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Date:   Thu, 22 Jul 2021 05:14:20 +0100
From:   Christoph Hellwig <hch@infradead.org>
To:     Matthew Wilcox <willy@infradead.org>
Cc:     Shyam Prasad N <nspmangalore@gmail.com>,
        David Howells <dhowells@redhat.com>,
        Steve French <smfrench@gmail.com>,
        CIFS <linux-cifs@vger.kernel.org>
Subject: Re: Classification of reads within a filesystem
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On Wed, Jul 21, 2021 at 06:52:05PM +0100, Matthew Wilcox wrote:
> Oh ... except for swap.  For NFS only, it calls ->readpage, so it really
> wants ->readpage to be async so it can kick off multiple pages and
> then wait for the one it actually needs.  That gets into a conversation
> about how much we really care about swap-over-NFS, whether swap should
> be using ->readpage or ->direct_IO, and whether swap should use the
> file readahead code or its own virtual address based readahead code.
> Most of those discussions are outside my area of expertise.

It really should be using direct I/O.  I think one issue back in the
day was the odd locking requirements for swap, but that's something we
could overcome.