git: 89d5cbb82294 - main - libnv: optimize nvlist size calculation

[Kristof Provost]

On 11 Jun 2021, at 17:51, Mariusz Zaborski wrote:
> The branch main has been updated by oshogbo:
>
> URL: 
> https://cgit.FreeBSD.org/src/commit/?id=89d5cbb82294c8624e66f920d50353057ccab14b
>
> commit 89d5cbb82294c8624e66f920d50353057ccab14b
> Author:     Mariusz Zaborski <oshogbo at FreeBSD.org>
> AuthorDate: 2021-06-11 15:35:36 +0000
> Commit:     Mariusz Zaborski <oshogbo at FreeBSD.org>
> CommitDate: 2021-06-11 15:51:29 +0000
>
>     libnv: optimize nvlist size calculation
>
>     If we had a multiple nvlist, during nvlist_pack, we calculated the 
> size
>     of every nvlist separately. For example, if we had a nvlist with 
> three
>     nodes each containing another (A contains B, and B contains C), we 
> first
>     calculated the size of nvlist A (which contains B, C), then we 
> calculate
>     the size of B (which contains C, notice that we already did the
>     calculation of B, when we calculate A), and finally C. This means 
> that
>     this calculation was O(N!). This was done because each time we 
> pack
>     nvlist, we have to put its size in the header
>     (the separate header for A, B, and C).
>
>     To not break the ABI and to reduce the complexity of nvlist_size,
>     instead of calculating the nvlist size when requested,
>     we track the size of each nvlist.
>
>     Reported by:    pjd, kp
>     Tested by:      kp

Thanks for this!

Do you object to this being MFCd in a few days?

Thanks,
Kristof