On 05/14/2013 10:59 AM, Dave Chinner wrote: > On Sun, May 12, 2013 at 10:13:30PM +0400, Glauber Costa wrote: >> From: Dave Chinner <dchinner@xxxxxxxxxx> >> >> [ glommer: don't reintroduce double decrement of nr_unused_dentries, >> adapted for new LRU return codes ] >> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx> >> Signed-off-by: Glauber Costa <glommer@xxxxxxxxxx> >> --- > > I'm seeing a panic on startup in d_kill() with an invalid d_child > list entry with this patch. I haven't got to the bottom of it yet. > My wild guess is that your patch does not prune correctly, as I described in my last message. > ..... > >> void shrink_dcache_sb(struct super_block *sb) >> { >> - LIST_HEAD(tmp); >> - >> - spin_lock(&sb->s_dentry_lru_lock); >> - while (!list_empty(&sb->s_dentry_lru)) { >> - list_splice_init(&sb->s_dentry_lru, &tmp); >> - >> - /* >> - * account for removal here so we don't need to handle it later >> - * even though the dentry is no longer on the lru list. >> - */ >> - this_cpu_sub(nr_dentry_unused, sb->s_nr_dentry_unused); >> - sb->s_nr_dentry_unused = 0; >> - >> - spin_unlock(&sb->s_dentry_lru_lock); >> - shrink_dcache_list(&tmp); >> - spin_lock(&sb->s_dentry_lru_lock); >> - } >> - spin_unlock(&sb->s_dentry_lru_lock); >> + list_lru_dispose_all(&sb->s_dentry_lru, shrink_dcache_list); >> } >> EXPORT_SYMBOL(shrink_dcache_sb); > > And here comes the fun part. This doesn't account for the > dentries that are freed from the superblock here. > > So, it needs to be something like: > > void shrink_dcache_sb(struct super_block *sb) > { > unsigned long disposed; > > disposed = list_lru_dispose_all(&sb->s_dentry_lru, > shrink_dcache_list); > > this_cpu_sub(nr_dentry_unused, disposed); > } > > But, therein lies a problem. nr_dentry_unused is a 32 bit counter, > and we can return a 64 bit value here. So that means we have to bump > nr_dentry_unused to a long, not an int for these per-cpu counters to > work. > > And then there's the problem that the sum of these counters only > uses an int. Which means if we get large numbers of negative values > on different CPU from unmounts, the summation will end up > overflowing and it'll all suck. > > So, Glauber, what do you reckon? I've never likes this stupid > hand-rolled per-cpu counter stuff, and it's causing issues. Should > we just convert them to generic per-cpu counters because they are > 64bit clean and just handle out-of-range sums in the /proc update > code? > One option would be to add the following patch to the beginning of the series.
diff --git a/fs/dcache.c b/fs/dcache.c index 3a3adc4..a8be4c9 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -116,12 +116,12 @@ struct dentry_stat_t dentry_stat = { .age_limit = 45, }; -static DEFINE_PER_CPU(unsigned int, nr_dentry); -static DEFINE_PER_CPU(unsigned int, nr_dentry_unused); +static DEFINE_PER_CPU(long, nr_dentry); +static DEFINE_PER_CPU(long, nr_dentry_unused); #if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS) /* scan possible cpus instead of online and avoid worrying about CPU hotplug. */ -static int get_nr_dentry(void) +static long get_nr_dentry(void) { int i; int sum = 0; @@ -130,7 +130,7 @@ static int get_nr_dentry(void) return sum < 0 ? 0 : sum; } -static int get_nr_dentry_unused(void) +static long get_nr_dentry_unused(void) { int i; int sum = 0; @@ -144,7 +144,7 @@ int proc_nr_dentry(ctl_table *table, int write, void __user *buffer, { dentry_stat.nr_dentry = get_nr_dentry(); dentry_stat.nr_unused = get_nr_dentry_unused(); - return proc_dointvec(table, write, buffer, lenp, ppos); + return proc_doulongvec_minmax(table, write, buffer, lenp, ppos); } #endif diff --git a/include/linux/dcache.h b/include/linux/dcache.h index 4d24a12..bd08285 100644 --- a/include/linux/dcache.h +++ b/include/linux/dcache.h @@ -54,11 +54,11 @@ struct qstr { #define hashlen_len(hashlen) ((u32)((hashlen) >> 32)) struct dentry_stat_t { - int nr_dentry; - int nr_unused; - int age_limit; /* age in seconds */ - int want_pages; /* pages requested by system */ - int dummy[2]; + long nr_dentry; + long nr_unused; + long age_limit; /* age in seconds */ + long want_pages; /* pages requested by system */ + long dummy[2]; }; extern struct dentry_stat_t dentry_stat; diff --git a/include/linux/fs.h b/include/linux/fs.h index 67e1040..e875f60 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1267,12 +1267,12 @@ struct super_block { /* s_dentry_lru_lock protects s_dentry_lru and s_nr_dentry_unused */ spinlock_t s_dentry_lru_lock ____cacheline_aligned_in_smp; struct list_head s_dentry_lru; /* unused dentry lru */ - int s_nr_dentry_unused; /* # of dentry on lru */ + long s_nr_dentry_unused; /* # of dentry on lru */ /* s_inode_lru_lock protects s_inode_lru and s_nr_inodes_unused */ spinlock_t s_inode_lru_lock ____cacheline_aligned_in_smp; struct list_head s_inode_lru; /* unused inode lru */ - int s_nr_inodes_unused; /* # of inodes on lru */ + long s_nr_inodes_unused; /* # of inodes on lru */ struct block_device *s_bdev; struct backing_dev_info *s_bdi; diff --git a/kernel/sysctl.c b/kernel/sysctl.c index 9edcf45..0dc51c0 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -1493,7 +1493,7 @@ static struct ctl_table fs_table[] = { { .procname = "dentry-state", .data = &dentry_stat, - .maxlen = 6*sizeof(int), + .maxlen = 6*sizeof(long), .mode = 0444, .proc_handler = proc_nr_dentry, },