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Subject[PATCH 09/14] FS-Cache: Avoid ENFILE checking for kernel-specific open files [try #8]
Date
Make it possible to avoid ENFILE checking for kernel specific open files, such
as are used by the CacheFiles module.

After, for example, tarring up a kernel source tree over the network, the
CacheFiles module may easily have 20000+ files open in the backing filesystem,
thus causing all non-root processes to be given error ENFILE when they try to
open a file, socket, pipe, etc..
Signed-Off-By: David Howells <dhowells@redhat.com>
---
Documentation/sysctl/fs.txt | 6 ++++-
fs/file_table.c | 48 +++++++++++++++++++++++++++++++++++--------
fs/open.c | 20 ++++++++++++++++++
include/linux/file.h | 1 -
include/linux/fs.h | 10 +++++++++
include/linux/sysctl.h | 1 +
kernel/sysctl.c | 11 ++++++++++
7 files changed, 86 insertions(+), 11 deletions(-)
diff --git a/Documentation/sysctl/fs.txt b/Documentation/sysctl/fs.txt
index 0b62c62..ead15f0 100644
--- a/Documentation/sysctl/fs.txt
+++ b/Documentation/sysctl/fs.txt
@@ -71,7 +71,7 @@ you might want to raise the limit.

==============================================================

-file-max & file-nr:
+file-max, file-nr & file-kernel:

The kernel allocates file handles dynamically, but as yet it
doesn't free them again.
@@ -88,6 +88,10 @@ close to the maximum, but the number of
significantly greater than 0, you've encountered a peak in your
usage of file handles and you don't need to increase the maximum.

+The value in file-kernel denotes the number of internal file handles
+that the kernel has open. These do not contribute to ENFILE
+accounting.
+
==============================================================

inode-max, inode-nr & inode-state:
diff --git a/fs/file_table.c b/fs/file_table.c
index bcea199..0b42be9 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -30,10 +30,13 @@ struct files_stat_struct files_stat = {
.max_files = NR_FILE
};

+struct files_kernel_stat_struct files_kernel_stat;
+
/* public. Not pretty! */
__cacheline_aligned_in_smp DEFINE_SPINLOCK(files_lock);

static struct percpu_counter nr_files __cacheline_aligned_in_smp;
+static atomic_t nr_kernel_files;

static inline void file_free_rcu(struct rcu_head *head)
{
@@ -43,7 +46,10 @@ static inline void file_free_rcu(struct

static inline void file_free(struct file *f)
{
- percpu_counter_dec(&nr_files);
+ if (f->f_kernel_flags & FKFLAGS_NO_ENFILE)
+ atomic_dec(&nr_kernel_files);
+ else
+ percpu_counter_dec(&nr_files);
call_rcu(&f->f_u.fu_rcuhead, file_free_rcu);
}

@@ -74,45 +80,64 @@ int proc_nr_files(ctl_table *table, int
files_stat.nr_files = get_nr_files();
return proc_dointvec(table, write, filp, buffer, lenp, ppos);
}
+int proc_files_kernel(ctl_table *table, int write, struct file *filp,
+ void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+ files_kernel_stat.nr_kernel_files = atomic_read(&nr_kernel_files);
+ return proc_dointvec(table, write, filp, buffer, lenp, ppos);
+}
#else
int proc_nr_files(ctl_table *table, int write, struct file *filp,
void __user *buffer, size_t *lenp, loff_t *ppos)
{
return -ENOSYS;
}
+int proc_files_kernel(ctl_table *table, int write, struct file *filp,
+ void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+ return -ENOSYS;
+}
#endif

/* Find an unused file structure and return a pointer to it.
* Returns NULL, if there are no more free file structures or
* we run out of memory.
*/
-struct file *get_empty_filp(void)
+struct file *get_empty_kernel_filp(unsigned short kflags)
{
struct task_struct *tsk;
static int old_max;
struct file * f;

/*
- * Privileged users can go above max_files
+ * Privileged users can go above max_files and internal kernel users
+ * can avoid it completely
*/
- if (get_nr_files() >= files_stat.max_files && !capable(CAP_SYS_ADMIN)) {
+ if (!(kflags & FKFLAGS_NO_ENFILE) &&
+ get_nr_files() >= files_stat.max_files &&
+ !capable(CAP_SYS_ADMIN)
+ ) {
/*
- * percpu_counters are inaccurate. Do an expensive check before
- * we go and fail.
+ * percpu_counters are inaccurate. Do an expensive
+ * check before we go and fail.
*/
if (percpu_counter_sum(&nr_files) >= files_stat.max_files)
goto over;
}

- f = kmem_cache_alloc(filp_cachep, GFP_KERNEL);
+ f = kmem_cache_zalloc(filp_cachep, GFP_KERNEL);
if (f == NULL)
goto fail;

- percpu_counter_inc(&nr_files);
- memset(f, 0, sizeof(*f));
+ if (kflags & FKFLAGS_NO_ENFILE)
+ atomic_inc(&nr_kernel_files);
+ else
+ percpu_counter_inc(&nr_files);
+
if (security_file_alloc(f))
goto fail_sec;

+ f->f_kernel_flags = kflags;
tsk = current;
INIT_LIST_HEAD(&f->f_u.fu_list);
atomic_set(&f->f_count, 1);
@@ -138,6 +163,11 @@ fail:
return NULL;
}

+struct file *get_empty_filp(void)
+{
+ return get_empty_kernel_filp(0);
+}
+
EXPORT_SYMBOL(get_empty_filp);

void fastcall fput(struct file *file)
diff --git a/fs/open.c b/fs/open.c
index c7a48ee..a7d293f 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -974,6 +974,26 @@ struct file *dentry_open(struct dentry *
EXPORT_SYMBOL(dentry_open);

/*
+ * open a specifically in-kernel file
+ */
+struct file *dentry_open_kernel(struct dentry *dentry, struct vfsmount *mnt, int flags)
+{
+ int error;
+ struct file *f;
+
+ error = -ENFILE;
+ f = get_empty_kernel_filp(FKFLAGS_NO_ENFILE);
+ if (f == NULL) {
+ dput(dentry);
+ mntput(mnt);
+ return ERR_PTR(error);
+ }
+
+ return __dentry_open(dentry, mnt, flags, f, NULL);
+}
+EXPORT_SYMBOL_GPL(dentry_open_kernel);
+
+/*
* Find an empty file descriptor entry, and mark it busy.
*/
int get_unused_fd(void)
diff --git a/include/linux/file.h b/include/linux/file.h
index 9f7c251..da7be8f 100644
--- a/include/linux/file.h
+++ b/include/linux/file.h
@@ -79,7 +79,6 @@ extern void FASTCALL(set_close_on_exec(u
extern void put_filp(struct file *);
extern int get_unused_fd(void);
extern void FASTCALL(put_unused_fd(unsigned int fd));
-struct kmem_cache;

extern struct file ** alloc_fd_array(int);
extern void free_fd_array(struct file **, int);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index e57518e..cdb0972 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -34,7 +34,11 @@ struct files_stat_struct {
int nr_free_files; /* read only */
int max_files; /* tunable */
};
+struct files_kernel_stat_struct {
+ int nr_kernel_files; /* read only */
+};
extern struct files_stat_struct files_stat;
+extern struct files_kernel_stat_struct files_kernel_stat;
extern int get_max_files(void);

struct inodes_stat_t {
@@ -70,6 +74,8 @@ #define FMODE_PWRITE FMODE_PREAD /* Thes
behavior for cross-node execution/opening_for_writing of files */
#define FMODE_EXEC 16

+#define FKFLAGS_NO_ENFILE 1 /* kernel internal file (ignored for ENFILE accounting) */
+
#define RW_MASK 1
#define RWA_MASK 2
#define READ 0
@@ -640,6 +646,7 @@ struct file {
atomic_t f_count;
unsigned int f_flags;
mode_t f_mode;
+ unsigned short f_kernel_flags;
loff_t f_pos;
struct fown_struct f_owner;
unsigned int f_uid, f_gid;
@@ -1382,6 +1389,7 @@ extern long do_sys_open(int fdf, const c
int mode);
extern struct file *filp_open(const char *, int, int);
extern struct file * dentry_open(struct dentry *, struct vfsmount *, int);
+extern struct file * dentry_open_kernel(struct dentry *, struct vfsmount *, int);
extern int filp_close(struct file *, fl_owner_t id);
extern char * getname(const char __user *);

@@ -1583,6 +1591,7 @@ static inline void insert_inode_hash(str
}

extern struct file * get_empty_filp(void);
+extern struct file * get_empty_kernel_filp(unsigned short fkflags);
extern void file_move(struct file *f, struct list_head *list);
extern void file_kill(struct file *f);
struct bio;
@@ -1608,6 +1617,7 @@ extern ssize_t generic_file_direct_write
unsigned long *, loff_t, loff_t *, size_t, size_t);
extern ssize_t generic_file_buffered_write(struct kiocb *, const struct iovec *,
unsigned long, loff_t, loff_t *, size_t, ssize_t);
+extern int generic_file_buffered_write_one_kernel_page(struct file *, pgoff_t, struct page *);
extern ssize_t do_sync_read(struct file *filp, char __user *buf, size_t len, loff_t *ppos);
extern ssize_t do_sync_write(struct file *filp, const char __user *buf, size_t len, loff_t *ppos);
ssize_t generic_file_write_nolock(struct file *file, const struct iovec *iov,
diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 76eaeff..8a0d4f8 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -787,6 +787,7 @@ enum
FS_AIO_NR=18, /* current system-wide number of aio requests */
FS_AIO_MAX_NR=19, /* system-wide maximum number of aio requests */
FS_INOTIFY=20, /* inotify submenu */
+ FS_FILE_KERNEL=21, /* int: number of internal kernel files */
};

/* /proc/sys/fs/quota/ */
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index e82726f..f849104 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -53,6 +53,9 @@ #include <asm/processor.h>
extern int proc_nr_files(ctl_table *table, int write, struct file *filp,
void __user *buffer, size_t *lenp, loff_t *ppos);

+extern int proc_files_kernel(ctl_table *table, int write, struct file *filp,
+ void __user *buffer, size_t *lenp, loff_t *ppos);
+
#if defined(CONFIG_SYSCTL)

/* External variables not in a header file. */
@@ -956,6 +959,14 @@ static ctl_table fs_table[] = {
.proc_handler = &proc_dointvec,
},
{
+ .ctl_name = FS_FILE_KERNEL,
+ .procname = "file-kernel",
+ .data = &files_stat,
+ .maxlen = 1*sizeof(int),
+ .mode = 0444,
+ .proc_handler = &proc_files_kernel,
+ },
+ {
.ctl_name = FS_DENTRY,
.procname = "dentry-state",
.data = &dentry_stat,
-
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