linux-kernel - Re: [PATCH] pmem: export the symbols __copy_user_flushcache and __copy_from_user

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Message-ID: <alpine.LRH.2.02.2009161254400.745@file01.intranet.prod.int.rdu2.redhat.com>
Date:   Wed, 16 Sep 2020 13:24:12 -0400 (EDT)
From:   Mikulas Patocka <mpatocka@...hat.com>
To:     Dan Williams <dan.j.williams@...el.com>
cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Matthew Wilcox <willy@...radead.org>, Jan Kara <jack@...e.cz>,
        Eric Sandeen <esandeen@...hat.com>,
        Dave Chinner <dchinner@...hat.com>,
        "Kani, Toshi" <toshi.kani@....com>,
        "Norton, Scott J" <scott.norton@....com>,
        "Tadakamadla, Rajesh (DCIG/CDI/HPS Perf)" 
        <rajesh.tadakamadla@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>
Subject: Re: [PATCH] pmem: export the symbols __copy_user_flushcache and
 __copy_from_user_flushcache



On Wed, 16 Sep 2020, Dan Williams wrote:

> On Wed, Sep 16, 2020 at 3:57 AM Mikulas Patocka <mpatocka@...hat.com> wrote:
> >
> >
> >
> > I'm submitting this patch that adds the required exports (so that we could
> > use __copy_from_user_flushcache on x86, arm64 and powerpc). Please, queue
> > it for the next merge window.
> 
> Why? This should go with the first user, and it's not clear that it
> needs to be relative to the current dax_operations export scheme.

Before nvfs gets included in the kernel, I need to distribute it as a 
module. So, it would make my maintenance easier. But if you don't want to 
export it now, no problem, I can just copy __copy_user_flushcache from the 
kernel to the module.

> My first question about nvfs is how it compares to a daxfs with
> executables and other binaries configured to use page cache with the
> new per-file dax facility?

nvfs is faster than dax-based filesystems on metadata-heavy operations 
because it doesn't have the overhead of the buffer cache and bios. See 
this: http://people.redhat.com/~mpatocka/nvfs/BENCHMARKS

Mikulas