linux-kernel - Re: [PATCH v3 1/1] nvmet-tcp: Don't kmap() pages which can't come from HIGHMEM

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Message-ID: <YwkgdYNkjNWkz+Gv@ZenIV>
Date:   Fri, 26 Aug 2022 20:35:17 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Keith Busch <kbusch@...nel.org>
Cc:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        Chaitanya Kulkarni <kch@...dia.com>,
        James Smart <james.smart@...adcom.com>,
        Ira Weiny <ira.weiny@...el.com>,
        "Venkataramanan, Anirudh" <anirudh.venkataramanan@...el.com>,
        linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Chaitanya Kulkarni <chaitanyak@...dia.com>
Subject: Re: [PATCH v3 1/1] nvmet-tcp: Don't kmap() pages which can't come
 from HIGHMEM

On Fri, Aug 26, 2022 at 12:35:09PM -0600, Keith Busch wrote:

> > Can you please provide further information or links to documentation?
> 
> This kvec/bvec talk is a digression from your original goal: reduce unnecessary
> kmap() usage. If anyone wants to take on the bvec optimization in this code
> path, then by all means lets do it in a separate patch.

Oh?  And why is a switch to iov_iter_bvec() *not* a reduction of kmap() usage?
ITER_BVEC methods use kmap_local() for data transfers, TYVM...