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Message-ID: <20100723141054.GE13090@thunk.org>
Date: Fri, 23 Jul 2010 10:10:54 -0400
From: Ted Ts'o <tytso@....edu>
To: David Rientjes <rientjes@...gle.com>
Cc: Jan Kara <jack@...e.cz>, Andrew Morton <akpm@...ux-foundation.org>,
Andreas Dilger <adilger@....com>,
Jiri Kosina <jkosina@...e.cz>, linux-mm@...ck.org,
linux-ext4@...r.kernel.org
Subject: Re: [patch 6/6] jbd2: remove dependency on __GFP_NOFAIL
On Thu, Jul 22, 2010 at 04:24:23PM -0700, David Rientjes wrote:
>
> I didn't think about converting the existing GFP_NOFS | __GFP_NOFAIL
> callers into the do-while loop above until you mentioned it, thanks. I'll
> send patches to do that shortly.
Here's what I'm planning on queueing for the next merge window, along
with patches to ext4 to use jbd2__journal_start(..., GFP_KERNEL) in
places where we can afford to fail. After doing some analysis, the
places where we can afford to fail are also the places where we can
use GFP_KERNEL instead of GFP_NOFS, so conveniently, I'm using the
lack of __GFP_FS to indicate that we should do the retry loop in
start_this_handle(). I also added the congestion_wait() call since
there's no point busy-looping the CPU while we're waiting for pages to
get swapped or paged out.
Comments would be appreciated.
- Ted
>From 814be805d5e3d12343e590631ff9bc2d65c8f60a Mon Sep 17 00:00:00 2001
From: Theodore Ts'o <tytso@....edu>
Date: Fri, 23 Jul 2010 10:06:53 -0400
Subject: [PATCH] jbd2: Remove __GFP_NOFAIL from jbd2 layer
__GFP_NOFAIL is going away, so add our own retry loop. Also add
jbd2__journal_start() and jbd2__journal_restart() which take a gfp
mask, so that file systems can optionally (re)start transaction
handles using GFP_KERNEL. If they do this, then they need to be
prepared to handle receiving an PTR_ERR(-ENOMEM) error, and be ready
to reflect that error up to userspace.
Signed-off-by: "Theodore Ts'o" <tytso@....edu>
---
fs/jbd2/journal.c | 14 +++++++++--
fs/jbd2/transaction.c | 60 +++++++++++++++++++++++++++++++++---------------
include/linux/jbd2.h | 4 ++-
3 files changed, 55 insertions(+), 23 deletions(-)
diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index f7bf157..eb84fbd 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -48,8 +48,6 @@
#include <asm/uaccess.h>
#include <asm/page.h>
-EXPORT_SYMBOL(jbd2_journal_start);
-EXPORT_SYMBOL(jbd2_journal_restart);
EXPORT_SYMBOL(jbd2_journal_extend);
EXPORT_SYMBOL(jbd2_journal_stop);
EXPORT_SYMBOL(jbd2_journal_lock_updates);
@@ -311,7 +309,17 @@ int jbd2_journal_write_metadata_buffer(transaction_t *transaction,
*/
J_ASSERT_BH(bh_in, buffer_jbddirty(bh_in));
- new_bh = alloc_buffer_head(GFP_NOFS|__GFP_NOFAIL);
+retry_alloc:
+ new_bh = alloc_buffer_head(GFP_NOFS);
+ if (!new_bh) {
+ /*
+ * Failure is not an option, but __GFP_NOFAIL is going
+ * away; so we retry ourselves here.
+ */
+ congestion_wait(BLK_RW_ASYNC, HZ/50);
+ goto retry_alloc;
+ }
+
/* keep subsequent assertions sane */
new_bh->b_state = 0;
init_buffer(new_bh, NULL, NULL);
diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index e214d68..43241c0 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -83,30 +83,39 @@ jbd2_get_transaction(journal_t *journal, transaction_t *transaction)
* transaction's buffer credits.
*/
-static int start_this_handle(journal_t *journal, handle_t *handle)
+static int start_this_handle(journal_t *journal, handle_t *handle,
+ int gfp_mask)
{
transaction_t *transaction;
int needed;
int nblocks = handle->h_buffer_credits;
transaction_t *new_transaction = NULL;
- int ret = 0;
unsigned long ts = jiffies;
if (nblocks > journal->j_max_transaction_buffers) {
printk(KERN_ERR "JBD: %s wants too many credits (%d > %d)\n",
current->comm, nblocks,
journal->j_max_transaction_buffers);
- ret = -ENOSPC;
- goto out;
+ return -ENOSPC;
}
alloc_transaction:
if (!journal->j_running_transaction) {
- new_transaction = kzalloc(sizeof(*new_transaction),
- GFP_NOFS|__GFP_NOFAIL);
+ retry_alloc:
+ new_transaction = kzalloc(sizeof(*new_transaction), gfp_mask);
if (!new_transaction) {
- ret = -ENOMEM;
- goto out;
+ /*
+ * If __GFP_FS is not present, then we may be
+ * being called from inside the fs writeback
+ * layer, so we MUST NOT fail. Since
+ * __GFP_NOFAIL is going away, we will arrange
+ * to retry the allocation ourselves.
+ */
+ if ((gfp & __GFP_FS) == 0) {
+ congestion_wait(BLK_RW_ASYNC, HZ/50);
+ goto retry_alloc;
+ }
+ return -ENOMEM;
}
}
@@ -123,8 +132,8 @@ repeat_locked:
if (is_journal_aborted(journal) ||
(journal->j_errno != 0 && !(journal->j_flags & JBD2_ACK_ERR))) {
spin_unlock(&journal->j_state_lock);
- ret = -EROFS;
- goto out;
+ kfree(new_transaction);
+ return -EROFS;
}
/* Wait on the journal's transaction barrier if necessary */
@@ -240,10 +249,8 @@ repeat_locked:
spin_unlock(&journal->j_state_lock);
lock_map_acquire(&handle->h_lockdep_map);
-out:
- if (unlikely(new_transaction)) /* It's usually NULL */
- kfree(new_transaction);
- return ret;
+ kfree(new_transaction);
+ return 0;
}
static struct lock_class_key jbd2_handle_key;
@@ -278,7 +285,7 @@ static handle_t *new_handle(int nblocks)
*
* Return a pointer to a newly allocated handle, or NULL on failure
*/
-handle_t *jbd2_journal_start(journal_t *journal, int nblocks)
+handle_t *jbd2__journal_start(journal_t *journal, int nblocks, int gfp_mask)
{
handle_t *handle = journal_current_handle();
int err;
@@ -298,7 +305,7 @@ handle_t *jbd2_journal_start(journal_t *journal, int nblocks)
current->journal_info = handle;
- err = start_this_handle(journal, handle);
+ err = start_this_handle(journal, handle, GFP_NOFS);
if (err < 0) {
jbd2_free_handle(handle);
current->journal_info = NULL;
@@ -308,6 +315,15 @@ handle_t *jbd2_journal_start(journal_t *journal, int nblocks)
out:
return handle;
}
+EXPORT_SYMBOL(jbd2__journal_start);
+
+
+handle_t *jbd2_journal_start(journal_t *journal, int nblocks)
+{
+ return jbd2__journal_start(journal, nblocks, GFP_NOFS);
+}
+EXPORT_SYMBOL(jbd2_journal_start);
+
/**
* int jbd2_journal_extend() - extend buffer credits.
@@ -394,8 +410,7 @@ out:
* transaction capabable of guaranteeing the requested number of
* credits.
*/
-
-int jbd2_journal_restart(handle_t *handle, int nblocks)
+int jbd2__journal_restart(handle_t *handle, int nblocks, int gfp_mask)
{
transaction_t *transaction = handle->h_transaction;
journal_t *journal = transaction->t_journal;
@@ -428,10 +443,17 @@ int jbd2_journal_restart(handle_t *handle, int nblocks)
lock_map_release(&handle->h_lockdep_map);
handle->h_buffer_credits = nblocks;
- ret = start_this_handle(journal, handle);
+ ret = start_this_handle(journal, handle, GFP_NOFS);
return ret;
}
+EXPORT_SYMBOL(jbd2__journal_restart);
+
+int jbd2_journal_restart(handle_t *handle, int nblocks)
+{
+ return jbd2__journal_restart(handle, nblocks, GFP_NOFS);
+}
+EXPORT_SYMBOL(jbd2_journal_restart);
/**
* void jbd2_journal_lock_updates () - establish a transaction barrier.
diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index a4d2e9f..5a72bc7 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -1081,7 +1081,9 @@ static inline handle_t *journal_current_handle(void)
*/
extern handle_t *jbd2_journal_start(journal_t *, int nblocks);
-extern int jbd2_journal_restart (handle_t *, int nblocks);
+extern handle_t *jbd2__journal_start(journal_t *, int nblocks, int gfp_mask);
+extern int jbd2_journal_restart(handle_t *, int nblocks);
+extern int jbd2__journal_restart(handle_t *, int nblocks, int gfp_mask);
extern int jbd2_journal_extend (handle_t *, int nblocks);
extern int jbd2_journal_get_write_access(handle_t *, struct buffer_head *);
extern int jbd2_journal_get_create_access (handle_t *, struct buffer_head *);
--
1.7.0.4
--
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