linux-kernel - Re: [PATCH rdma-next 1/4] lib/scatterlist: Refactor sg_alloc_table_from

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Date:   Mon, 7 Sep 2020 15:32:31 +0300
From:   Maor Gottlieb <maorg@...dia.com>
To:     Christoph Hellwig <hch@....de>, Leon Romanovsky <leon@...nel.org>
CC:     Doug Ledford <dledford@...hat.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        <linux-kernel@...r.kernel.org>, <linux-rdma@...r.kernel.org>
Subject: Re: [PATCH rdma-next 1/4] lib/scatterlist: Refactor
 sg_alloc_table_from_pages


On 9/7/2020 10:29 AM, Christoph Hellwig wrote:
> On Thu, Sep 03, 2020 at 06:54:34PM +0300, Leon Romanovsky wrote:
>> From: Maor Gottlieb <maorg@...dia.com>
>>
>> Currently, sg_alloc_table_from_pages doesn't support dynamic chaining of
>> SG entries. Therefore it requires from user to allocate all the pages in
>> advance and hold them in a large buffer. Such a buffer consumes a lot of
>> temporary memory in HPC systems which do a very large memory registration.
>>
>> The next patches introduce API for dynamically allocation from pages and
>> it requires us to do the following:
>>   * Extract the code to alloc_from_pages_common.
>>   * Change the build of the table to iterate on the chunks and not on the
>>     SGEs. It will allow dynamic allocation of more SGEs.
>>
>> Since sg_alloc_table_from_pages allocate exactly the number of chunks,
>> therefore chunks are equal to the number of SG entries.
> Given how few users __sg_alloc_table_from_pages has, what about just
> switching it to your desired calling conventions without another helper?

I tried it now. It didn't save a lot.  Please give me your decision and 
if needed I will update accordingly.