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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>
This commit is contained in:
Nick Piggin 2011-01-07 17:49:39 +11:00
parent b5c84bf6f6
commit 58db63d086
1 changed files with 42 additions and 14 deletions
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56
fs/dcache.c
View File

@ -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;
}
/**