linux-ext4 - RE: memory leak: data=journal and {collapse,insert,zero}

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Date:	Tue, 20 Oct 2015 21:06:08 +0900
From:	Namjae Jeon <namjae.jeon@...sung.com>
To:	'Theodore Ts'o' <tytso@....edu>
Cc:	linux-ext4@...r.kernel.org
Subject: RE: memory leak: data=journal and {collapse,insert,zero}_range

Hi Ted,

I will check this issue.

Thanks!

> -----Original Message-----
> From: Theodore Ts'o [mailto:tytso@....edu]
> Sent: Sunday, October 18, 2015 1:03 AM
> To: linux-ext4@...r.kernel.org
> Cc: Namjae Jeon
> Subject: memory leak: data=journal and {collapse,insert,zero}_range
> 
> On the last conference call I mentioned that I had recently been
> running into memory leaks with data=journal.  I've traced it down to
> {collapse,insert,zero}_range calls.
> 
> It bisected down to 1ce01c4a199: "ext4: fix COLLAPSE_RANGE test
> failure in data journalling mode", and specifically, this bit of code
> the collapse/insert/zero range functions:
> 
> 	/* Call ext4_force_commit to flush all data in case of data=journal. */
> 	if (ext4_should_journal_data(inode)) {
> 		ret = ext4_force_commit(inode->i_sb);
> 		if (ret)
> 			return ret;
> 	}
> 
> This is needed to prevent data from being lost with the insert and
> collapse range calls.  (It is not obvious to me whether this bit of
> code, and the filemap_write_and_wait_range() call, is needed for
> zero_range, but I haven't had a chance to investigate this more
> deeply.)
> 
> Further investigation shows that the problem seems to be a buffer_head
> leak.  Running generic/091 with data=journal in a loop, and using the
> following between each test runs:
> 
> #!/bin/sh
> # /tmp/hooks/logger
> echo 3 > /proc/sys/vm/drop_caches
> logger $(grep MemFree /proc/meminfo)
> logger $(grep buffer_head /proc/slabinfo)
> logger $(grep jbd2_journal_head /proc/slabinfo)
> 
> what we find is:
> 
> logger: MemFree: 7348684 kB
> logger: buffer_head 608 1600 128 32 1 : tunables 32 16 8 : slabdata 50 50 0 : globalstat 108003 36592
> 3294 0 0 1 0 0 0 : cpustat 102424 6803 101863 6760
> logger: jbd2_journal_head 120 120 136 30 1 : tunables 32 16 8 : slabdata 4 4 0 : globalstat 203 120 4
> 0 0 0 0 0 0 : cpustat 179 14 84 0
> 
> logger: MemFree: 7155576 kB
> logger: buffer_head 45008 65920 128 32 1 : tunables 32 16 8 : slabdata 2060 2060 0 : globalstat 207971
> 79408 5753 0 0 1 0 0 0 : cpustat 354158 14482 311984 11664
> logger: jbd2_journal_head 206 690 136 30 1 : tunables 32 16 8 : slabdata 23 23 128 : globalstat 38817
> 11086 1142 0 0 0 0 0 0 : cpustat 68275 3482 68402 3326
> 
> kernel: logger (5838): drop_caches: 3
> logger: MemFree: 6967656 kB
> logger: buffer_head 89552 111616 128 32 1 : tunables 32 16 8 : slabdata 3488 3488 0 : globalstat
> 308435 124352 7589 0 0 1 0 0 0 : cpustat 606287 22193 522363 16591
> logger: jbd2_journal_head 210 660 136 30 1 : tunables 32 16 8 : slabdata 22 22 128 : globalstat 77205
> 11086 2158 0 0 0 0 0 0 : cpustat 136335 6954 136593 6669
> 
> logger: MemFree: 6780176 kB
> logger: buffer_head 134080 155328 128 32 1 : tunables 32 16 8 : slabdata 4854 4854 0 : globalstat
> 408163 168144 9369 0 0 1 0 0 0 : cpustat 857710 29874 732032 21489
> logger: jbd2_journal_head 210 570 136 30 1 : tunables 32 16 8 : slabdata 19 19 128 : globalstat 115685
> 11086 3198 0 0 0 0 0 0 : cpustat 204408 10417 204798 9998
> 
> The problem then appears to be with the buffer heads associated with
> pages that have been recently written in data=journal mode are not
> getting freed.  I haven't had time to take this any further, but I
> wanted to document what I've found to date as a checkpoint.  If
> someone has time to take this further, or has any additional insight,
> I'd certainly appreciate it!
> 
> 							- Ted
> 
> P.S.  I will shortly be releasing an enhancement to kvm-xfstests and
> gce-xfstests which allows collapse/insert/zero range to be easily
> disabled, like this:
> 
> gce-xfstests --hooks /tmp/hooks  -C 20 -c data_journal --no-collapse --no-zero --no-insert generic/091
> 
> (The above traces were taken without --no-collapse --no-zero and
> --noinsert.  With those options added, the memory leak goes away.)

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