linux-kernel - Re: [PATCH 01/17] mm/highmem: Lift memcpy_[to|from]_page and memset

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Message-ID: <20201124202040.GF4327@casper.infradead.org>
Date:   Tue, 24 Nov 2020 20:20:40 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Ira Weiny <ira.weiny@...el.com>
Cc:     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>,
        Thomas Gleixner <tglx@...utronix.de>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Patrik Jakobsson <patrik.r.jakobsson@...il.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        David Howells <dhowells@...hat.com>, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>,
        Steve French <sfrench@...ba.org>,
        Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <yuchao0@...wei.com>,
        Nicolas Pitre <nico@...xnic.net>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Brian King <brking@...ibm.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jérôme Glisse <jglisse@...hat.com>,
        Kirti Wankhede <kwankhede@...dia.com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 01/17] mm/highmem: Lift memcpy_[to|from]_page and
 memset_page to core

On Tue, Nov 24, 2020 at 11:21:13AM -0800, Ira Weiny wrote:
> On Tue, Nov 24, 2020 at 02:19:41PM +0000, Matthew Wilcox wrote:
> > On Mon, Nov 23, 2020 at 10:07:39PM -0800, ira.weiny@...el.com wrote:
> > > +static inline void memzero_page(struct page *page, size_t offset, size_t len)
> > > +{
> > > +	memset_page(page, 0, offset, len);
> > > +}
> > 
> > This is a less-capable zero_user_segments().
> 
> Actually it is a duplicate of zero_user()...  Sorry I did not notice those...
> :-(
> 
> Why are they called '_user_'?

git knows ...

commit 01f2705daf5a36208e69d7cf95db9c330f843af6
Author: Nate Diller <nate.diller@...il.com>
Date:   Wed May 9 02:35:07 2007 -0700

    fs: convert core functions to zero_user_page
    
    It's very common for file systems to need to zero part or all of a page,
    the simplist way is just to use kmap_atomic() and memset().  There's
    actually a library function in include/linux/highmem.h that does exactly
    that, but it's confusingly named memclear_highpage_flush(), which is
    descriptive of *how* it does the work rather than what the *purpose* is.
    So this patchset renames the function to zero_user_page(), and calls it
    from the various places that currently open code it.
    
    This first patch introduces the new function call, and converts all the
    core kernel callsites, both the open-coded ones and the old
    memclear_highpage_flush() ones.  Following this patch is a series of
    conversions for each file system individually, per AKPM, and finally a
    patch deprecating the old call.  The diffstat below shows the entire
    patchset.