linux-kernel - Re: NVFS XFS metadata (was: [PATCH] pmem: export the symbols __copy_user_flushcache and __copy_from_user

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Date:   Wed, 23 Sep 2020 16:04:27 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Mikulas Patocka <mpatocka@...hat.com>
Cc:     Jan Kara <jack@...e.cz>, Dave Chinner <david@...morbit.com>,
        Dan Williams <dan.j.williams@...el.com>,
        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>,
        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: NVFS XFS metadata (was: [PATCH] pmem: export the symbols
 __copy_user_flushcache and __copy_from_user_flushcache)

On Wed, Sep 23, 2020 at 09:11:43AM -0400, Mikulas Patocka wrote:
> I also don't know how to implement journling on persistent memory :) On 
> EXT4 or XFS you can pin dirty buffers in memory until the journal is 
> flushed. This is obviously impossible on persistent memory. So, I'm 
> considering implementing only some lightweight journaling that will 
> guarantee atomicity between just a few writes.

That's a bit disappointing considering people have been publishing
papers on how to do umpteen different variations on persistent memory
journalling for the last five years.

https://www.google.com/search?q=intel+persistent+memory+atomic+updates

for example