Hi,
The following patch should fix the OOM deadlock condition caused by
prune_icache(), and improve its performance significantly.
The OOM deadlock can happen because prune_icache() tries to sync _all_
dirty inodes (under PF_MEMALLOC) on the system before trying to free a
portion of the clean unused inodes.
The patch also changes prune_icache() to free clean inodes first, and then
sync _unused_ ones if needed. In case (nr_free_pages < freepages.low) the
code writes one inode synchronously and returns (to avoid the OOM
deadlock).
Patch against 2.4.4-pre1.
Comments are welcome.
--- fs/inode.c~ Thu Apr 12 21:16:35 2001
+++ fs/inode.c Thu Apr 12 21:49:56 2001
@@ -13,6 +13,8 @@
#include <linux/quotaops.h>
#include <linux/slab.h>
#include <linux/cache.h>
+#include <linux/swap.h>
+#include <linux/swapctl.h>
/*
* New inode.c implementation.
@@ -197,6 +199,34 @@
inodes_stat.nr_unused--;
}
+static inline void __sync_one(struct inode *inode, int sync)
+{
+ unsigned dirty;
+
+ list_del(&inode->i_list);
+ list_add(&inode->i_list, atomic_read(&inode->i_count)
+ ? &inode_in_use
+ : &inode_unused);
+
+ /* Set I_LOCK, reset I_DIRTY */
+ dirty = inode->i_state & I_DIRTY;
+ inode->i_state |= I_LOCK;
+ inode->i_state &= ~I_DIRTY;
+ spin_unlock(&inode_lock);
+
+ filemap_fdatasync(inode->i_mapping);
+
+ /* Don't write the inode if only I_DIRTY_PAGES was set */
+ if (dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC))
+ write_inode(inode, sync);
+
+ filemap_fdatawait(inode->i_mapping);
+
+ spin_lock(&inode_lock);
+ inode->i_state &= ~I_LOCK;
+ wake_up(&inode->i_wait);
+}
+
static inline void sync_one(struct inode *inode, int sync)
{
if (inode->i_state & I_LOCK) {
@@ -206,29 +236,7 @@
iput(inode);
spin_lock(&inode_lock);
} else {
- unsigned dirty;
-
- list_del(&inode->i_list);
- list_add(&inode->i_list, atomic_read(&inode->i_count)
- ? &inode_in_use
- : &inode_unused);
- /* Set I_LOCK, reset I_DIRTY */
- dirty = inode->i_state & I_DIRTY;
- inode->i_state |= I_LOCK;
- inode->i_state &= ~I_DIRTY;
- spin_unlock(&inode_lock);
-
- filemap_fdatasync(inode->i_mapping);
-
- /* Don't write the inode if only I_DIRTY_PAGES was set */
- if (dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC))
- write_inode(inode, sync);
-
- filemap_fdatawait(inode->i_mapping);
-
- spin_lock(&inode_lock);
- inode->i_state &= ~I_LOCK;
- wake_up(&inode->i_wait);
+ __sync_one(inode, sync);
}
}
@@ -236,10 +244,42 @@
{
struct list_head * tmp;
- while ((tmp = head->prev) != head)
+ while ((tmp = head->prev) != head)
sync_one(list_entry(tmp, struct inode, i_list), 0);
}
+static inline int try_to_sync_unused_list(struct list_head *head)
+{
+ struct list_head *tmp = head;
+ struct inode *inode;
+
+ while ((tmp = tmp->prev) != head) {
+ inode = list_entry(tmp, struct inode, i_list);
+
+ if (!(inode->i_state & I_LOCK)
+ && !atomic_read(&inode->i_count)) {
+ /*
+ * We're under PF_MEMALLOC here, and syncing the
+ * inode may have to allocate memory. To avoid
+ * running into a OOM deadlock, we write one
+ * inode synchronously and stop syncing in case
+ * we're under freepages.low
+ */
+
+ int sync = nr_free_pages() < freepages.low;
+ __sync_one(inode, sync);
+ if (sync)
+ return 0;
+ /*
+ * __sync_one moved the inode to another list,
+ * so we have to start looking from the list head.
+ */
+ tmp = head;
+ }
+ }
+ return 1;
+}
+
/**
* sync_inodes
* @dev: device to sync the inodes from.
@@ -273,13 +313,14 @@
/*
* Called with the spinlock already held..
*/
-static void sync_all_inodes(void)
+static void try_to_sync_unused_inodes(void)
{
struct super_block * sb = sb_entry(super_blocks.next);
for (; sb != sb_entry(&super_blocks); sb = sb_entry(sb->s_list.next)) {
if (!sb->s_dev)
continue;
- sync_list(&sb->s_dirty);
+ if (!try_to_sync_unused_list(&sb->s_dirty))
+ break;
}
}
@@ -506,13 +547,12 @@
{
LIST_HEAD(list);
struct list_head *entry, *freeable = &list;
- int count = 0;
+ int count = 0, synced = 0;
struct inode * inode;
spin_lock(&inode_lock);
- /* go simple and safe syncing everything before starting */
- sync_all_inodes();
+free_unused:
entry = inode_unused.prev;
while (entry != &inode_unused)
{
@@ -539,6 +579,20 @@
spin_unlock(&inode_lock);
dispose_list(freeable);
+
+ /*
+ * If we freed enough clean inodes, avoid writing
+ * dirty ones. Also giveup if we already tried to
+ * sync dirty inodes.
+ */
+ if (!goal || synced)
+ return;
+
+ synced = 1;
+
+ spin_lock(&inode_lock);
+ try_to_sync_unused_inodes();
+ goto free_unused;
}
void shrink_icache_memory(int priority, int gfp_mask)
-
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