Some information about direct-io support on ubifs

Some information about direct-io support on ubifs

[Michael Nazzareno Trimarchi]

Hi all

I would like to have some information on how to implement direct-io
support in ubifs. I have tried to mount squashfs image as file in
ubifs using loopback and direct-io but it seems that loop can not
handle when this is on top of ubifs. From what I understand from the
code it seems that the requirement is that the direct-io is
implemented in the filesystem where the file is stored. I have
simulated using nand sim. The idea is to reduce the buffering. I'm
open to have other suggestions regarding this too.

Michael

______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/

Re: Some information about direct-io support on ubifs

[Zhihao Cheng]

在 2024/11/11 17:37, Michael Nazzareno Trimarchi 写道:
> Hi all
> 
> I would like to have some information on how to implement direct-io
> support in ubifs. I have tried to mount squashfs image as file in
> ubifs using loopback and direct-io but it seems that loop can not
> handle when this is on top of ubifs. From what I understand from the
> code it seems that the requirement is that the direct-io is
> implemented in the filesystem where the file is stored. I have
> simulated using nand sim. The idea is to reduce the buffering. I'm
> open to have other suggestions regarding this too.
> 
> Michael
> .
> 
Hi Michael,
There is a discussion(9 years ago) about ubifs dio[1], of course we 
cannot implement it as a fake interface now.
Before talking about adding dio support for UBIFS, let me know some 
background information. What's the purpose of using dio for opening 
squashfs image file? What's the goal of reducing buffer you mentioned 
above, Better performance? Less memory usage?


[1] 
https://lore.kernel.org/lkml/1440016553-26481-2-git-send-email-richard@nod.at/

______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/

Re: Some information about direct-io support on ubifs

[Michael Nazzareno Trimarchi]

Hi

On Mon, Nov 11, 2024 at 3:15 PM Zhihao Cheng <chengzhihao1@huawei.com> wrote:
>
> 在 2024/11/11 17:37, Michael Nazzareno Trimarchi 写道:
> > Hi all
> >
> > I would like to have some information on how to implement direct-io
> > support in ubifs. I have tried to mount squashfs image as file in
> > ubifs using loopback and direct-io but it seems that loop can not
> > handle when this is on top of ubifs. From what I understand from the
> > code it seems that the requirement is that the direct-io is
> > implemented in the filesystem where the file is stored. I have
> > simulated using nand sim. The idea is to reduce the buffering. I'm
> > open to have other suggestions regarding this too.
> >
> > Michael
> > .
> >
> Hi Michael,
> There is a discussion(9 years ago) about ubifs dio[1], of course we
> cannot implement it as a fake interface now.
> Before talking about adding dio support for UBIFS, let me know some
> background information. What's the purpose of using dio for opening
> squashfs image file? What's the goal of reducing buffer you mentioned
> above, Better performance? Less memory usage?
>
>
> [1]
> https://lore.kernel.org/lkml/1440016553-26481-2-git-send-email-richard@nod.at/


The goal is less memory usage. Each squashfs is mounted using loopback
device, so according
to some thread on direct-io, I understand that we then not have
buffering two times on ubifs level and loop
level, but the thread was not clear to me. The device has very limited
capability and memory. I have done some
test with fuse  but I did not have numbers to compare them


Michael

______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/

Re: Some information about direct-io support on ubifs

[Zhihao Cheng]

在 2024/11/11 23:08, Michael Nazzareno Trimarchi 写道:
> Hi
> 
> On Mon, Nov 11, 2024 at 3:15 PM Zhihao Cheng <chengzhihao1@huawei.com> wrote:
>>
>> 在 2024/11/11 17:37, Michael Nazzareno Trimarchi 写道:
>>> Hi all
>>>
>>> I would like to have some information on how to implement direct-io
>>> support in ubifs. I have tried to mount squashfs image as file in
>>> ubifs using loopback and direct-io but it seems that loop can not
>>> handle when this is on top of ubifs. From what I understand from the
>>> code it seems that the requirement is that the direct-io is
>>> implemented in the filesystem where the file is stored. I have
>>> simulated using nand sim. The idea is to reduce the buffering. I'm
>>> open to have other suggestions regarding this too.
>>>
>>> Michael
>>> .
>>>
>> Hi Michael,
>> There is a discussion(9 years ago) about ubifs dio[1], of course we
>> cannot implement it as a fake interface now.
>> Before talking about adding dio support for UBIFS, let me know some
>> background information. What's the purpose of using dio for opening
>> squashfs image file? What's the goal of reducing buffer you mentioned
>> above, Better performance? Less memory usage?
>>
>>
>> [1]
>> https://lore.kernel.org/lkml/1440016553-26481-2-git-send-email-richard@nod.at/
> 
> 
> The goal is less memory usage. Each squashfs is mounted using loopback
> device, so according
> to some thread on direct-io, I understand that we then not have
> buffering two times on ubifs level and loop
> level, but the thread was not clear to me. The device has very limited
> capability and memory. I have done some
> test with fuse  but I did not have numbers to compare them
> 

Hi Michael,

I think it is possible to support DIO for UBIFS in theory, but it is not 
an easy task. We need to imeplement read/write functions, and we should 
iterate user data bytes by UBIFS_BLOCK_SIZE unit.
1. Things should be done in write function:
    1) Do space reservation, refer to ubifs_write_begin -> 
allocate_budget, of cource the origin 'req.new_page' cannot be used and 
we should define a new budget type based on UBIFS_BLOCK_SIZE.
    2) record user data in data node, refer to do_writepage -> 
ubifs_jnl_write_data
    3) invalidate page cache after io complete, refer to dio_complete -> 
kiocb_invalidate_post_direct_write
    4) release budget, refer to do_writepage -> 
release_new_page_budget/release_existing_page_budget
2. Things should be done in read function:
    1) sync page cache data to disk, make sure that dio reading get the 
latest user data, refer to __blockdev_direct_IO -> 
filemap_write_and_wait_range
    2) read data from UHIFS, refer to do_readpage -> read_block
Maybe there are many trivial details during developing.
> 
> Michael
> .
> 


______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/

Re: Some information about direct-io support on ubifs

[Michael Nazzareno Trimarchi]

Hi

On Thu, Nov 14, 2024 at 3:10 PM Zhihao Cheng <chengzhihao1@huawei.com> wrote:
>
> 在 2024/11/11 23:08, Michael Nazzareno Trimarchi 写道:
> > Hi
> >
> > On Mon, Nov 11, 2024 at 3:15 PM Zhihao Cheng <chengzhihao1@huawei.com> wrote:
> >>
> >> 在 2024/11/11 17:37, Michael Nazzareno Trimarchi 写道:
> >>> Hi all
> >>>

First of all, thank you very much.

> >>> I would like to have some information on how to implement direct-io
> >>> support in ubifs. I have tried to mount squashfs image as file in
> >>> ubifs using loopback and direct-io but it seems that loop can not
> >>> handle when this is on top of ubifs. From what I understand from the
> >>> code it seems that the requirement is that the direct-io is
> >>> implemented in the filesystem where the file is stored. I have
> >>> simulated using nand sim. The idea is to reduce the buffering. I'm
> >>> open to have other suggestions regarding this too.
> >>>
> >>> Michael
> >>> .
> >>>
> >> Hi Michael,
> >> There is a discussion(9 years ago) about ubifs dio[1], of course we
> >> cannot implement it as a fake interface now.
> >> Before talking about adding dio support for UBIFS, let me know some
> >> background information. What's the purpose of using dio for opening
> >> squashfs image file? What's the goal of reducing buffer you mentioned
> >> above, Better performance? Less memory usage?
> >>
> >>
> >> [1]
> >> https://lore.kernel.org/lkml/1440016553-26481-2-git-send-email-richard@nod.at/
> >
> >
> > The goal is less memory usage. Each squashfs is mounted using loopback
> > device, so according
> > to some thread on direct-io, I understand that we then not have
> > buffering two times on ubifs level and loop
> > level, but the thread was not clear to me. The device has very limited
> > capability and memory. I have done some
> > test with fuse  but I did not have numbers to compare them
> >
>
> Hi Michael,
>
> I think it is possible to support DIO for UBIFS in theory, but it is not
> an easy task. We need to imeplement read/write functions, and we should
> iterate user data bytes by UBIFS_BLOCK_SIZE unit.
> 1. Things should be done in write function:
>     1) Do space reservation, refer to ubifs_write_begin ->
> allocate_budget, of cource the origin 'req.new_page' cannot be used and
> we should define a new budget type based on UBIFS_BLOCK_SIZE.

I have seen that allocate a budget using an allocated request. Here you mean
to change the interface a bit to require the allocated budget that
must be multiple of BLOCK_SIZE?

If the question looks silly, sorry for that.

>     2) record user data in data node, refer to do_writepage ->
> ubifs_jnl_write_data
>     3) invalidate page cache after io complete, refer to dio_complete ->
> kiocb_invalidate_post_direct_write
>     4) release budget, refer to do_writepage ->
> release_new_page_budget/release_existing_page_budget

Ok. Let me give myself a few days to study.

> 2. Things should be done in read function:
>     1) sync page cache data to disk, make sure that dio reading get the
> latest user data, refer to __blockdev_direct_IO ->
> filemap_write_and_wait_range
>     2) read data from UHIFS, refer to do_readpage -> read_block
> Maybe there are many trivial details during developing.

Here the nice thing is to know how you test at the moment the ubifs and easy way
to development it.

Michael

> >
> > Michael
> > .
> >
>


-- 
Michael Nazzareno Trimarchi
Co-Founder & Chief Executive Officer
M. +39 347 913 2170
michael@amarulasolutions.com
__________________________________

Amarula Solutions BV
Joop Geesinkweg 125, 1114 AB, Amsterdam, NL
T. +31 (0)85 111 9172
info@amarulasolutions.com
www.amarulasolutions.com

______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/

Re: Some information about direct-io support on ubifs

[Richard Weinberger]

----- Ursprüngliche Mail -----
> Von: "Michael Nazzareno Trimarchi" <michael@amarulasolutions.com>
>> >>> I would like to have some information on how to implement direct-io
>> >>> support in ubifs. I have tried to mount squashfs image as file in
>> >>> ubifs using loopback and direct-io but it seems that loop can not
>> >>> handle when this is on top of ubifs. From what I understand from the
>> >>> code it seems that the requirement is that the direct-io is
>> >>> implemented in the filesystem where the file is stored. I have
>> >>> simulated using nand sim. The idea is to reduce the buffering. I'm
>> >>> open to have other suggestions regarding this too.

Why are you using UBIFS anyway for this? Just place the squashfs inside
an UBI volume.

Thanks,
//richard

______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/

Re: Some information about direct-io support on ubifs

[Michael Nazzareno Trimarchi]

Hi Richard

On Mon, Nov 18, 2024 at 11:02 AM Richard Weinberger <richard@nod.at> wrote:
>
> ----- Ursprüngliche Mail -----
> > Von: "Michael Nazzareno Trimarchi" <michael@amarulasolutions.com>
> >> >>> I would like to have some information on how to implement direct-io
> >> >>> support in ubifs. I have tried to mount squashfs image as file in
> >> >>> ubifs using loopback and direct-io but it seems that loop can not
> >> >>> handle when this is on top of ubifs. From what I understand from the
> >> >>> code it seems that the requirement is that the direct-io is
> >> >>> implemented in the filesystem where the file is stored. I have
> >> >>> simulated using nand sim. The idea is to reduce the buffering. I'm
> >> >>> open to have other suggestions regarding this too.
>
> Why are you using UBIFS anyway for this? Just place the squashfs inside
> an UBI volume.

Yes this is one of the solutions I have proposed, but the idea is to
update a single squashfs
container and not bound the limit in the beginning of the device life.
Does it make sense to you?

<rootfs ubifs> you can create any size/number of containers if they
fit inside the device.

Michael

>
> Thanks,
> //richard



-- 
Michael Nazzareno Trimarchi
Co-Founder & Chief Executive Officer
M. +39 347 913 2170
michael@amarulasolutions.com
__________________________________

Amarula Solutions BV
Joop Geesinkweg 125, 1114 AB, Amsterdam, NL
T. +31 (0)85 111 9172
info@amarulasolutions.com
www.amarulasolutions.com

______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/

Re: Some information about direct-io support on ubifs

[Richard Weinberger]

----- Ursprüngliche Mail -----
> Von: "Michael Nazzareno Trimarchi" <michael@amarulasolutions.com>
>> Why are you using UBIFS anyway for this? Just place the squashfs inside
>> an UBI volume.
> 
> Yes this is one of the solutions I have proposed, but the idea is to
> update a single squashfs
> container and not bound the limit in the beginning of the device life.
> Does it make sense to you?

Not really because you can add/resize UBI volumes at runtime.
So, let UBI be the container.

You can eben give them names.

Thanks,
//richard

______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/