linux-ext4 - Re: [PATCH v2 7/8] mm/migrate: enable noref migration for jbd2

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Message-ID: <rnhdk7ytdiiodckgc344novyknixn6jqeoy6bk4jjhtijjnc7z@qwofsm5ponwn>
Date: Thu, 10 Apr 2025 15:40:41 +0200
From: Jan Kara <jack@...e.cz>
To: Luis Chamberlain <mcgrof@...nel.org>
Cc: brauner@...nel.org, jack@...e.cz, tytso@....edu, 
	adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org, riel@...riel.com, dave@...olabs.net, 
	willy@...radead.org, hannes@...xchg.org, oliver.sang@...el.com, david@...hat.com, 
	axboe@...nel.dk, hare@...e.de, david@...morbit.com, djwong@...nel.org, 
	ritesh.list@...il.com, linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org, 
	linux-mm@...ck.org, gost.dev@...sung.com, p.raghav@...sung.com, da.gomez@...sung.com
Subject: Re: [PATCH v2 7/8] mm/migrate: enable noref migration for jbd2

On Wed 09-04-25 18:49:44, Luis Chamberlain wrote:
> From: Davidlohr Bueso <dave@...olabs.net>
> 
> Add semantics to enable future optimizations for buffer head noref jbd2
> migration. This adds a new BH_Migrate flag which ensures we can bail
> on the lookup path. This should enable jbd2 to get semantics of when
> a buffer head is under folio migration, and should yield to it and to
> eventually remove the buffer_meta() check skipping current jbd2 folio
> migration.
> 
> Suggested-by: Jan Kara <jack@...e.cz>
> Co-developed-by: Luis Chamberlain <mcgrof@...nel.org>
> Signed-off-by: Davidlohr Bueso <dave@...olabs.net>
> Signed-off-by: Luis Chamberlain <mcgrof@...nel.org>

..

> diff --git a/mm/migrate.c b/mm/migrate.c
> index 32fa72ba10b4..8fed2655f2e8 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -851,6 +851,8 @@ static int __buffer_migrate_folio(struct address_space *mapping,
>  		bool busy;
>  		bool invalidated = false;
>  
> +		VM_WARN_ON_ONCE(test_and_set_bit_lock(BH_Migrate,
> +						      &head->b_state));

Careful here. This breaks the logic with !CONFIG_DEBUG_VM.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR