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

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Message-ID: <20200907072912.GA19875@lst.de>
Date:   Mon, 7 Sep 2020 09:29:12 +0200
From:   Christoph Hellwig <hch@....de>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     Christoph Hellwig <hch@....de>, Doug Ledford <dledford@...hat.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Maor Gottlieb <maorg@...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 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?