RE: memory leak: data=journal and {collapse,insert,zero}_range

[Namjae Jeon <namjae.jeon@samsung.com>]

> 
> On Wed, Oct 21, 2015 at 06:44:10PM +0900, Namjae Jeon wrote:
> > > Interestingly we're not seeing these memory leaks on the truncate
> > > path, so I suspect the issue is in how collapse range is clearing
> > > pages from the page cache, especially pages that were freshly written
> > > to the journal by the commit but which hadn't yet been writtten to
> > > disk and then marked as complete so we can allow the relevant
> > > transaction to be checkpointed.  (Although we're not leaking the
> > > journal head structures, but only the buffer heads, so the story most
> > > be a bit more complicated than that.)
> >
> > Okay, Thanks for sharing your view and points !!
> >
> > Currently I can reproduce memory leak issue without collase/insert/zero range.
> > conditions like the following.(collase/insert/zero range are disable with -I -C -z option and add -y
> option instead of -W)
> >   1. small size parition(1GB)
> >   2. run fsx with these options "./fsx -N 30000 -o 128000 -l 500000 -r 4096 -t 512 -w 512 -Z -R -y -
> I -C -z testfile"
> > And same result with generic/091 is showing (buffer_head leak)
> >
> > So I am starting to find root-cause base on your points.
> > I will share the result or the patch.
> 
> Thanks, that's very interesting data point.  So this makes it appear
> that the problem *is* probably with how we deal with checkpointing
> buffers after the pages get discarded using either a truncate or a
> collapse_range, since the 'y' option causes a lot fsync's, and hence
> commits, some of which are happening after a truncate command.
> 
> Thanks for a taking a look at this.  I really appreciate it.
> 
> Cheers,


Hi Ted,

Could you review this patch?

Thanks!
---------------------------------------------------------------------------------
Subject: [PATCH] jbd2: try to free buffers from truncated page after
 checkpoint

when ext4 is mounted in data=journal mode, and truncate operation
such as settatr(size), collopse, insert and zero range are used, there are
are many truncated pages with NULL page->mapping. Such truncated pages
pile up quickly due to truncate_pagecache on data pages associated with journal.
As page->mapping is NULL for such truncated pages, they are not freed
by drop cache(3) or umount. As a result, MemFree in /proc/meminfo decreases
quickly and active buffer_head slab objects grow in /proc/slabinfo.
This patch attempts to free buffers from such pages at the end of jbd2
checkpoint, if pages do not have any busy buffers and NULL mapping. 

---
 fs/jbd2/checkpoint.c | 11 +++++++++++
 fs/jbd2/commit.c     |  2 +-
 include/linux/jbd2.h |  1 +
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c
index 4227dc4..bf68442 100644
--- a/fs/jbd2/checkpoint.c
+++ b/fs/jbd2/checkpoint.c
@@ -529,6 +529,7 @@ int __jbd2_journal_remove_checkpoint(struct journal_head *jh)
 	transaction_t *transaction;
 	journal_t *journal;
 	int ret = 0;
+	struct buffer_head *bh;
 
 	JBUFFER_TRACE(jh, "entry");
 
@@ -538,10 +539,20 @@ int __jbd2_journal_remove_checkpoint(struct journal_head *jh)
 	}
 	journal = transaction->t_journal;
 
+	bh = jh2bh(jh);
+	get_bh(bh);
 	JBUFFER_TRACE(jh, "removing from transaction");
 	__buffer_unlink(jh);
 	jh->b_cp_transaction = NULL;
 	jbd2_journal_put_journal_head(jh);
+	/*
+	 * if journal head is freed, try to free buffers from a truncated
+	 * page, if page buffers are not busy and page->mapping is NULL
+	 */
+	if (!buffer_jbd(bh))
+		release_buffer_page(bh);
+	else
+		__brelse(bh);
 
 	if (transaction->t_checkpoint_list != NULL ||
 	    transaction->t_checkpoint_io_list != NULL)
diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
index b73e021..d94ec3f 100644
--- a/fs/jbd2/commit.c
+++ b/fs/jbd2/commit.c
@@ -63,7 +63,7 @@ static void journal_end_buffer_io_sync(struct buffer_head *bh, int uptodate)
  * Called under lock_journal(), and possibly under journal_datalist_lock.  The
  * caller provided us with a ref against the buffer, and we drop that here.
  */
-static void release_buffer_page(struct buffer_head *bh)
+void release_buffer_page(struct buffer_head *bh)
 {
 	struct page *page;
 
diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index edb640a..523f345 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -1039,6 +1039,7 @@ int __jbd2_update_log_tail(journal_t *journal, tid_t tid, unsigned long block);
 void jbd2_update_log_tail(journal_t *journal, tid_t tid, unsigned long block);
 
 /* Commit management */
+extern void release_buffer_page(struct buffer_head *);
 extern void jbd2_journal_commit_transaction(journal_t *);
 
 /* Checkpoint list management */

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> 
> 					- Ted
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