netdev - Re: [PATCH net-next-mlx5 02/13] net/mlx5: Add new driver lib for mappings unique ids to data

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Message-ID: <85bf4ee7-e006-18ea-d643-8b9001066cbf@mellanox.com>
Date:   Wed, 22 Jan 2020 12:17:44 +0000
From:   Paul Blakey <paulb@...lanox.com>
To:     Leon Romanovsky <leon@...nel.org>
CC:     Saeed Mahameed <saeedm@...lanox.com>,
        Oz Shlomo <ozsh@...lanox.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Vlad Buslov <vladbu@...lanox.com>,
        David Miller <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Jiri Pirko <jiri@...nulli.us>
Subject: Re: [PATCH net-next-mlx5 02/13] net/mlx5: Add new driver lib for
 mappings unique ids to data


On 1/21/2020 9:04 PM, Leon Romanovsky wrote:
> On Tue, Jan 21, 2020 at 06:16:11PM +0200, Paul Blakey wrote:
>> Add a new interface for mapping data to a given id range (max_id),
>> and back again. It supports variable sized data, and different
>> allocators, and read/write locks.
>>
>> This mapping interface also supports delaying the mapping removal via
>> a workqueue. This is for cases where we need the mapping to have
>> some grace period in regards to finding it back again, for example
>> for packets arriving from hardware that were marked with by a rule
>> with an old mapping that no longer exists.
>>
>> We also provide a first implementation of the interface is idr_mapping
>> that uses idr for the allocator and a mutex lock for writes
>> (add/del, but not for find).
>>
>> Signed-off-by: Paul Blakey <paulb@...lanox.com>
>> Reviewed-by: Oz Shlomo <ozsh@...lanox.com>
>> Reviewed-by: Mark Bloch <markb@...lanox.com>
>> ---
> I have many issues with this patch, but two main are:
> 1. This is general implementation without proper documentation and test
> which doesn't belong to driver code.
> 2. It looks very similar to already existing code, for example xarray.
>
> Thanks
This data structure uses idr (currently wrapper for xarray) but also a 
hash table, refcount, and
generic allocators.
The hashtable is used on top of the idr to find if data added to the 
mapping already exists, if it
does it updates a refcount.
We also have some special delayed removal for our use case.
The addition to xarray is translation from data to hash function. It is 
something that doesn't exist
and needs extra code. IDR was chosen as being simplified interface of 
xarray and it is good enough
in our case.

The mlx5 is first user of such library, once the other user will arrive, 
we will be happy to
collaborate in order to make it generic.