[Ksummit-discuss] [TOPIC] XArray

[Ksummit-discuss] [TOPIC] XArray

[Matthew Wilcox]

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Now that the XArray is in, it's time to make use of it. I've got a git tree
which converts every current user of the radix tree to the XArray as well
as converting some users of the IDA to the XArray.

The XArray may also be a great replacement for a list_head in your data
structure.

I can also talk about currently inappropriate uses for the XArray and what
I might do in future to make the XArray useful for more users.

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Re: [Ksummit-discuss] [TOPIC] XArray

[Theodore Y. Ts'o]

On Tue, Nov 13, 2018 at 10:02:13AM -0800, Matthew Wilcox wrote:
> Now that the XArray is in, it's time to make use of it. I've got a git tree
> which converts every current user of the radix tree to the XArray as well
> as converting some users of the IDA to the XArray.
> 
> The XArray may also be a great replacement for a list_head in your data
> structure.
> 
> I can also talk about currently inappropriate uses for the XArray and what
> I might do in future to make the XArray useful for more users.

This has been scheduled for Wednesday at 4pm.

     	      		    	      	 - Ted
x

Re: [Ksummit-discuss] [TOPIC] XArray

[Linus Walleij]

On Tue, Nov 13, 2018 at 7:02 PM Matthew Wilcox <willy6545@gmail.com> wrote:

> Now that the XArray is in, it's time to make use of it. I've got a git tree which converts
> every current user of the radix tree to the XArray as well as converting some
> users of the IDA to the XArray.
>
> The XArray may also be a great replacement for a list_head in your data structure.
>
> I can also talk about currently inappropriate uses for the XArray and what I
> might do in future to make the XArray useful for more users.

This sounds like awesome.

I hope there will be an LWN article coming out of this for those of us
who cannot participate in person.

Yours,
Linus Walleij

Re: [Ksummit-discuss] [TOPIC] XArray

[Theodore Y. Ts'o]

On Wed, Nov 14, 2018 at 11:02:54AM +0100, Linus Walleij wrote:
> > Now that the XArray is in, it's time to make use of it. I've got a git tree which converts
> > every current user of the radix tree to the XArray as well as converting some
> > users of the IDA to the XArray.
> >
> > The XArray may also be a great replacement for a list_head in your data structure.
> >
> > I can also talk about currently inappropriate uses for the XArray and what I
> > might do in future to make the XArray useful for more users.
> 
> This sounds like awesome.
> 
> I hope there will be an LWN article coming out of this for those of us
> who cannot participate in person.

It will video taped and should be available on the Linux Plumber's
Conference You Tube channel by next week, perhaps sooner.

   	      	    	       	  	       	   - Ted

Re: [Ksummit-discuss] [TOPIC] XArray

[Jonathan Corbet]

On Wed, 14 Nov 2018 11:02:54 +0100
Linus Walleij <linus.walleij@linaro.org> wrote:

> > The XArray may also be a great replacement for a list_head in your data structure.
> >
> > I can also talk about currently inappropriate uses for the XArray and what I
> > might do in future to make the XArray useful for more users.  
> 
> This sounds like awesome.
> 
> I hope there will be an LWN article coming out of this for those of us
> who cannot participate in person.

Just FWIW, I was there, but I suspect I'll not be making an article out
of it; quite a bit of the material was stuff that we've covered before.
The video should be available in a week or two for those who want to
catch up on the rest.

Thanks,

jon

Re: [Ksummit-discuss] [TOPIC] XArray

[Theodore Y. Ts'o]

On Thu, Nov 15, 2018 at 04:03:02PM -0700, Jonathan Corbet wrote:
> 
> Just FWIW, I was there, but I suspect I'll not be making an article out
> of it; quite a bit of the material was stuff that we've covered before.
> The video should be available in a week or two for those who want to
> catch up on the rest.

A good chunk of the contents of Matthew's talk can be found at:

https://lwn.net/Articles/745073/
https://www.kernel.org/doc/html/latest/core-api/xarray.html

Two important things that's not covered in these two links are:

1)  Some future plans that Matthew has for making XArray even better

2)  The use cases for which XArray is not (yet) ready.

Short version: Sparse arrays, hash tables, and other things where the
breadth of the keyspace that gets used is very wide relative to the
number of elements stored in the XArray.  So if you need to store two
elements, one where the key is 0x0000000 and the other key is
0xffffff00, XArray might not be the best choice for you --- but maybe
that answer will change in a year or so --- see (1) above.

For more details, the video and slides should be available soon.  :-)

Cheers,

    	 	      	    	      		- Ted

Re: [Ksummit-discuss] [TOPIC] XArray

[Matthew Wilcox]

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Thanks, Ted, that's a pretty accurate summary.

I'd say previous talks have been aimed at getting feedback on the API (and
several of the changes to the API came from giving those talks).  This talk
was "It's been merged, you should consider using it, here's why you might
want to"

Slides here:
http://www.infradead.org/~willy/linux/Plumbers2018XArray.pdf


On Thu, Nov 15, 2018 at 10:23 PM Theodore Y. Ts'o <tytso@mit.edu> wrote:

> On Thu, Nov 15, 2018 at 04:03:02PM -0700, Jonathan Corbet wrote:
> >
> > Just FWIW, I was there, but I suspect I'll not be making an article out
> > of it; quite a bit of the material was stuff that we've covered before.
> > The video should be available in a week or two for those who want to
> > catch up on the rest.
>
> A good chunk of the contents of Matthew's talk can be found at:
>
> https://lwn.net/Articles/745073/
> https://www.kernel.org/doc/html/latest/core-api/xarray.html
>
> Two important things that's not covered in these two links are:
>
> 1)  Some future plans that Matthew has for making XArray even better
>
> 2)  The use cases for which XArray is not (yet) ready.
>
> Short version: Sparse arrays, hash tables, and other things where the
> breadth of the keyspace that gets used is very wide relative to the
> number of elements stored in the XArray.  So if you need to store two
> elements, one where the key is 0x0000000 and the other key is
> 0xffffff00, XArray might not be the best choice for you --- but maybe
> that answer will change in a year or so --- see (1) above.
>
> For more details, the video and slides should be available soon.  :-)
>
> Cheers,
>
>                                                 - Ted
> _______________________________________________
> Ksummit-discuss mailing list
> Ksummit-discuss@lists.linuxfoundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/ksummit-discuss
>

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Re: [Ksummit-discuss] [TOPIC] XArray

[William Kucharski]

> On Nov 13, 2018, at 11:02 AM, Matthew Wilcox <willy6545@gmail.com> wrote:
> 
> Now that the XArray is in, it's time to make use of it. I've got a git tree which converts every current user of the radix tree to the XArray as well as converting some users of the IDA to the XArray.
> 
> The XArray may also be a great replacement for a list_head in your data structure.
> 
> I can also talk about currently inappropriate uses for the XArray and what I might do in future to make the XArray useful for more users.

I hope you'll also cover multi-order usage, e.g. for huge page size support in the page cache.

Thanks!
    -- Bill

Re: [Ksummit-discuss] [TOPIC] XArray

[Matthew Wilcox]

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I decided to leave that out of today's talk (in this timeslot; it was
briefly discussed in Christoph & Mike's hugepage slot during the
performance miniconf).

I should have patches soon to implement that -- the problem is not on the
XArray side, but on the page cache side. Unless there's a bug, of course,
and DAX is the canary in the coal-mine here.

On Wed., Nov. 14, 2018, 15:46 William Kucharski <
william.kucharski@oracle.com wrote:

>
>
> > On Nov 13, 2018, at 11:02 AM, Matthew Wilcox <willy6545@gmail.com>
> wrote:
> >
> > Now that the XArray is in, it's time to make use of it. I've got a git
> tree which converts every current user of the radix tree to the XArray as
> well as converting some users of the IDA to the XArray.
> >
> > The XArray may also be a great replacement for a list_head in your data
> structure.
> >
> > I can also talk about currently inappropriate uses for the XArray and
> what I might do in future to make the XArray useful for more users.
>
> I hope you'll also cover multi-order usage, e.g. for huge page size
> support in the page cache.
>
> Thanks!
>     -- Bill

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