linux-kernel - Re: [PATCH V2 2/2] mm/highmem: Lift memcpy_[to|from]

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Message-ID: <20201208163814.GN1563847@iweiny-DESK2.sc.intel.com>
Date:   Tue, 8 Dec 2020 08:38:14 -0800
From:   Ira Weiny <ira.weiny@...el.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Eric Biggers <ebiggers@...nel.org>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH V2 2/2] mm/highmem: Lift memcpy_[to|from]_page to core

On Tue, Dec 08, 2020 at 12:23:16PM +0000, Matthew Wilcox wrote:
> On Mon, Dec 07, 2020 at 02:57:03PM -0800, ira.weiny@...el.com wrote:
> > Placing these functions in 'highmem.h' is suboptimal especially with the
> > changes being proposed in the functionality of kmap.  From a caller
> > perspective including/using 'highmem.h' implies that the functions
> > defined in that header are only required when highmem is in use which is
> > increasingly not the case with modern processors.  Some headers like
> > mm.h or string.h seem ok but don't really portray the functionality
> > well.  'pagemap.h', on the other hand, makes sense and is already
> > included in many of the places we want to convert.
> 
> pagemap.h is for the page cache.  It's not for "random page
> functionality".  Yes, I know it's badly named.  No, I don't want to
> rename it.  These helpers should go in highmem.h along with zero_user().

I could have sworn you suggested pagemap.h.  But I can't find the evidence on
lore.  :-/   hehehe...

In the end the code does not care.  I have a distaste for highmem.h because it
is no longer for 'high memory'.  And I think a number of driver writers who are
targeting 64bit platforms just don't care any more.  So as we head toward
memory not being mapped by the kernel for other reasons I think highmem needs
to be 'rebranded' if not renamed.

Ira