The tracking and limit of negative dentries in a filesystem is a useful
addition. However, for users who want to reduce the kernel size as much
as possible, this feature will probably be on the chopping block. To
suit those users, a default-y config option DCACHE_LIMIT_NEG_ENTRY is
added so that the negative dentry limiting code can be configured out,
if necessary.
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
---
fs/Kconfig | 10 ++++++++++
fs/dcache.c | 29 +++++++++++++++++++++++------
include/linux/dcache.h | 2 ++
kernel/sysctl.c | 2 ++
4 files changed, 37 insertions(+), 6 deletions(-)
diff --git a/fs/Kconfig b/fs/Kconfig
index ac474a6..b521941 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -113,6 +113,16 @@ source "fs/autofs/Kconfig"
source "fs/fuse/Kconfig"
source "fs/overlayfs/Kconfig"
+#
+# Track and limit the number of negative dentries allowed in the system.
+#
+config DCACHE_LIMIT_NEG_ENTRY
+ bool "Track & limit negative dcache entries"
+ default y
+ help
+ This option enables the tracking and limiting of the total
+ number of negative dcache entries allowable in the filesystem.
+
menu "Caches"
source "fs/fscache/Kconfig"
diff --git a/fs/dcache.c b/fs/dcache.c
index 843c8be..dccfe39 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -141,6 +141,7 @@ struct dentry_stat_t dentry_stat = {
#define NEG_DENTRY_BATCH (1 << 8)
#define NEG_WARN_PERIOD (60 * HZ) /* Print a warning every min */
+#ifdef CONFIG_DCACHE_LIMIT_NEG_ENTRY
static struct static_key limit_neg_key = STATIC_KEY_INIT_FALSE;
static int neg_dentry_limit_old;
int neg_dentry_limit;
@@ -156,6 +157,7 @@ struct dentry_stat_t dentry_stat = {
unsigned long warn_jiffies; /* Time when last warning is printed */
} ndblk ____cacheline_aligned_in_smp;
proc_handler proc_neg_dentry_limit;
+#endif /* CONFIG_DCACHE_LIMIT_NEG_ENTRY */
static DEFINE_PER_CPU(long, nr_dentry);
static DEFINE_PER_CPU(long, nr_dentry_unused);
@@ -200,7 +202,9 @@ static long get_nr_dentry_neg(void)
for_each_possible_cpu(i)
sum += per_cpu(nr_dentry_neg, i);
+#ifdef CONFIG_DCACHE_LIMIT_NEG_ENTRY
sum += neg_dentry_nfree_init - ndblk.nfree;
+#endif
return sum < 0 ? 0 : sum;
}
@@ -267,6 +271,7 @@ static inline int dentry_string_cmp(const unsigned char *cs, const unsigned char
#endif
+#ifdef CONFIG_DCACHE_LIMIT_NEG_ENTRY
/*
* Decrement negative dentry count if applicable.
*/
@@ -289,12 +294,6 @@ static void __neg_dentry_dec(struct dentry *dentry)
}
}
-static inline void neg_dentry_dec(struct dentry *dentry)
-{
- if (unlikely(d_is_negative(dentry)))
- __neg_dentry_dec(dentry);
-}
-
/*
* Try to decrement the negative dentry free pool by NEG_DENTRY_BATCH.
* The actual decrement returned by the function may be smaller.
@@ -454,6 +453,20 @@ int proc_neg_dentry_limit(struct ctl_table *ctl, int write,
return 0;
}
EXPORT_SYMBOL_GPL(proc_neg_dentry_limit);
+#else /* CONFIG_DCACHE_LIMIT_NEG_ENTRY */
+
+static inline void __neg_dentry_dec(struct dentry *dentry)
+{
+ this_cpu_dec(nr_dentry_neg);
+}
+
+#endif /* CONFIG_DCACHE_LIMIT_NEG_ENTRY */
+
+static inline void neg_dentry_dec(struct dentry *dentry)
+{
+ if (unlikely(d_is_negative(dentry)))
+ __neg_dentry_dec(dentry);
+}
static inline int dentry_cmp(const struct dentry *dentry, const unsigned char *ct, unsigned tcount)
{
@@ -642,6 +655,7 @@ static void d_lru_add(struct dentry *dentry)
dentry->d_flags |= DCACHE_LRU_LIST;
this_cpu_inc(nr_dentry_unused);
if (d_is_negative(dentry)) {
+#ifdef CONFIG_DCACHE_LIMIT_NEG_ENTRY
if (dentry->d_flags & DCACHE_NEW_NEGATIVE) {
dentry->d_flags &= ~DCACHE_NEW_NEGATIVE;
if (unlikely(neg_dentry_inc(dentry) < 0)) {
@@ -658,6 +672,7 @@ static void d_lru_add(struct dentry *dentry)
&dentry->d_sb->s_dentry_lru, &dentry->d_lru));
return;
}
+#endif
/*
* We don't do limit check for existing negative
* dentries.
@@ -3431,7 +3446,9 @@ static void __init dcache_init(void)
SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|SLAB_MEM_SPREAD|SLAB_ACCOUNT,
d_iname);
+#ifdef CONFIG_DCACHE_LIMIT_NEG_ENTRY
raw_spin_lock_init(&ndblk.nfree_lock);
+#endif
/* Hash may have been set up in dcache_init_early */
if (!hashdist)
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 934a6d9..11729a1 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -612,10 +612,12 @@ struct name_snapshot {
void take_dentry_name_snapshot(struct name_snapshot *, struct dentry *);
void release_dentry_name_snapshot(struct name_snapshot *);
+#ifdef CONFIG_DCACHE_LIMIT_NEG_ENTRY
/*
* Negative dentry related declarations.
*/
extern int neg_dentry_limit;
extern int neg_dentry_enforce;
+#endif
#endif /* __LINUX_DCACHE_H */
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index a24101e..732c624 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1851,6 +1851,7 @@ static int sysrq_sysctl_handler(struct ctl_table *table, int write,
.proc_handler = proc_dointvec_minmax,
.extra1 = &one,
},
+#ifdef CONFIG_DCACHE_LIMIT_NEG_ENTRY
{
.procname = "neg-dentry-limit",
.data = &neg_dentry_limit,
@@ -1869,6 +1870,7 @@ static int sysrq_sysctl_handler(struct ctl_table *table, int write,
.extra1 = &zero,
.extra2 = &one,
},
+#endif
{ }
};
--
1.8.3.1
