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Date:   Tue, 30 May 2023 07:45:47 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     David Sterba <dsterba@suse.cz>
Cc:     Christoph Hellwig <hch@lst.de>, Chris Mason <clm@fb.com>,
        Josef Bacik <josef@toxicpanda.com>,
        David Sterba <dsterba@suse.com>, linux-btrfs@vger.kernel.org,
        Matthew Wilcox <willy@infradead.org>, linux-mm@kvack.org
Subject: Re: [PATCH 08/16] btrfs: stop setting PageError in the data I/O
 path
Message-ID: <20230530054547.GA5825@lst.de>
References: <20230523081322.331337-1-hch@lst.de> <20230523081322.331337-9-hch@lst.de> <20230529175210.GL575@twin.jikos.cz>
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On Mon, May 29, 2023 at 07:52:10PM +0200, David Sterba wrote:
> On Tue, May 23, 2023 at 10:13:14AM +0200, Christoph Hellwig wrote:
> > PageError is not used by the VFS/MM and deprecated.
> 
> Is there some reference other than code? I remember LSF/MM talks about
> writeback, reducing page flags but I can't find anything that would say
> that PageError is not used anymore. For such core changes in the
> neighboring subysystems I kind of rely on lwn.net, hearsay or accidental
> notice on fsdevel.
> 
> Removing the Error bit handling looks overall good but I'd also need to
> refresh my understanding of the interactions with writeback.

willy is the driving force behind the PageErro removal, so maybe he
has a coherent writeup.  But the basic idea is:

 - page flag space availability is limited, and killing any one we can
   easily is a good thing
 - PageError is not well defined and not part of any VM or VFS contract,
   so in addition to freeing up space it also generally tends to remove
   confusion.