linux-kernel - Re: [RFC] synchronous readpage for buffer

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Message-ID: <20201023114220.GY20115@casper.infradead.org>
Date:   Fri, 23 Oct 2020 12:42:20 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Hannes Reinecke <hare@...e.de>
Cc:     linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC] synchronous readpage for buffer_heads

On Fri, Oct 23, 2020 at 08:22:07AM +0200, Hannes Reinecke wrote:
> On 10/22/20 5:22 PM, Matthew Wilcox wrote:
> Hmm. You are aware, of course, that hch et al are working on replacing bhs
> with iomap, right?

$ git shortlog --author=Wilcox origin/master -- fs/iomap |head -1
Matthew Wilcox (Oracle) (17):

But actually, I don't see anyone working on a mass migration of
filesystems from either using BHs directly or using the mpage code to
using iomap.  I have a summer student for next summer who I'm going to
let loose on this problem, but I fear buffer_heads will be with us for
a long time to come.

I mean, who's going to convert reiserfs to iomap?
$ git log --no-merges --since=2015-01-01 origin/master fs/reiserfs |grep -c ^comm
130

Not exactly a thriving development community.  It doesn't even support
fallocate.

> So wouldn't it be more useful to concentrate on the iomap code, and ensure
> that _that_ is working correctly?

Did that one first, then did mpage_readpage(), now I've moved on to
block_read_full_page().  Now I'm going to go back and redo iomap
with everything I learned doing block_read_full_page().  It's going
to use blk_completion.