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Date:   Thu, 15 Jun 2023 13:16:11 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Christoph Hellwig <hch@lst.de>
Cc:     Hannes Reinecke <hare@suse.de>, linux-fsdevel@vger.kernel.org,
        linux-block@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Luis Chamberlain <mcgrof@kernel.org>
Subject: Re: [PATCH 1/2] highmem: Add memcpy_to_folio()
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On Thu, Jun 15, 2023 at 07:58:31AM +0200, Christoph Hellwig wrote:
> On Wed, Jun 14, 2023 at 02:48:52PM +0100, Matthew Wilcox (Oracle) wrote:
> > This is the folio equivalent of memcpy_to_page(), but it handles large
> > highmem folios.  It may be a little too big to inline on systems that
> > have CONFIG_HIGHMEM enabled but on systems we actually care about almost
> > all the code will be eliminated.
> 
> I suspect the right thing is to have the trivial version without kmapping
> for !HIGHMEM inline, and a separate version with the kmap loop out of
> line for HIGHMEM builds.
> 
> Same for the next patch.

Yeah, that's what I did to zero_user_segments().  As time goes by,
I'm starting to care about performance of CONFIG_HIGHMEM systems less
and less.