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Subject[PATCH v6 7/7] fs/dcache: Allow deconfiguration of negative dentry code to reduce kernel size
Date
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 tracking and limiting code can be
configured out, if necessary.

Signed-off-by: Waiman Long <longman@redhat.com>
---
fs/Kconfig | 10 ++++++++++
fs/dcache.c | 33 ++++++++++++++++++++++++++++++++-
include/linux/dcache.h | 2 ++
kernel/sysctl.c | 2 ++
4 files changed, 46 insertions(+), 1 deletion(-)

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 43d49d7..d00761e 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -143,6 +143,7 @@ struct dentry_stat_t dentry_stat = {
#define NEG_IS_SB_UMOUNTING(sb) \
unlikely(!(sb)->s_root || !((sb)->s_flags & MS_ACTIVE))

+#ifdef CONFIG_DCACHE_LIMIT_NEG_ENTRY
static struct static_key limit_neg_key = STATIC_KEY_INIT_FALSE;
static int neg_dentry_pc_old;
int neg_dentry_pc;
@@ -166,10 +167,11 @@ struct dentry_stat_t dentry_stat = {
static void d_lru_del(struct dentry *dentry);
static void prune_negative_dentry(struct work_struct *work);
static DECLARE_DELAYED_WORK(prune_neg_dentry_work, prune_negative_dentry);
+static DEFINE_PER_CPU(long, nr_dentry_neg);
+#endif /* CONFIG_DCACHE_LIMIT_NEG_ENTRY */

static DEFINE_PER_CPU(long, nr_dentry);
static DEFINE_PER_CPU(long, nr_dentry_unused);
-static DEFINE_PER_CPU(long, nr_dentry_neg);

#if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)

@@ -203,6 +205,7 @@ static long get_nr_dentry_unused(void)
return sum < 0 ? 0 : sum;
}

+#ifdef CONFIG_DCACHE_LIMIT_NEG_ENTRY
static long get_nr_dentry_neg(void)
{
int i;
@@ -213,6 +216,9 @@ static long get_nr_dentry_neg(void)
sum += neg_dentry_nfree_init - ndblk.nfree;
return sum < 0 ? 0 : sum;
}
+#else
+static long get_nr_dentry_neg(void) { return 0; }
+#endif

int proc_nr_dentry(struct ctl_table *table, int write, void __user *buffer,
size_t *lenp, loff_t *ppos)
@@ -277,6 +283,7 @@ 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.
*/
@@ -455,6 +462,26 @@ int proc_neg_dentry_pc(struct ctl_table *ctl, int write,
return 0;
}
EXPORT_SYMBOL_GPL(proc_neg_dentry_pc);
+#else /* CONFIG_DCACHE_LIMIT_NEG_ENTRY */
+
+static inline void __neg_dentry_dec(struct dentry *dentry)
+{
+}
+
+static inline void neg_dentry_dec(struct dentry *dentry)
+{
+}
+
+static inline void __neg_dentry_inc(struct dentry *dentry, bool retain)
+{
+}
+
+static inline void neg_dentry_inc(struct dentry *dentry)
+{
+}
+
+#endif /* CONFIG_DCACHE_LIMIT_NEG_ENTRY */
+

static inline int dentry_cmp(const struct dentry *dentry, const unsigned char *ct, unsigned tcount)
{
@@ -1485,6 +1512,7 @@ void shrink_dcache_sb(struct super_block *sb)
}
EXPORT_SYMBOL(shrink_dcache_sb);

+#ifdef CONFIG_DCACHE_LIMIT_NEG_ENTRY
/*
* A modified version that attempts to remove a limited number of negative
* dentries as well as some other non-negative dentries at the front.
@@ -1639,6 +1667,7 @@ static void prune_negative_dentry(struct work_struct *work)
deactivate_super(sb);
WRITE_ONCE(ndblk.prune_sb, NULL);
}
+#endif /* CONFIG_DCACHE_LIMIT_NEG_ENTRY */

/**
* enum d_walk_ret - action to talke during tree walk
@@ -3576,7 +3605,9 @@ 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 71a3315..27ffc35 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_pc;
extern int neg_dentry_enforce;
+#endif

#endif /* __LINUX_DCACHE_H */
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 8c008ae..875d5ef 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1852,6 +1852,7 @@ 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-pc",
.data = &neg_dentry_pc,
@@ -1870,6 +1871,7 @@ static int sysrq_sysctl_handler(struct ctl_table *table, int write,
.extra1 = &zero,
.extra2 = &one,
},
+#endif
{ }
};

--
1.8.3.1
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