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Message-Id: <20081023174101.85b59177.toshi.okajima@jp.fujitsu.com>
Date: Thu, 23 Oct 2008 17:41:01 +0900
From: Toshiyuki Okajima <toshi.okajima@...fujitsu.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-ext4@...r.kernel.org, sct@...hat.com
Subject: Re: [RFC][PATCH] JBD: release checkpoint journal heads through
try_to_release_page when the memory is exhausted
Hi Andrew.
> > rather costly. An alternative might be to implement a shrinker
> > callback function for the journal_head slab cache. Did you consider
> > this?
> Yes.
> But the unused-list and counters are required by managing the shrink targets("journal head")
> if we implement a shrinker.
> I thought that comparatively big code changes were necessary for jbd to accomplish it.
> However I will try it.
I managed to build a shrinker callback function for the journal_head slab cache.
This code size is less than before but the logic of it seems to be more complex
than before.
However, I haven't got any troubles while I am testing some easy load operations
on the fixed kernel.
But I think a system may hang up if concurrently several journal_head shrinker
are executed.
So, I will retry to build more appropriate fix.
Please give me comments if you have a nicer idea.
------------------------------------------------------------------------------
The direct data blocks can be released by the member function, releasepage()
of their mapping.
(They have the mapping of their filesystem i-node.)
On the other hand, the indirect data blocks (ext3) are attempted to be released
by try_to_free_buffers().
Because its mapping is a block device, and a block device doesn't have
own a member function to release a page.
But try_to_free_buffers() is a generic function which releases a buffer_head,
and no buffer_head can be released if a buffer_head has private data
(like journal_head) because the buffer_head reference counter is bigger than 0.
Therefore, a buffer_head cannot be released by try_to_free_buffers() even if
its private data can be released.
As a result, oom-killer may happen when a system memory is exhausted even if
a lot of private data can be released.
To solve this situation, a shrinker of journal_heads is required.
A shrinker was made by referring to logics such as shrink_icache_memory.
In order to shrink journal_heads, it is necessary to manage a list of
journal_heads which are required to be checkpointed all over the filesystems
with jbd.
Timing from which the newly additional list is operated:
- when a journal_head is registered into a checkpoint list. It is also
registered into an overall checkpoint list (newly additional list).
- when a journal_head is removed from a checkpoint list. It is also removed
from an overall checkpoint list (newly additional list).
- while a shrinker is working.
A shrinker scans only a necessary number of journal_heads which are connected
from a new list, and releases ones if possible.
Therefore it becomes difficult for oom-killer to happen than before.
Signed-off-by: Toshiyuki Okajima <toshi.okajima@...fujitsu.com>
---
fs/jbd/checkpoint.c | 77 +++++++++++++++++++++++++++++++++++++++++++
fs/jbd/journal.c | 2 +
include/linux/journal-head.h | 7 +++
3 files changed, 86 insertions(+)
diff -Nurp linux-2.6.27.1.org/fs/jbd/checkpoint.c linux-2.6.27.1/fs/jbd/checkpoint.c
--- linux-2.6.27.1.org/fs/jbd/checkpoint.c 2008-10-16 08:02:53.000000000 +0900
+++ linux-2.6.27.1/fs/jbd/checkpoint.c 2008-10-23 15:07:14.000000000 +0900
@@ -24,6 +24,14 @@
#include <linux/slab.h>
/*
+ * Used for shrinking journal_heads whose I/O are completed
+ */
+static DEFINE_SPINLOCK(jbd_global_lock);
+static LIST_HEAD(jbd_checkpoint_list);
+static int jbd_jh_cache_pressure = 10;
+static int jbd_nr_checkpoint_jh = 0;
+
+/*
* Unlink a buffer from a transaction checkpoint list.
*
* Called with j_list_lock held.
@@ -595,6 +603,10 @@ int __journal_remove_checkpoint(struct j
__buffer_unlink(jh);
jh->b_cp_transaction = NULL;
+ spin_lock(&jbd_global_lock);
+ list_del_init(&jh->b_checkpoint_list);
+ jbd_nr_checkpoint_jh--;
+ spin_unlock(&jbd_global_lock);
if (transaction->t_checkpoint_list != NULL ||
transaction->t_checkpoint_io_list != NULL)
@@ -655,8 +667,73 @@ void __journal_insert_checkpoint(struct
jh->b_cpnext->b_cpprev = jh;
}
transaction->t_checkpoint_list = jh;
+ spin_lock(&jbd_global_lock);
+ list_add(&jh->b_checkpoint_list, &jbd_checkpoint_list);
+ jbd_nr_checkpoint_jh++;
+ spin_unlock(&jbd_global_lock);
+}
+
+static void try_to_free_cp_buf(journal_t *journal, transaction_t *transaction, struct journal_head *jh)
+{
+ transaction_t *transaction2;
+
+ spin_lock(&journal->j_list_lock);
+ if (!list_empty(&jh->b_checkpoint_list)) {
+ transaction2 = jh->b_cp_transaction;
+ BUG_ON(transaction2 == NULL);
+ if (transaction == transaction2) {
+ jbd_lock_bh_state(jh2bh(jh));
+ __try_to_free_cp_buf(jh);
+ }
+ }
+ spin_unlock(&journal->j_list_lock);
}
+static void prune_jbd_jhcache(int nr)
+{
+ struct journal_head *jh;
+ struct list_head *tmp;
+ journal_t *journal;
+ transaction_t *transaction;
+
+ BUG_ON(nr < 0);
+ for (; nr; nr--) {
+ spin_lock(&jbd_global_lock);
+ if ((tmp = jbd_checkpoint_list.prev) == &jbd_checkpoint_list) {
+ spin_unlock(&jbd_global_lock);
+ break;
+ }
+ list_move(tmp, &jbd_checkpoint_list);
+ jh = list_entry(tmp, struct journal_head, b_checkpoint_list);
+ /* Protect a jh from being removed while operating */
+ journal_grab_journal_head(jh2bh(jh));
+ transaction = jh->b_cp_transaction;
+ BUG_ON(transaction == NULL);
+ journal = transaction->t_journal;
+ spin_unlock(&jbd_global_lock);
+ /* Releasing a jh from checkpoint list if possible */
+ try_to_free_cp_buf(journal, transaction, jh);
+ /* For previous count up (actually releasing a jh here) */
+ journal_put_journal_head(jh);
+ cond_resched();
+ }
+}
+
+static int shrink_jbd_jhcache_memory(int nr, gfp_t gfp_mask)
+{
+ if (nr) {
+ if (!(gfp_mask & __GFP_FS))
+ return -1;
+ prune_jbd_jhcache(nr);
+ }
+ return (jbd_nr_checkpoint_jh*100)/jbd_jh_cache_pressure;
+}
+
+struct shrinker jbd_jh_shrinker = {
+ .shrink = shrink_jbd_jhcache_memory,
+ .seeks = DEFAULT_SEEKS,
+};
+
/*
* We've finished with this transaction structure: adios...
*
diff -Nurp linux-2.6.27.1.org/fs/jbd/journal.c linux-2.6.27.1/fs/jbd/journal.c
--- linux-2.6.27.1.org/fs/jbd/journal.c 2008-10-16 08:02:53.000000000 +0900
+++ linux-2.6.27.1/fs/jbd/journal.c 2008-10-23 15:00:44.000000000 +0900
@@ -1890,6 +1890,7 @@ static inline void jbd_remove_debugfs_en
#endif
+extern struct shrinker jbd_jh_shrinker;
struct kmem_cache *jbd_handle_cache;
static int __init journal_init_handle_cache(void)
@@ -1903,6 +1904,7 @@ static int __init journal_init_handle_ca
printk(KERN_EMERG "JBD: failed to create handle cache\n");
return -ENOMEM;
}
+ register_shrinker(&jbd_jh_shrinker);
return 0;
}
diff -Nurp linux-2.6.27.1.org/include/linux/journal-head.h linux-2.6.27.1/include/linux/journal-head.h
--- linux-2.6.27.1.org/include/linux/journal-head.h 2008-10-16 08:02:53.000000000 +0900
+++ linux-2.6.27.1/include/linux/journal-head.h 2008-10-23 15:00:44.000000000 +0900
@@ -87,6 +87,13 @@ struct journal_head {
* [j_list_lock]
*/
struct journal_head *b_cpnext, *b_cpprev;
+
+ /*
+ * Checkpoint journal head list
+ * all over filesystems with jbd in order to shrink.
+ * [jbd_global_lock]
+ */
+ struct list_head b_checkpoint_list;
};
#endif /* JOURNAL_HEAD_H_INCLUDED */
--
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