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authorNick Piggin <npiggin@kernel.dk>2011-01-07 17:49:39 +1100
committerNick Piggin <npiggin@kernel.dk>2011-01-07 17:50:23 +1100
commit58db63d086790eec2ed433f9d8c4962239809cf8 (patch)
treee8fa4238167f92bb0dbded4d2df1498d8c4e9404
parentb5c84bf6f6fa3a7dfdcb556023a62953574b60ee (diff)
fs: dcache avoid starvation in dcache multi-step operations
Long lived dcache "multi-step" operations which retry on rename seq can be starved with a lot of rename activity. If they fail after the 1st pass, take the rename_lock for writing to avoid further starvation. Signed-off-by: Nick Piggin <npiggin@kernel.dk>
-rw-r--r--fs/dcache.c56
1 files changed, 42 insertions, 14 deletions
diff --git a/fs/dcache.c b/fs/dcache.c
index 0dbae053b664..bf6294a20f0e 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -973,10 +973,11 @@ int have_submounts(struct dentry *parent)
struct dentry *this_parent;
struct list_head *next;
unsigned seq;
+ int locked = 0;
-rename_retry:
- this_parent = parent;
seq = read_seqbegin(&rename_lock);
+again:
+ this_parent = parent;
if (d_mountpoint(parent))
goto positive;
@@ -1021,7 +1022,7 @@ resume:
/* might go back up the wrong parent if we have had a rename
* or deletion */
if (this_parent != child->d_parent ||
- read_seqretry(&rename_lock, seq)) {
+ (!locked && read_seqretry(&rename_lock, seq))) {
spin_unlock(&this_parent->d_lock);
rcu_read_unlock();
goto rename_retry;
@@ -1031,13 +1032,22 @@ resume:
goto resume;
}
spin_unlock(&this_parent->d_lock);
- if (read_seqretry(&rename_lock, seq))
+ if (!locked && read_seqretry(&rename_lock, seq))
goto rename_retry;
+ if (locked)
+ write_sequnlock(&rename_lock);
return 0; /* No mount points found in tree */
positive:
- if (read_seqretry(&rename_lock, seq))
+ if (!locked && read_seqretry(&rename_lock, seq))
goto rename_retry;
+ if (locked)
+ write_sequnlock(&rename_lock);
return 1;
+
+rename_retry:
+ locked = 1;
+ write_seqlock(&rename_lock);
+ goto again;
}
EXPORT_SYMBOL(have_submounts);
@@ -1061,11 +1071,11 @@ static int select_parent(struct dentry * parent)
struct list_head *next;
unsigned seq;
int found = 0;
+ int locked = 0;
-rename_retry:
- this_parent = parent;
seq = read_seqbegin(&rename_lock);
-
+again:
+ this_parent = parent;
spin_lock(&this_parent->d_lock);
repeat:
next = this_parent->d_subdirs.next;
@@ -1127,7 +1137,7 @@ resume:
/* might go back up the wrong parent if we have had a rename
* or deletion */
if (this_parent != child->d_parent ||
- read_seqretry(&rename_lock, seq)) {
+ (!locked && read_seqretry(&rename_lock, seq))) {
spin_unlock(&this_parent->d_lock);
rcu_read_unlock();
goto rename_retry;
@@ -1138,9 +1148,18 @@ resume:
}
out:
spin_unlock(&this_parent->d_lock);
- if (read_seqretry(&rename_lock, seq))
+ if (!locked && read_seqretry(&rename_lock, seq))
goto rename_retry;
+ if (locked)
+ write_sequnlock(&rename_lock);
return found;
+
+rename_retry:
+ if (found)
+ return found;
+ locked = 1;
+ write_seqlock(&rename_lock);
+ goto again;
}
/**
@@ -2655,10 +2674,11 @@ void d_genocide(struct dentry *root)
struct dentry *this_parent;
struct list_head *next;
unsigned seq;
+ int locked = 0;
-rename_retry:
- this_parent = root;
seq = read_seqbegin(&rename_lock);
+again:
+ this_parent = root;
spin_lock(&this_parent->d_lock);
repeat:
next = this_parent->d_subdirs.next;
@@ -2703,7 +2723,7 @@ resume:
/* might go back up the wrong parent if we have had a rename
* or deletion */
if (this_parent != child->d_parent ||
- read_seqretry(&rename_lock, seq)) {
+ (!locked && read_seqretry(&rename_lock, seq))) {
spin_unlock(&this_parent->d_lock);
rcu_read_unlock();
goto rename_retry;
@@ -2713,8 +2733,16 @@ resume:
goto resume;
}
spin_unlock(&this_parent->d_lock);
- if (read_seqretry(&rename_lock, seq))
+ if (!locked && read_seqretry(&rename_lock, seq))
goto rename_retry;
+ if (locked)
+ write_sequnlock(&rename_lock);
+ return;
+
+rename_retry:
+ locked = 1;
+ write_seqlock(&rename_lock);
+ goto again;
}
/**