Re: [dpdk-stable] [PATCH 3/5] mbuf: fix free_space setting for dynamic field

[Olivier Matz <olivier.matz@6wind.com>]

On Sat, Jun 13, 2020 at 11:49:19PM +0800, Xiaolong Ye wrote:
> The value free_space[i] is used to save the size of biggest aligned
> element that can fit in the zone, current implementation has one flaw,
> for example, if user registers dynfield1 (size = 4, align = 4, req = 124)
> first, the free_space would be as below after registration:
> 
>   0070: 08 08 08 08 08 08 08 08
>   0078: 08 08 08 08 00 00 00 00
> 
> Then if user continues to register dynfield2 (size = 4, align = 4),
> free_space would become:
> 
>   0070: 00 00 00 00 04 04 04 04
>   0078: 04 04 04 04 00 00 00 00
> 
> Further request dynfield3 (size = 8, align = 8) would fail to register
> due to alignment requirement can't be satisfied, though there is enough
> space remained in mbuf.
> 
> This patch fixes above issue by saving alignment only in aligned zone,
> after the fix, above registrations order can be satisfied, free_space
> would be like:
> 
> After dynfield1 registration:
> 
>   0070: 08 08 08 08 08 08 08 08
>   0078: 04 04 04 04 00 00 00 00
> 
> After dynfield2 registration:
> 
>   0070: 08 08 08 08 08 08 08 08
>   0078: 00 00 00 00 00 00 00 00
> 
> After dynfield3 registration:
> 
>   0070: 00 00 00 00 00 00 00 00
>   0078: 00 00 00 00 00 00 00 00
> 
> This patch also reduces iterations in process_score() by jumping align
> steps in each loop.
> 
> Fixes: 4958ca3a443a ("mbuf: support dynamic fields and flags")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Xiaolong Ye <xiaolong.ye@intel.com>

Acked-by: Olivier Matz <olivier.matz@6wind.com>

Thanks!