#include <linux/namei.h>
#include "internal.h"
/* A global variable is a bit ugly, but it keeps the code simple */
@@ -78,6 +82,124 @@ static int drop_caches_sysctl_handler(const struct ctl_table *table, int write,
return 0;
}
+struct drop_fs_caches_work {
+ struct callback_head task_work;
+ dev_t dev;
+ char *path;
+ unsigned int ctl;
+};
+
+static void drop_fs_caches(struct callback_head *twork)
+{
+ int ret;
+ struct super_block *sb;
+ static bool suppress;
+ struct drop_fs_caches_work *work = container_of(twork,
+ struct drop_fs_caches_work, task_work);
+ unsigned int ctl = work->ctl;
+ dev_t dev = work->dev;
+
+ if (work->path) {
+ struct path path;
+
+ ret = kern_path(work->path, LOOKUP_FOLLOW, &path);
+ if (ret) {
+ syscall_set_return_value(current,
+ current_pt_regs(),
+ 0, ret);
+ goto out;
+ }
+ dev = path.dentry->d_sb->s_dev;
+ /* Make this file's dentry and inode recyclable */
+ path_put(&path);
+ }
+
+ sb = user_get_super(dev, false);
+ if (!sb) {
+ syscall_set_return_value(current, current_pt_regs(), 0,
+ -EINVAL);
+ goto out;
+ }
+
+ if (ctl & BIT(0)) {
+ lru_add_drain_all();
+ drop_pagecache_sb(sb, NULL);
+ count_vm_event(DROP_PAGECACHE);
+ }
+
+ if (ctl & BIT(1)) {
+ reclaim_dcache_sb(sb);
+ reclaim_icache_sb(sb);
+ count_vm_event(DROP_SLAB);
+ }
+
+ if (!READ_ONCE(suppress)) {
+ pr_info("%s (%d): %s: %d %u:%u\n", current->comm,
+ task_pid_nr(current), __func__, ctl,
+ MAJOR(sb->s_dev), MINOR(sb->s_dev));
+
+ if (ctl & BIT(2))
+ WRITE_ONCE(suppress, true);
+ }
+
+ drop_super(sb);
+out:
+ kfree(work->path);
+ kfree(work);
+}
+
+static int drop_fs_caches_sysctl_handler(const struct ctl_table *table,
+ int write, void *buffer,
+ size_t *length, loff_t *ppos)
+{
+ struct drop_fs_caches_work *work = NULL;
+ unsigned int major, minor;
+ unsigned int ctl;
+ int ret;
+ char *path = NULL;
+
+ if (!write)
+ return 0;
+
+ if (sscanf(buffer, "%u %u:%u", &ctl, &major, &minor) != 3) {
+ path = kstrdup(buffer, GFP_NOFS);
+ if (!path) {
+ ret = -ENOMEM;
+ goto out;
+ }
+
+ if (sscanf(buffer, "%u %s", &ctl, path) != 2) {
+ ret = -EINVAL;
+ goto out;
+ }
+ }
+
+ if (ctl < 1 || ctl > 7) {
+ ret = -EINVAL;
+ goto out;
+ }
+
+ work = kzalloc(sizeof(*work), GFP_KERNEL);
+ if (!work) {
+ ret = -ENOMEM;
+ goto out;
+ }
+
+ init_task_work(&work->task_work, drop_fs_caches);
+ if (!path)
+ work->dev = MKDEV(major, minor);
+ work->path = path;
+ work->ctl = ctl;
+ ret = task_work_add(current, &work->task_work, TWA_RESUME);
+out:
+ if (ret) {
+ kfree(path);
+ kfree(work);
+ }
+
+ return ret;
+}
+
static const struct ctl_table drop_caches_table[] = {
{
.procname = "drop_caches",
@@ -88,6 +210,11 @@ static const struct ctl_table drop_caches_table[] = {
.extra1 = SYSCTL_ONE,
.extra2 = SYSCTL_FOUR,
},
+ {
+ .procname = "drop_fs_caches",
+ .mode = 0200,
+ .proc_handler = drop_fs_caches_sysctl_handler,
+ },
};
static int __init init_vm_drop_caches_sysctls(void)
--
2.34.1
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