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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Mon, 7 Feb 2022 18:55:48 +0100
Message-ID: <CAMuHMdXw6bhOf8BMWzje1h_gaBg8TxZXWAQgL0cpdYBkZ+LwXw@mail.gmail.com>
Subject: Re: [PATCH 00/23 V3] Repair SWAP-over_NFS
To:     NeilBrown <neilb@suse.de>
Cc:     Trond Myklebust <trond.myklebust@hammerspace.com>,
        Anna Schumaker <anna.schumaker@netapp.com>,
        Chuck Lever <chuck.lever@oracle.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mel Gorman <mgorman@suse.de>,
        Christoph Hellwig <hch@infradead.org>,
        David Howells <dhowells@redhat.com>,
        "open list:NFS, SUNRPC, AND..." <linux-nfs@vger.kernel.org>,
        Linux MM <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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Hi Neil,

On Mon, Jan 24, 2022 at 5:40 PM NeilBrown <neilb@suse.de> wrote:
> swap-over-NFS currently has a variety of problems.
>
> swap writes call generic_write_checks(), which always fails on a swap
> file, so it completely fails.
> Even without this, various deadlocks are possible - largely due to
> improvements in NFS memory allocation (using NOFS instead of ATOMIC)
> which weren't tested against swap-out.
>
> NFS is the only filesystem that has supported fs-based swap IO, and it
> hasn't worked for several releases, so now is a convenient time to clean
> up the swap-via-filesystem interfaces - we cannot break anything !
>
> So the first few patches here clean up and improve various parts of the
> swap-via-filesystem code.  ->activate_swap() is given a cleaner
> interface, a new ->swap_rw is introduced instead of burdening
> ->direct_IO, etc.
>
> Current swap-to-filesystem code only ever submits single-page reads and
> writes.  These patches change that to allow multi-page IO when adjacent
> requests are submitted.  Writes are also changed to be async rather than
> sync.  This substantially speeds up write throughput for swap-over-NFS.
>
> Some of the NFS patches can land independently of the MM patches.  A few
> require the MM patches to land first.

Thanks for your series!
Swap over NFS was indeed broken last time I tried[1], but with your
series, it's working again on arm32 (RZ/A1 with 32 MiB of RAM, 100Mbps
Ethernet and Debian 9 nfsroot). My system was exercised using "apt
update", and the subsequent "apt upgrade" is still running, though
(it took more than 6 hours to build the apt dependency tree, now it's
trying hard to create a list of packages...).

Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>

BTW, I think you do want to run scripts/checkpatch.pl on your series,
and improve it by fixing a few of the reported warnings (function
definition arguments should also have an identifier name, missing
data_race() comment, missing SPDX-License-Identifier tag).

[1] https://lore.kernel.org/all/20191230153238.29878-1-geert+renesas@glider.be/

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds