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Re: [Qemu-devel] [PATCH v19 3/7] xbitmap: add more operations
From: |
Matthew Wilcox |
Subject: |
Re: [Qemu-devel] [PATCH v19 3/7] xbitmap: add more operations |
Date: |
Sun, 17 Dec 2017 14:18:42 -0800 |
User-agent: |
Mutt/1.9.1 (2017-09-22) |
On Sun, Dec 17, 2017 at 01:47:21PM +0000, Wang, Wei W wrote:
> On Saturday, December 16, 2017 3:22 AM, Matthew Wilcox wrote:
> > On Fri, Dec 15, 2017 at 10:49:15AM -0800, Matthew Wilcox wrote:
> > > Here's the API I'm looking at right now. The user need take no lock;
> > > the locking (spinlock) is handled internally to the implementation.
>
> Another place I saw your comment " The xb_ API requires you to handle your
> own locking" which seems conflict with the above "the user need take no lock".
> Doesn't the caller need a lock to avoid concurrent accesses to the ida bitmap?
Yes, the xb_ implementation requires you to handle your own locking.
The xbit_ API that I'm proposing will take care of the locking for you.
There's also no preallocation in the API.
> We'll change it to "bool xb_find_set(.., unsigned long *result)", returning
> false indicates no "1" bit is found.
I put a replacement proposal in the next paragraph:
bool xbit_find_set(struct xbitmap *, unsigned long *start, unsigned long max);
Maybe 'start' is the wrong name for that parameter. Let's call it 'bit'.
It's both "where to start" and "first bit found".
> > - xbit_clear() can't return an error. Neither can xbit_zero().
>
> I found the current xbit_clear implementation only returns 0, and there isn't
> an error to be returned from this function. In this case, is it better to
> make the function "void"?
Yes, I think so.
My only qualm is that I've been considering optimising the memory
consumption when an entire 1024-bit chunk is full; instead of keeping a
pointer to a 128-byte entry full of ones, store a special value in the
radix tree which means "every bit is set".
The downside is that we then have to pass GFP flags to xbit_clear() and
xbit_zero(), and they can fail. It's not clear to me whether that's a
good tradeoff.
> Are you suggesting to rename the current xb_ APIs to the above xbit_ names
> (with parameter changes)?
>
> Why would we need xbit_alloc, which looks like ida_get_new, I think set/clear
> should be adequate to the current usages.
I'm intending on replacing the xb_ and ida_ implementations with this one.
It removes the preload API which makes it easier to use, and it handles
the locking for you.
But I need to get the XArray (which replaces the radix tree) finished first.
- Re: [Qemu-devel] [PATCH v19 3/7] xbitmap: add more operations, (continued)
- Re: [Qemu-devel] [PATCH v19 3/7] xbitmap: add more operations, Tetsuo Handa, 2017/12/14
- Re: [Qemu-devel] [PATCH v19 3/7] xbitmap: add more operations, Matthew Wilcox, 2017/12/14
- Re: [Qemu-devel] [PATCH v19 3/7] xbitmap: add more operations, Tetsuo Handa, 2017/12/15
- Re: [Qemu-devel] [PATCH v19 3/7] xbitmap: add more operations, Michael S. Tsirkin, 2017/12/15
- Re: [Qemu-devel] [PATCH v19 3/7] xbitmap: add more operations, Tetsuo Handa, 2017/12/15
- Re: [Qemu-devel] [PATCH v19 3/7] xbitmap: add more operations, Matthew Wilcox, 2017/12/16
- Re: [Qemu-devel] [PATCH v19 3/7] xbitmap: add more operations, Tetsuo Handa, 2017/12/16
- Re: [Qemu-devel] [PATCH v19 3/7] xbitmap: add more operations, Matthew Wilcox, 2017/12/15
- Re: [Qemu-devel] [PATCH v19 3/7] xbitmap: add more operations, Matthew Wilcox, 2017/12/15
- Re: [Qemu-devel] [PATCH v19 3/7] xbitmap: add more operations, Wang, Wei W, 2017/12/17
- Re: [Qemu-devel] [PATCH v19 3/7] xbitmap: add more operations,
Matthew Wilcox <=
- Re: [Qemu-devel] [PATCH v19 3/7] xbitmap: add more operations, Wei Wang, 2017/12/17
- Re: [Qemu-devel] [PATCH v19 3/7] xbitmap: add more operations, Matthew Wilcox, 2017/12/17
- Re: [Qemu-devel] [PATCH v19 3/7] xbitmap: add more operations, Wei Wang, 2017/12/16
- Re: [Qemu-devel] [PATCH v19 3/7] xbitmap: add more operations, Matthew Wilcox, 2017/12/14
Re: [Qemu-devel] [PATCH v19 3/7] xbitmap: add more operations, Matthew Wilcox, 2017/12/15
- Re: [Qemu-devel] [PATCH v19 3/7] xbitmap: add more operations, Wei Wang, 2017/12/16
- Re: [Qemu-devel] [PATCH v19 3/7] xbitmap: add more operations, Tetsuo Handa, 2017/12/16
- Re: [Qemu-devel] [PATCH v19 3/7] xbitmap: add more operations, Wei Wang, 2017/12/17
- Re: [Qemu-devel] [PATCH v19 3/7] xbitmap: add more operations, Tetsuo Handa, 2017/12/17
- Re: [Qemu-devel] [PATCH v19 3/7] xbitmap: add more operations, Wang, Wei W, 2017/12/17