Bug 720918

Summary:	the block layer does't merge the requests sent from jbd/2.
Product:	Red Hat Enterprise Linux 6	Reporter:	Tao Ma <tm>
Component:	kernel	Assignee:	Jeff Moyer <jmoyer>
Status:	CLOSED ERRATA	QA Contact:	Petr Beňas <pbenas>
Severity:	medium	Docs Contact:
Priority:	unspecified
Version:	6.1	CC:	chellwig, dchinner, eguan, esandeen, jmoyer, lczerner, pbenas, pstehlik, rwheeler
Target Milestone:	rc
Target Release:	---
Hardware:	Unspecified
OS:	Linux
Whiteboard:
Fixed In Version:	kernel-2.6.32-206.el6	Doc Type:	Bug Fix
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2011-12-06 13:49:39 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:

Description Tao Ma 2011-07-13 08:45:32 UTC

Description of problem:
I check the blktrace from the journal commit, and it looks as if the request sent from the jbd2 isn't merged by the block layer although they are sequential write. Seems to be a bug in what jbd2 submit the bios.

Version-Release number of selected component (if applicable):

2.6.32-131.4.1

How reproducible:


Steps to Reproduce:
1. mkfs.ext4 -b 2048 /dev/sdx 10000000
2. sync
3. mount -t ext4 -o delalloc /dev/sdx /mnt/ext4
4. dd if=/dev/zero of=/mnt/ext4/a bs=1024K count=1
5. blktrace -a issue -a complete /dev/sdx -o -|blkparse -i -
  
Actual results:

  8,0    6       18     0.016058423  3342  D   W 461101317 + 4 [jbd2/sda11-8]
  8,0    6       19     0.016065473  3342  D   W 461101321 + 4 [jbd2/sda11-8]
  8,0    6       20     0.016070751  3342  D   W 461101325 + 4 [jbd2/sda11-8]
  8,0    6       21     0.016076180  3342  D   W 461101329 + 4 [jbd2/sda11-8]
  8,0    6       22     0.016081255  3342  D   W 461101333 + 4 [jbd2/sda11-8]
  8,0    6       23     0.016085963  3342  D   W 461101337 + 4 [jbd2/sda11-8]
  8,0    6       24     0.016182048     0  C   W 461101317 + 4 [0]
  8,0    6       25     0.016190820     0  C   W 461101325 + 4 [0]
  8,0    6       26     0.016193927     0  C   W 461101321 + 4 [0]
  8,0    6       27     0.016196532     0  C   W 461101333 + 4 [0]
  8,0    6       28     0.016199180     0  C   W 461101337 + 4 [0]
  8,0    6       29     0.016206180     0  C   W 461101329 + 4 [0]


Expected results:

  8,0    4       23     4.320315739  3129  D   W 461101317 + 24 [jbd2/sda11-8]
  8,0    4       24     4.320364518     0  C   W 461101317 + 24 [0]

Additional info:
In upstream commit 749ef9f8423, we use WRITE_SYNC instead of WRITE in
journal_commit_transaction. It causes a much heavy burden for
the disk as now the seqenctial write can't be merged(see the blktrace below).

Given the description of that commit 749ef9f8423, the reason why
we use WRITE_SYNC is that it wants to use REQ_NOIDLE and WRITE_SYNC_PLUG
also has that flag, so use WRITE_SYNC_PLUG instead. 

A corresponding fix has been sent to linux-ext4.
http://marc.info/?l=linux-ext4&m=131046746420316&w=2

Comment 2 Tao Ma 2011-07-22 07:00:53 UTC

hi, any update for this? Do you guys think this is a bug or not?

Comment 3 Jeff Moyer 2011-07-25 13:00:57 UTC

Hi, Tao,

I will look into this further for RHEL 6.3.  From our discussion upstream, my guess is your patch will go in as is, but I won't know for sure until I've done some more testing.

Thanks for reporting the problem and providing a fix!

Comment 4 Tao Ma 2011-07-25 14:49:58 UTC

Hi Jeffrey,
Thanks for the update. Please let me know when the patch is OK with your test so that I can track it in our production system.

Comment 6 Tao Ma 2011-09-06 08:10:52 UTC

Hi Jeffrey,
   I just noticed that the status is changed to POST. So would you mind attaching the patch here? Thanks.

Comment 7 RHEL Program Management 2011-09-07 14:20:10 UTC

This request was evaluated by Red Hat Product Management for inclusion
in a Red Hat Enterprise Linux maintenance release. Product Management has 
requested further review of this request by Red Hat Engineering, for potential
inclusion in a Red Hat Enterprise Linux Update release for currently deployed 
products. This request is not yet committed for inclusion in an Update release.

Comment 8 Aristeu Rozanski 2011-10-05 15:32:52 UTC

Patch(es) available on kernel-2.6.32-206.el6

Comment 13 Petr Beňas 2011-10-06 14:55:49 UTC

Reproduced in 2.6.32-131.4.1.el6.x86_64 and 2.6.32-178.el6.x86_64, unable to reproduce in 2.6.32-205.el6.x86_64 and verified in 2.6.32-206.el6.x86_64.

Comment 14 errata-xmlrpc 2011-12-06 13:49:39 UTC

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

http://rhn.redhat.com/errata/RHSA-2011-1530.html