linux-kernel - Re: [PATCH rdma-next v1 1/4] lib/scatterlist: Refactor sg_alloc_table_from

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Message-ID: <20200915161643.GA24320@lst.de>
Date:   Tue, 15 Sep 2020 18:16:43 +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 v1 1/4] lib/scatterlist: Refactor
 sg_alloc_table_from_pages

On Thu, Sep 10, 2020 at 04:42:56PM +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.
> 
> Signed-off-by: Maor Gottlieb <maorg@...dia.com>
> Signed-off-by: Leon Romanovsky <leonro@...dia.com>

I really don't think this refactoring on its own adds any value,
it just makes reading the rest of the series harder.

(functionally it looks correct, though)