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Date: Sat, 27 Nov 2010 20:44:50 +1100
From: Nick Piggin <npiggin@...nel.dk>
To: linux-fsdevel@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Subject: [PATCH 20/46] 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@...nel.dk>
---
fs/dcache.c | 56 ++++++++++++++++++++++++++++++++++++++++++--------------
1 files changed, 42 insertions(+), 14 deletions(-)
diff --git a/fs/dcache.c b/fs/dcache.c
index c4b2c5e..73f5552 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -937,10 +937,11 @@ 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;
@@ -985,7 +986,7 @@ 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;
@@ -995,13 +996,22 @@ 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);
@@ -1025,11 +1035,11 @@ 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;
@@ -1091,7 +1101,7 @@ 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;
@@ -1102,9 +1112,18 @@ 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;
}
/**
@@ -2602,10 +2621,11 @@ 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;
@@ -2650,7 +2670,7 @@ 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;
@@ -2660,8 +2680,16 @@ 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;
}
/**
--
1.7.1
--
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