linux-kernel - [PATCH/RFC] nfs: NFS_SWAP should depend on SWAP

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Date:   Mon, 30 Dec 2019 16:32:38 +0100
From:   Geert Uytterhoeven <geert+renesas@...der.be>
To:     Trond Myklebust <trond.myklebust@...merspace.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-nfs@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Geert Uytterhoeven <geert+renesas@...der.be>
Subject: [PATCH/RFC] nfs: NFS_SWAP should depend on SWAP

If CONFIG_SWAP=n, it does not make much sense to offer the user the
option to enable support for swapping over NFS, as that will still fail
at run time:

    # swapon /swap
    swapon: /swap: swapon failed: Function not implemented

Fix this by adding a dependency on CONFIG_SWAP.

Fixes: a564b8f0398636ba ("nfs: enable swap on NFS")
Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
---
Marked RFC, as this still doesn't seem to work.
When enabled, the kernel log is spammed with:

    [  449.371536] __swap_writepage: 413288 callbacks suppressed
    [  449.371577] Write error on dio swapfile (10047488)
    [  449.382435] Write error on dio swapfile (14147584)
    [  449.387320] Write error on dio swapfile (10919936)
    [  449.392474] Write error on dio swapfile (8945664)
    [  449.397263] Write error on dio swapfile (24256512)
    [  449.402330] Write error on dio swapfile (14307328)
    [  449.407195] Write error on dio swapfile (229376)
    [  449.412031] Write error on dio swapfile (10293248)
    [  449.416891] Write error on dio swapfile (2007040)

Platform is 32-bit Cortex A9 with 32 MiB of RAM (hence the need for
swap).
---
 fs/nfs/Kconfig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/nfs/Kconfig b/fs/nfs/Kconfig
index 295a7a21b7744014..e7dd07f47825939e 100644
--- a/fs/nfs/Kconfig
+++ b/fs/nfs/Kconfig
@@ -90,7 +90,7 @@ config NFS_V4
 config NFS_SWAP
 	bool "Provide swap over NFS support"
 	default n
-	depends on NFS_FS
+	depends on NFS_FS && SWAP
 	select SUNRPC_SWAP
 	help
 	  This option enables swapon to work on files located on NFS mounts.
-- 
2.17.1