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

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Date:   Wed, 16 Sep 2020 14:06:31 -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 10:24 AM Mikulas Patocka <mpatocka@...hat.com> wrote:
> >
> > > 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
> 
> ...and that metadata problem is intractable upstream? Christoph poked
> at bypassing the block layer for xfs metadata operations [1], I just
> have not had time to carry that further.
> 
> [1]: "xfs: use dax_direct_access for log writes", although it seems
> he's dropped that branch from his xfs.git

XFS is very big. I wanted to create something small.

Mikulas