linux-kernel - Re: [PATCH 0/2] mm: Fix NFS swapfiles and use DIO read for swapfiles

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Message-ID: <20210812121834.GA18532@lst.de>
Date:   Thu, 12 Aug 2021 14:18:34 +0200
From:   Christoph Hellwig <hch@....de>
To:     David Howells <dhowells@...hat.com>
Cc:     willy@...radead.org, trond.myklebust@...marydata.com,
        darrick.wong@...cle.com, hch@....de, jlayton@...nel.org,
        sfrench@...ba.org, torvalds@...ux-foundation.org,
        linux-nfs@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] mm: Fix NFS swapfiles and use DIO read for
 swapfiles

On Thu, Aug 12, 2021 at 12:57:41PM +0100, David Howells wrote:
> 
> Hi Willy, Trond,
> 
> Here's a change to make reads from the swapfile use async DIO rather than
> readpage(), as requested by Willy.
> 
> Whilst trying to make this work, I found that NFS's support for swapfiles
> seems to have been non-functional since Aug 2019 (I think), so the first
> patch fixes that.  Question is: do we actually *want* to keep this
> functionality, given that it seems that no one's tested it with an upstream
> kernel in the last couple of years?

Independ of the NFS use using the direct I/O code for swap seems like
the right thing to do in generlal.  e.g. for XFS a lookup in the extent
btree will be more efficient than the weird swap extent map.