linux-ext4 - Re: Re: [PATCH] ext4: release discard bio after sending discard commands

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Date:   Wed, 2 Aug 2017 10:18:34 +0200
From:   Jan Kara <jack@...e.cz>
To:     Daeho Jeong <daeho.jeong@...sung.com>
Cc:     Jan Kara <jack@...e.cz>, "jack@...e.com" <jack@...e.com>,
        "tytso@....edu" <tytso@....edu>,
        "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>
Subject: Re: Re: [PATCH] ext4: release discard bio after sending discard
 commands

On Tue 01-08-17 23:31:38, Daeho Jeong wrote:
> 
> > > We've changed the discard command handling into parallel manner.
> > > But, in this change, I forgot decreasing the usage count of the bio
> > > which was used to send discard request. I'm sorry about that.
> > > 
> > > Signed-off-by: Daeho Jeong <daeho.jeong@...sung.com>
> > > Fixes: a015434480dc ("ext4: send parallel discards on commit
> > > completions")
>  
> > Why do you think this is needed? submit_bio_wait() consumes the reference
> > that you've got from __blkdev_issue_discard()...
> >  
> >                                                                Honza
> 
> Hi Jan,
> 
> I thought like you, but submit_bio_wait() doesn't consume the reference
> of the bio and the bio cannot be released after the I/O has been completed.
> The caller of submit_bio_wait() should invoke bio_put() in person.
> You can see what we have to do after calling submit_bio_wait() in
> fs/crypto/bio.c.
> 
> Actually, in our device, I can see that the slab memory grows gradually
> because of the unreleased discard bios.

Ah, good point. I had a deeper look now and indeed submit_bio_wait() uses
it's own end_io function which does not drop the bio reference. So I
retract my objection and feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

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