linux-kernel - Re: kmap_local semantics

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Message-ID: <20210312153646.GE3014244@iweiny-DESK2.sc.intel.com>
Date:   Fri, 12 Mar 2021 07:36:46 -0800
From:   Ira Weiny <ira.weiny@...el.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org
Subject: Re: kmap_local semantics

On Fri, Mar 12, 2021 at 07:54:13AM +0100, Christoph Hellwig wrote:
> So with the new kmap_local interface is it possible / advisable to
> use local kmaps over code that might schedule(), e.g. to wait for I/O?

It is possible yes.  "Advisable" I think so.  Thomas knows better than I what
performance would be.

FWIW I have been working on converting kmaps to kmap_local.  Most of the
instances don't schedule AFAICT.

What I really don't want to see is any kmap'ings handed to another thread.  I
am working hard to eliminate the use of kmap for that use.  Is that going to be
a problem?

Ira