[PATCH 2/3] sysctl: add support for drop_caches for individual filesystem

[Ye Bin <yebin@huaweicloud.com>]

From: Ye Bin <yebin10@huawei.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@huawei.com>
---
 fs/drop_caches.c   | 43 +++++++++++++++++++++++++++++++++++++++++++
 include/linux/mm.h |  2 ++
 kernel/sysctl.c    |  9 +++++++++
 3 files changed, 54 insertions(+)

diff --git a/fs/drop_caches.c b/fs/drop_caches.c
index d45ef541d848..99d412cf3e52 100644
--- a/fs/drop_caches.c
+++ b/fs/drop_caches.c
@@ -77,3 +77,46 @@ int drop_caches_sysctl_handler(const struct ctl_table *table, int write,
 	}
 	return 0;
 }
+
+int drop_fs_caches_sysctl_handler(const struct ctl_table *table, int write,
+				  void *buffer, size_t *length, loff_t *ppos)
+{
+	unsigned int major, minor;
+	unsigned int ctl;
+	struct super_block *sb;
+	static int stfu;
+
+	if (!write)
+		return 0;
+
+	if (sscanf(buffer, "%u:%u:%u", &major, &minor, &ctl) != 3)
+		return -EINVAL;
+
+	if (ctl < *((int *)table->extra1) || ctl > *((int *)table->extra2))
+		return -EINVAL;
+
+	sb = user_get_super(MKDEV(major, minor), false);
+	if (!sb)
+		return -EINVAL;
+
+	if (ctl & 1) {
+		lru_add_drain_all();
+		drop_pagecache_sb(sb, NULL);
+		count_vm_event(DROP_PAGECACHE);
+	}
+
+	if (ctl & 2) {
+		shrink_dcache_sb(sb);
+		shrink_icache_sb(sb);
+		count_vm_event(DROP_SLAB);
+	}
+
+	drop_super(sb);
+
+	if (!stfu)
+		pr_info("%s (%d): drop_fs_caches: %u:%u:%d\n", current->comm,
+			task_pid_nr(current), major, minor, ctl);
+	stfu |= ctl & 4;
+
+	return 0;
+}
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 344541f8cba0..43079478296f 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3788,6 +3788,8 @@ extern bool process_shares_mm(struct task_struct *p, struct mm_struct *mm);
 extern int sysctl_drop_caches;
 int drop_caches_sysctl_handler(const struct ctl_table *, int, void *, size_t *,
 		loff_t *);
+int drop_fs_caches_sysctl_handler(const struct ctl_table *table, int write,
+				  void *buffer, size_t *length, loff_t *ppos);
 #endif
 
 void drop_slab(void);
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 79e6cb1d5c48..d434cbe10e47 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -2101,6 +2101,15 @@ static struct ctl_table vm_table[] = {
 		.extra1		= SYSCTL_ONE,
 		.extra2		= SYSCTL_FOUR,
 	},
+	{
+		.procname	= "drop_fs_caches",
+		.data		= NULL,
+		.maxlen		= 256,
+		.mode		= 0200,
+		.proc_handler	= drop_fs_caches_sysctl_handler,
+		.extra1         = SYSCTL_ONE,
+		.extra2         = SYSCTL_FOUR,
+	},
 	{
 		.procname	= "page_lock_unfairness",
 		.data		= &sysctl_page_lock_unfairness,
-- 
2.31.1