Patchwork ext4: optimize extent selection for block removal in case of hole punch

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Submitter Ashish Sangwan
Date May 24, 2013, 2:39 p.m.
Message ID <519f7ba2.04fc440a.06c2.ffffd589@mx.google.com>
Download mbox | patch
Permalink /patch/246182/
State New
Headers show

Comments

Ashish Sangwan - May 24, 2013, 2:39 p.m.
From: Ashish Sangwan <a.sangwan@samsung.com>

Both hole punch and truncate use ext4_ext_rm_leaf for removing
blocks. Currently we choose the last extent as the starting
point for removing blocks: ex = EXT_LAST_EXTENT(eh);
This is OK for truncate but for hole punch we can optimize the
extent selection as the path is already initialized.
We could use this information to select proper starting extent.
The code change in this patch will not affect truncate as for
truncate path[depth].p_ext will always be NULL.

Signed-off-by: Ashish Sangwan <a.sangwan@samsung.com>
Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
---
 fs/ext4/extents.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)
Theodore Ts'o - June 18, 2013, 3:40 p.m.
On Fri, May 24, 2013 at 08:09:17PM +0530, ashishsangwan2@gmail.com wrote:
> From: Ashish Sangwan <a.sangwan@samsung.com>
> 
> Both hole punch and truncate use ext4_ext_rm_leaf for removing
> blocks. Currently we choose the last extent as the starting
> point for removing blocks: ex = EXT_LAST_EXTENT(eh);
> This is OK for truncate but for hole punch we can optimize the
> extent selection as the path is already initialized.
> We could use this information to select proper starting extent.
> The code change in this patch will not affect truncate as for
> truncate path[depth].p_ext will always be NULL.
> 
> Signed-off-by: Ashish Sangwan <a.sangwan@samsung.com>
> Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>

Applied, thanks.

					- Ted
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Ashish Sangwan - June 19, 2013, 1:45 p.m.
On Tue, Jun 18, 2013 at 9:10 PM, Theodore Ts'o <tytso@mit.edu> wrote:
> On Fri, May 24, 2013 at 08:09:17PM +0530, ashishsangwan2@gmail.com wrote:
>> From: Ashish Sangwan <a.sangwan@samsung.com>
>>
>> Both hole punch and truncate use ext4_ext_rm_leaf for removing
>> blocks. Currently we choose the last extent as the starting
>> point for removing blocks: ex = EXT_LAST_EXTENT(eh);
>> This is OK for truncate but for hole punch we can optimize the
>> extent selection as the path is already initialized.
>> We could use this information to select proper starting extent.
>> The code change in this patch will not affect truncate as for
>> truncate path[depth].p_ext will always be NULL.
>>
>> Signed-off-by: Ashish Sangwan <a.sangwan@samsung.com>
>> Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
>
> Applied, thanks.
Hi Ted,

Sorry I cannot see the patch changes in ext4 dev branch.

Regards,
Ashish
>
>                                         - Ted
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Theodore Ts'o - June 19, 2013, 2:06 p.m.
On Wed, Jun 19, 2013 at 07:15:35PM +0530, Ashish Sangwan wrote:
> On Tue, Jun 18, 2013 at 9:10 PM, Theodore Ts'o <tytso@mit.edu> wrote:
> > On Fri, May 24, 2013 at 08:09:17PM +0530, ashishsangwan2@gmail.com wrote:
> >> From: Ashish Sangwan <a.sangwan@samsung.com>
> >>
> >> Both hole punch and truncate use ext4_ext_rm_leaf for removing
> >> blocks. Currently we choose the last extent as the starting
> >> point for removing blocks: ex = EXT_LAST_EXTENT(eh);
> >> This is OK for truncate but for hole punch we can optimize the
> >> extent selection as the path is already initialized.
> >> We could use this information to select proper starting extent.
> >> The code change in this patch will not affect truncate as for
> >> truncate path[depth].p_ext will always be NULL.
> >>
> >> Signed-off-by: Ashish Sangwan <a.sangwan@samsung.com>
> >> Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
> >
> > Applied, thanks.
> 
> Sorry I cannot see the patch changes in ext4 dev branch.

Sorry, I dropped this patch from the dev branch last night, but I
didn't want to send e-mail about it until I had completed enough
testing to be sure.  It appears that this patch is causing a
regression; xfstests generic/269 and generic/279 to fail in the
nojournal configuration.

The tests are ones which have multiple fsstress threads racing with
dd/ENOSPC hitters, with (#270) and without (#269) quota enabled.  It's
not at all obvious to me why your particular change would make a
difference here, and it may simply be that your optimization is
exposing a timing change and is not the root cause of the failure, but
I'm going to move this to the unstable portion of the patch series
until we do further investigation.

If you could take a look at this, I would appreciate it, but as I
said, this may very well turn out not be the fault of your patch.

Regards,

						- Ted

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Ashish Sangwan - June 19, 2013, 3:44 p.m.
On Wed, Jun 19, 2013 at 7:36 PM, Theodore Ts'o <tytso@mit.edu> wrote:
> On Wed, Jun 19, 2013 at 07:15:35PM +0530, Ashish Sangwan wrote:
>> On Tue, Jun 18, 2013 at 9:10 PM, Theodore Ts'o <tytso@mit.edu> wrote:
>> > On Fri, May 24, 2013 at 08:09:17PM +0530, ashishsangwan2@gmail.com wrote:
>> >> From: Ashish Sangwan <a.sangwan@samsung.com>
>> >>
>> >> Both hole punch and truncate use ext4_ext_rm_leaf for removing
>> >> blocks. Currently we choose the last extent as the starting
>> >> point for removing blocks: ex = EXT_LAST_EXTENT(eh);
>> >> This is OK for truncate but for hole punch we can optimize the
>> >> extent selection as the path is already initialized.
>> >> We could use this information to select proper starting extent.
>> >> The code change in this patch will not affect truncate as for
>> >> truncate path[depth].p_ext will always be NULL.
>> >>
>> >> Signed-off-by: Ashish Sangwan <a.sangwan@samsung.com>
>> >> Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
>> >
>> > Applied, thanks.
>>
>> Sorry I cannot see the patch changes in ext4 dev branch.
>
> Sorry, I dropped this patch from the dev branch last night, but I
> didn't want to send e-mail about it until I had completed enough
> testing to be sure.  It appears that this patch is causing a
> regression; xfstests generic/269 and generic/279 to fail in the
> nojournal configuration.
>
Dropping this patch makes sense until root cause is not obvious.

> The tests are ones which have multiple fsstress threads racing with
> dd/ENOSPC hitters, with (#270) and without (#269) quota enabled.  It's
> not at all obvious to me why your particular change would make a
> difference here, and it may simply be that your optimization is
> exposing a timing change and is not the root cause of the failure, but
> I'm going to move this to the unstable portion of the patch series
> until we do further investigation.
>
> If you could take a look at this, I would appreciate it, but as I
> said, this may very well turn out not be the fault of your patch.
>
Sure, I will try looking into it.

Regards,
Ashish
> Regards,
>
>                                                 - Ted
>
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Theodore Ts'o - June 23, 2013, 6:43 p.m.
Lukas's patch: "ext4: only zero partial blocks in
ext4_zero_partial_blocks()" appears to address the failures I was
seeing with xfstests 269 and 270, so I'm going to add this patch back
to the ext4 git tree.

Regards,

					- Ted
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Patch

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 3676dae..7c1a5d3 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -2490,7 +2490,9 @@  ext4_ext_rm_leaf(handle_t *handle, struct inode *inode,
 		return -EIO;
 	}
 	/* find where to start removing */
-	ex = EXT_LAST_EXTENT(eh);
+	ex = path[depth].p_ext;
+	if (!ex)
+		ex = EXT_LAST_EXTENT(eh);
 
 	ex_ee_block = le32_to_cpu(ex->ee_block);
 	ex_ee_len = ext4_ext_get_actual_len(ex);