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

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Message-ID: <zbcvnyipzfzvcoaboldo6dbms3ppoi4mm65havqtknzi3iviwe@of5gwmgs6kpd>
Date: Mon, 14 Apr 2025 14:12:42 +0200
From: Jan Kara <jack@...e.cz>
To: Davidlohr Bueso <dave@...olabs.net>
Cc: Jan Kara <jack@...e.cz>, Luis Chamberlain <mcgrof@...nel.org>, 
	brauner@...nel.org, tytso@....edu, adilger.kernel@...ger.ca, 
	linux-ext4@...r.kernel.org, riel@...riel.com, 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 Thu 10-04-25 10:30:28, Davidlohr Bueso wrote:
> On Thu, 10 Apr 2025, Jan Kara wrote:
> 
> > > @@ -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.
> 
> Ok, I guess just a WARN_ON_ONCE() here then.

Or just:

	bool migrating = test_and_set_bit_lock(BH_Migrate, &head->b_state);

	VM_WARN_ON_ONCE(migrating);

Frankly, I find statements with side-effects in WARN_ON / BUG_ON statements
rather confusing practice...

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