Patch "jbd2: Fix unreclaimed pages after truncate in data=journal mode" has been added to the 3.10-stable tree

This is a note to let you know that I've just added the patch titled

jbd2: Fix unreclaimed pages after truncate in data=journal mode

to the 3.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
jbd2-fix-unreclaimed-pages-after-truncate-in-data-journal-mode.patch
and it can be found in the queue-3.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Jan Kara <[email protected]>
Date: Tue, 24 Nov 2015 15:34:35 -0500
Subject: jbd2: Fix unreclaimed pages after truncate in data=journal mode

From: Jan Kara <[email protected]>

commit bc23f0c8d7ccd8d924c4e70ce311288cb3e61ea8 upstream.

Ted and Namjae have reported that truncated pages don't get timely reclaimed after being truncated in data=journal mode. The following test triggers the issue easily:

for (i = 0; i < 1000; i++) {
	pwrite(fd, buf, 1024*1024, 0);
	fsync(fd);
	fsync(fd);
	ftruncate(fd, 0);
}

The reason is that journal_unmap_buffer() finds that truncated buffers are not journalled (jh->b_transaction == NULL), they are part of checkpoint list of a transaction (jh->b_cp_transaction != NULL) and have been already written out (!buffer_dirty(bh)). We clean such buffers but we leave them in the checkpoint list. Since checkpoint transaction holds a reference to the journal head, these buffers cannot be released until the checkpoint transaction is cleaned up. And at that point we don't call release_buffer_page() anymore so pages detached from mapping are lingering in the system waiting for reclaim to find them and free them.

Fix the problem by removing buffers from transaction checkpoint lists when journal_unmap_buffer() finds out they don't have to be there anymore.

---
 fs/jbd2/transaction.c |    2 ++
 1 file changed, 2 insertions(+)

@@ -1936,6 +1936,7 @@ static int journal_unmap_buffer(journal_
 
 		if (!buffer_dirty(bh)) {
 			/* bdflush has written it.  We can drop it now */
+			__jbd2_journal_remove_checkpoint(jh);
 			goto zap_buffer;
 		}
 

@@ -1965,6 +1966,7 @@ static int journal_unmap_buffer(journal_
 				/* The orphan record's transaction has
 				 * committed.  We can cleanse this buffer */
 				clear_buffer_jbddirty(bh);
+				__jbd2_journal_remove_checkpoint(jh);
 				goto zap_buffer;
 			}
 		}

Patches currently in stable-queue which might be from [email protected] are

queue-3.10/jbd2-fix-unreclaimed-pages-after-truncate-in-data-journal-mode.patch