linux-kernel - Re: [RFC PATCH v2 5/5] mm: Remove swap BIO paths and only use DIO paths [BROKEN]

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Date:   Fri, 13 Aug 2021 09:14:15 +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, viro@...iv.linux.org.uk,
        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: [RFC PATCH v2 5/5] mm: Remove swap BIO paths and only use DIO
 paths [BROKEN]

On Thu, Aug 12, 2021 at 09:22:41PM +0100, David Howells wrote:
> [!] NOTE: This doesn't work and might damage your disk's contents.
> 
> Delete the BIO-generating swap read/write paths and always use
> ->direct_IO().  This puts the mapping layer in the filesystem.
> 
> This doesn't work - probably due to ki_pos being set to
> page_file_offset(page) which then gets remapped.

Also because most common block file systems do not actually implement
a ->direct_IO that does anything (noop_direct_IO).