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	id 794CB68B05; Wed, 24 Jun 2026 17:42:41 +0200 (CEST)
Date: Wed, 24 Jun 2026 17:42:41 +0200
From: Christoph Hellwig <hch@lst.de>
To: Carlos Maiolino <cem@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>, Jan Kara <jack@suse.cz>,
	Filip Blagojevic <filip.blagojevic@wdc.com>,
	Matthew Wilcox <willy@infradead.org>,
	Damien Le Moal <dlemoal@kernel.org>, linux-fsdevel@vger.kernel.org,
	linux-xfs@vger.kernel.org
Subject: Re: update BDI {io,ra}_pages values based on the RT device limits
Message-ID: <20260624154241.GB13186@lst.de>
References: <20260623142109.1838702-1-hch@lst.de> <ajuxIMzTbzxEuX5g@nidhogg.toxiclabs.cc>
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On Wed, Jun 24, 2026 at 12:40:50PM +0200, Carlos Maiolino wrote:
> Giving the current tendency of filesystems being multi-device, this
> doesn't sound bad IMHO. Wouldn't accessing io_pages of each BDI also be
> worth even for a journal dev? I wonder if what you ran into wouldn't be
> possible if somebody would be using just a SSD for journal and a non-rt
> XFS on a HDD or a different/slower device.

Nothing looks at the value for the log device.

> 
> I don't know how stupid that sounds but perhaps it wouldn't be that
> complicated to support multiple BDIs without making it unpleasant for
> filesystems that don't care?
> sb->bdi could be turned into a dynamic array and a new sb->s_devcount
> fields to keep track of it on multi-device filesystems. Filesystems who
> don't care about multiple BDIs would have it pointing to a single BDI
> struct. Again I feel I'm missing something, so it might sound really
> stupid :)

This will get complicated really soon..