linux-kernel - Re: [RFC PATCH] nvmet-tcp: Don't kmap() pages which can't come from HIGHMEM

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Date:   Tue, 16 Aug 2022 12:59:49 -0600
From:   Keith Busch <kbusch@...nel.org>
To:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>
Cc:     Christoph Hellwig <hch@....de>, Sagi Grimberg <sagi@...mberg.me>,
        Chaitanya Kulkarni <kch@...dia.com>,
        linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Ira Weiny <ira.weiny@...el.com>
Subject: Re: [RFC PATCH] nvmet-tcp: Don't kmap() pages which can't come from
 HIGHMEM

On Tue, Aug 16, 2022 at 11:18:08AM +0200, Fabio M. De Francesco wrote:
> 
> Therefore, I have two questions: am I right about thinking that the pages
> mapped in nvmet_tcp_map_pdu_iovec() are allocated with GFP_KERNEL? 

I think you are correct.

> If so, can anyone with more knowledge than mine please say if my changes make
> any sense?

I think it does make sense. I like the code simplification, though this use
was't really paying the kmap penalty since, as you mentioned, this is never
highmem.

You should also remove the cmd's 'nr_mapped' field while you're at it,
otherwise you'll hit the WARN in nvmet_tcp_free_cmd_buffers().