linux-kernel - Re: [PATCH 01/18] mm: add a kunmap_local

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Date:   Fri, 18 Jun 2021 11:37:28 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Ira Weiny <ira.weiny@...el.com>
Cc:     Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...nel.dk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Geoff Levand <geoff@...radead.org>,
        Ilya Dryomov <idryomov@...il.com>,
        Dongsheng Yang <dongsheng.yang@...ystack.cn>,
        Mike Snitzer <snitzer@...hat.com>,
        "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
        dm-devel@...hat.com, linux-mips@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, ceph-devel@...r.kernel.org,
        linux-arch@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Christoph Lameter <cl@...two.de>
Subject: Re: [PATCH 01/18] mm: add a kunmap_local_dirty helper

On Thu, Jun 17, 2021 at 08:01:57PM -0700, Ira Weiny wrote:
>
> > +		flush_kernel_dcache_page(__page);		\
> 
> Is this required on 32bit systems?  Why is kunmap_flush_on_unmap() not
> sufficient on 64bit systems?  The normal kunmap_local() path does that.
> 
> I'm sorry but I did not see a conclusion to my query on V1. Herbert implied the
> he just copied from the crypto code.[1]  I'm concerned that this _dirty() call
> is just going to confuse the users of kmap even more.  So why can't we get to
> the bottom of why flush_kernel_dcache_page() needs so much logic around it
> before complicating the general kernel users.
> 
> I would like to see it go away if possible.

This thread may be related:

https://lwn.net/Articles/240249/

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt