Re: [PATCH rdma-next 1/4] lib/scatterlist: Refactor sg_alloc_table_from_pages

From: Christoph Hellwig
Date: Tue Sep 08 2020 - 15:42:41 EST

On Mon, Sep 07, 2020 at 03:32:31PM +0300, Maor Gottlieb wrote:
> 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@xxxxxxxxxx>
>>> 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.

Feel free to keep it for now, we can sort this out later.