Re: backing up ext4 fs, system unresponsive, thrashing like crazy even though swap is unused

Re: backing up ext4 fs, system unresponsive, thrashing like crazy even though swap is unused

[Dimitrios Apostolou]

On Sun, 2012-11-25 at 15:55 +0200, Dimitrios Apostolou wrote:
> on an old PIII-500MHz laptop, 128MB RAM, kernel 3.6.6, I started a
> backup process (tar|xz -4, nice'd and ionice'd -c3) from ext4 on local
> ATA disk to ext3 on external USB disk (USB-2.0 port on PCMCIA card).
> Even though earlier system load was minimal, free memory was plenty, the
> system now is unresponsive and is thrashing the disk, but the swapfile
> is rarely touched.

I'm now having the same experience even though I replaced xz (which
needed ~50MB RAM) with gzip. Even though I feel the realtime root shell
is a bit more responsive than before, the OOM killer is out killing 
small processes like syslog-ng and systemd-logind... The
ext4_inode_cache slab is taking almost all my memory (117MB). Please
advise!


Thanks,
Dimitris

kmemleak failure (was Re: backing up ext4 fs, system unresponsive, thrashing like crazy even though swap is unused)

[Dimitrios Apostolou]

Hello,

I tried running a kmemleak and DEBUG_SLUB enabled kernel, but almost
within 5 minutes of starting the backup process, I got:

[  486.863124] kmemleak: Cannot allocate a kmemleak_object structure
[  486.887195] kmemleak: Automatic memory scanning thread ended
[  486.906604] kmemleak: Kernel memory leak detector disabled


Any ideas?

Thanks,
Dimitris

Re: backing up ext4 fs, system unresponsive, thrashing like crazy even though swap is unused

[Roland Eggner]

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On 2012-11-25 Sunday at 21:30 +0200 Dimitrios Apostolou wrote:
> On Sun, 2012-11-25 at 15:55 +0200, Dimitrios Apostolou wrote:
> > on an old PIII-500MHz laptop, 128MB RAM, kernel 3.6.6, I started a
> > backup process (tar|xz -4, nice'd and ionice'd -c3) from ext4 on local
> > ATA disk to ext3 on external USB disk (USB-2.0 port on PCMCIA card).
> > Even though earlier system load was minimal, free memory was plenty, the
> > system now is unresponsive and is thrashing the disk, but the swapfile
> > is rarely touched.
> 
> I'm now having the same experience even though I replaced xz (which
> needed ~50MB RAM) with gzip. Even though I feel the realtime root shell
> is a bit more responsive than before, the OOM killer is out killing 
> small processes like syslog-ng and systemd-logind... The
> ext4_inode_cache slab is taking almost all my memory (117MB). Please
> advise!

Hello Dimitrios,

I would try a 2.6.27.* kernel, for following reasons:

(1)  Kernel development since 2.6.27 achieved significant performance 
improvements at the cost of exploding memory consumption by the kernel for 
_internal_  data structures.  I am currently using a 3.2.34 kernel on a Notebook 
with 4 G RAM.  0,5 … 1 G RAM is usually occupied just by kernel slab [1];  this 
memory cannot be swapped, it cannot be released by other means than rebooting, 
and there seems to be  _no_  adjustment to memory pressure.  I am surprised, 
that you have managed to boot a 3.6.* kernel at all with only 128 M RAM.

(2)  At the time, when I used a PIII-Notebook, kernels 2.6.27 to 2.6.29 where 
current.  Thus chances are good, that a 2.6.27.* kernel will support chipset, 
PCI bus and devices of your notebook.  2.6.27 got longterm maintainance, the 
latest release in the linux-stable git repository is 2.6.27.62.
So Q @ LKML community:
Does anybody know a x86 distribution or live-CD using a 2.6.27.* kernel?


[1]  Picture described in my LKML message
Date:  Fri, 20 Jan 2012 01:08:00 +0100
Subject:  Re: [kmemleak report 1/2] kernel 3.1.6, x86_64: mm, xfs ?, vfs ?
remained the same with  _every_  3.1.* and 3.2.* kernel tried so far.


-- 
Roland

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Re: kmemleak failure (was Re: backing up ext4 fs, system unresponsive, thrashing like crazy even though swap is unused)

[Dimitrios Apostolou]

On Mon, 2012-11-26 at 00:41 +0200, Dimitrios Apostolou wrote:
> Hello,
> 
> I tried running a kmemleak and DEBUG_SLUB enabled kernel, but almost
> within 5 minutes of starting the backup process, I got:
> 
> [  486.863124] kmemleak: Cannot allocate a kmemleak_object structure
> [  486.887195] kmemleak: Automatic memory scanning thread ended
> [  486.906604] kmemleak: Kernel memory leak detector disabled

Important detail: I decided to try kmemleak after suspecting a leak
because 'echo 3>/proc/sys/vm/drop_caches' left about 90MB out of 118MB
of ext4_inode_cache, and I found no way to get rid of that (via
remounting filesystems for example).

Re: backing up ext4 fs, system unresponsive, thrashing like crazy even though swap is unused

[Alan Cox]

> Does anybody know a x86 distribution or live-CD using a 2.6.27.* kernel?

Probably not a good idea, there are known exploitable holes in 2.6.27 era
kernels and nobody maintains anything that old.

I guess RHEL/Centos might work for you.

I've not had any problems with leaks in 3.6 but there have been a few
reports and its clear that some obscure configurations trigger something
bad.

Gnome 3 on the other hand leaks like a sieve.

Re: backing up ext4 fs, system unresponsive, thrashing like crazy even though swap is unused

[Roland Eggner]

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On 2012-11-25 Sunday at 23:56 +0000 Alan Cox wrote:
> > Does anybody know a x86 distribution or live-CD using a 2.6.27.* kernel?
> 
> Probably not a good idea, there are known exploitable holes in 2.6.27 era
> kernels and nobody maintains anything that old.

“old” is relative …

cd git/linux-stable  && git log -1 --date=iso v2.6.27.62
........................................................
commit bc4e1a77b06519a01e7aed1125695598e27ddeb2
Author: Willy Tarreau <w@1wt.eu>
Date:   2012-03-17 14:03:53 +0100

    Linux 2.6.27.62

    Signed-off-by: Willy Tarreau <w@1wt.eu>


… and surely less exploitable than a system suffering oom-killer actions.

Google "linux-2.6.27 download" gives some Ubuntu hits …


> I guess RHEL/Centos might work for you.
>
> I've not had any problems with leaks in 3.6 but there have been a few
> reports and its clear that some obscure configurations trigger something
> bad.
> 
> Gnome 3 on the other hand leaks like a sieve.

For a system with 128 M total RAM, Gnome is obviously off topic.


-- 
Roland

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Re: backing up ext4 fs, system unresponsive, thrashing like crazy even though swap is unused

[Jan Kara]

On Sun 25-11-12 21:30:00, Dimitrios Apostolou wrote:
> On Sun, 2012-11-25 at 15:55 +0200, Dimitrios Apostolou wrote:
> > on an old PIII-500MHz laptop, 128MB RAM, kernel 3.6.6, I started a
> > backup process (tar|xz -4, nice'd and ionice'd -c3) from ext4 on local
> > ATA disk to ext3 on external USB disk (USB-2.0 port on PCMCIA card).
> > Even though earlier system load was minimal, free memory was plenty, the
> > system now is unresponsive and is thrashing the disk, but the swapfile
> > is rarely touched.
> 
> I'm now having the same experience even though I replaced xz (which
> needed ~50MB RAM) with gzip. Even though I feel the realtime root shell
> is a bit more responsive than before, the OOM killer is out killing 
> small processes like syslog-ng and systemd-logind... The
> ext4_inode_cache slab is taking almost all my memory (117MB). Please
> advise!
  Hmm, it seems commit 4eff96dd5283a102e0c1cac95247090be74a38ed might be
interesting for you. It landed in -stable kernels recently as well if I
remember right...

								Honza

-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR

Re: backing up ext4 fs, system unresponsive, thrashing like crazy even though swap is unused

[Dimitrios Apostolou]

On Thu, 6 Dec 2012, Jan Kara wrote:
> On Sun 25-11-12 21:30:00, Dimitrios Apostolou wrote:
>> On Sun, 2012-11-25 at 15:55 +0200, Dimitrios Apostolou wrote:
>>> on an old PIII-500MHz laptop, 128MB RAM, kernel 3.6.6, I started a
>>> backup process (tar|xz -4, nice'd and ionice'd -c3) from ext4 on local
>>> ATA disk to ext3 on external USB disk (USB-2.0 port on PCMCIA card).
>>> Even though earlier system load was minimal, free memory was plenty, the
>>> system now is unresponsive and is thrashing the disk, but the swapfile
>>> is rarely touched.
>>
>> I'm now having the same experience even though I replaced xz (which
>> needed ~50MB RAM) with gzip. Even though I feel the realtime root shell
>> is a bit more responsive than before, the OOM killer is out killing
>> small processes like syslog-ng and systemd-logind... The
>> ext4_inode_cache slab is taking almost all my memory (117MB). Please
>> advise!
>  Hmm, it seems commit 4eff96dd5283a102e0c1cac95247090be74a38ed might be
> interesting for you. It landed in -stable kernels recently as well if I
> remember right...

Thanks, I appreciate your help as I'm stuck in a dead end now, and I've 
been trying to write some debug hook that prints all ext4_inodes and the 
reason they are pinned (is there an easy way to find this out?).

So maybe there is a typo in the SHA1 sum you provided? Gitweb can't find 
it in Linus' tree.


Thanks,
Dimitris

Re: backing up ext4 fs, system unresponsive, thrashing like crazy even though swap is unused

[Jan Kara]

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On Thu 06-12-12 17:15:37, Dimitrios Apostolou wrote:
> On Thu, 6 Dec 2012, Jan Kara wrote:
> >On Sun 25-11-12 21:30:00, Dimitrios Apostolou wrote:
> >>On Sun, 2012-11-25 at 15:55 +0200, Dimitrios Apostolou wrote:
> >>>on an old PIII-500MHz laptop, 128MB RAM, kernel 3.6.6, I started a
> >>>backup process (tar|xz -4, nice'd and ionice'd -c3) from ext4 on local
> >>>ATA disk to ext3 on external USB disk (USB-2.0 port on PCMCIA card).
> >>>Even though earlier system load was minimal, free memory was plenty, the
> >>>system now is unresponsive and is thrashing the disk, but the swapfile
> >>>is rarely touched.
> >>
> >>I'm now having the same experience even though I replaced xz (which
> >>needed ~50MB RAM) with gzip. Even though I feel the realtime root shell
> >>is a bit more responsive than before, the OOM killer is out killing
> >>small processes like syslog-ng and systemd-logind... The
> >>ext4_inode_cache slab is taking almost all my memory (117MB). Please
> >>advise!
> > Hmm, it seems commit 4eff96dd5283a102e0c1cac95247090be74a38ed might be
> >interesting for you. It landed in -stable kernels recently as well if I
> >remember right...
> 
> Thanks, I appreciate your help as I'm stuck in a dead end now, and
> I've been trying to write some debug hook that prints all
> ext4_inodes and the reason they are pinned (is there an easy way to
> find this out?).
> 
> So maybe there is a typo in the SHA1 sum you provided? Gitweb can't
> find it in Linus' tree.
  Strange. You are right gitweb doesn't show the SHA1 but I can see it in
my git repo I pulled from Linus. Anyway, I've attached the fix for your
convenience.

								Honza

-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR

[-- Attachment #2: 0001-writeback-Put-unused-inodes-to-LRU-after-writeback-c.patch --]
[-- Type: text/x-patch, Size: 3356 bytes --]

>From 9501fee10d8594ab8ee7deb749fb48c1d3a7985e Mon Sep 17 00:00:00 2001
From: Jan Kara <jack@suse.cz>
Date: Mon, 19 Nov 2012 20:01:16 +0100
Subject: [PATCH v3] writeback: Put unused inodes to LRU after writeback completion

Commit 169ebd90 removed iget-iput pair from inode writeback. As a side effect,
inodes that are dirty during iput_final() call won't be ever added to inode LRU
(iput_final() doesn't add dirty inodes to LRU and later when the inode is
cleaned there's noone to add the inode there). Thus inodes are effectively
unreclaimable until someone looks them up again.

Practical effect of this bug is limited by the fact that inodes are
pinned by a dentry for long enough that the inode gets cleaned. But still
the bug can have nasty consequences leading up to OOM conditions under
certain circumstances. Following can easily reproduce the problem:

for (( i = 0; i < 1000; i++ )); do
  mkdir $i
  for (( j = 0; j < 1000; j++ )); do
    touch $i/$j
    echo 2 > /proc/sys/vm/drop_caches
  done
done

then one needs to run 'sync; ls -lR' to make inodes reclaimable again.

We fix the issue by inserting unused clean inodes into the LRU after writeback
finishes in inode_sync_complete().

CC: Al Viro <viro@zeniv.linux.org.uk>
CC: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
CC: stable@vger.kernel.org # >= 3.5
Reported-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/fs-writeback.c |    2 ++
 fs/inode.c        |   16 ++++++++++++++--
 fs/internal.h     |    1 +
 3 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 51ea267..3e3422f 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -228,6 +228,8 @@ static void requeue_io(struct inode *inode, struct bdi_writeback *wb)
 static void inode_sync_complete(struct inode *inode)
 {
 	inode->i_state &= ~I_SYNC;
+	/* If inode is clean an unused, put it into LRU now... */
+	inode_add_lru(inode);
 	/* Waiters must see I_SYNC cleared before being woken up */
 	smp_mb();
 	wake_up_bit(&inode->i_state, __I_SYNC);
diff --git a/fs/inode.c b/fs/inode.c
index b03c719..64999f1 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -408,6 +408,19 @@ static void inode_lru_list_add(struct inode *inode)
 	spin_unlock(&inode->i_sb->s_inode_lru_lock);
 }
 
+/*
+ * Add inode to LRU if needed (inode is unused and clean).
+ *
+ * Needs inode->i_lock held.
+ */
+void inode_add_lru(struct inode *inode)
+{
+	if (!(inode->i_state & (I_DIRTY | I_SYNC | I_FREEING | I_WILL_FREE)) &&
+	    !atomic_read(&inode->i_count) && inode->i_sb->s_flags & MS_ACTIVE)
+		inode_lru_list_add(inode);
+}
+
+
 static void inode_lru_list_del(struct inode *inode)
 {
 	spin_lock(&inode->i_sb->s_inode_lru_lock);
@@ -1390,8 +1403,7 @@ static void iput_final(struct inode *inode)
 
 	if (!drop && (sb->s_flags & MS_ACTIVE)) {
 		inode->i_state |= I_REFERENCED;
-		if (!(inode->i_state & (I_DIRTY|I_SYNC)))
-			inode_lru_list_add(inode);
+		inode_add_lru(inode);
 		spin_unlock(&inode->i_lock);
 		return;
 	}
diff --git a/fs/internal.h b/fs/internal.h
index 916b7cb..2f6af7f 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -110,6 +110,7 @@ extern int open_check_o_direct(struct file *f);
  * inode.c
  */
 extern spinlock_t inode_sb_list_lock;
+extern void inode_add_lru(struct inode *inode);
 
 /*
  * fs-writeback.c
-- 
1.7.1

Re: backing up ext4 fs, system unresponsive, thrashing like crazy even though swap is unused

[Dimitrios Apostolou]

Hi Jan, thanks for your help, with this commit I can't reproduce the 
problem. The problematic workload is no more inflating the 
ext4_inode_cache, in fact I've been able to run even heavier workloads 
with the ext4_inode_cache never surpassing 2-4MB.

Thanks everyone for helping,
Dimitris


On Thu, 6 Dec 2012, Jan Kara wrote:
> On Thu 06-12-12 17:15:37, Dimitrios Apostolou wrote:
>> On Thu, 6 Dec 2012, Jan Kara wrote:
>>> On Sun 25-11-12 21:30:00, Dimitrios Apostolou wrote:
>>>> On Sun, 2012-11-25 at 15:55 +0200, Dimitrios Apostolou wrote:
>>>>> on an old PIII-500MHz laptop, 128MB RAM, kernel 3.6.6, I started a
>>>>> backup process (tar|xz -4, nice'd and ionice'd -c3) from ext4 on local
>>>>> ATA disk to ext3 on external USB disk (USB-2.0 port on PCMCIA card).
>>>>> Even though earlier system load was minimal, free memory was plenty, the
>>>>> system now is unresponsive and is thrashing the disk, but the swapfile
>>>>> is rarely touched.
>>>>
>>>> I'm now having the same experience even though I replaced xz (which
>>>> needed ~50MB RAM) with gzip. Even though I feel the realtime root shell
>>>> is a bit more responsive than before, the OOM killer is out killing
>>>> small processes like syslog-ng and systemd-logind... The
>>>> ext4_inode_cache slab is taking almost all my memory (117MB). Please
>>>> advise!
>>> Hmm, it seems commit 4eff96dd5283a102e0c1cac95247090be74a38ed might be
>>> interesting for you. It landed in -stable kernels recently as well if I
>>> remember right...
>>
>> Thanks, I appreciate your help as I'm stuck in a dead end now, and
>> I've been trying to write some debug hook that prints all
>> ext4_inodes and the reason they are pinned (is there an easy way to
>> find this out?).
>>
>> So maybe there is a typo in the SHA1 sum you provided? Gitweb can't
>> find it in Linus' tree.
>  Strange. You are right gitweb doesn't show the SHA1 but I can see it in
> my git repo I pulled from Linus. Anyway, I've attached the fix for your
> convenience.
>
> 								Honza
>
> -- 
> Jan Kara <jack@suse.cz>
> SUSE Labs, CR
>