linux-kernel - Re: [PATCH] mm: always respect QUEUE_FLAG_STABLE

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Date:   Thu, 4 May 2023 17:16:48 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Jan Kara <jack@...e.cz>
Cc:     Christoph Hellwig <hch@....de>, Ilya Dryomov <idryomov@...il.com>,
        Johannes Thumshirn <johannes.thumshirn@....com>,
        Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: always respect QUEUE_FLAG_STABLE_WRITES on the block
 device

On Thu, May 04, 2023 at 05:55:56PM +0200, Jan Kara wrote:
> For bdev address_space that's easy but what Ilya also mentioned is a
> problem when 'stable_write' flag gets toggled on the device and in that
> case having to propagate the flag update to all the address_space
> structures is a nightmare...

We have a number of flags which don't take effect when modified on a
block device with a mounted filesystem on it.  For example, modifying
the readahead settings do not change existing files, only new ones.
Since this flag is only modifiable for debugging purposes, I think I'm
OK with it not affecting already-mounted filesystems.  It feels like a
decision that reasonable people could disagree on, though.