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From: David Sterba <dsterba@suse.cz>
To: Anand Jain <anand.jain@oracle.com>
Cc: dsterba@suse.cz, David Sterba <dsterba@suse.com>,
	linux-btrfs@vger.kernel.org
Subject: Re: [PATCH 3/6] btrfs: introduce try-lock semantics for exclusive op start
Date: Mon, 31 May 2021 20:23:41 +0200	[thread overview]
Message-ID: <20210531182341.GB31483@twin.jikos.cz> (raw)
In-Reply-To: <e17818ca-aef9-36b9-7677-cc49f24ea21e@oracle.com>

On Sat, May 29, 2021 at 09:48:46PM +0800, Anand Jain wrote:
> On 28/05/2021 20:30, David Sterba wrote:
> > On Thu, May 27, 2021 at 03:43:46PM +0800, Anand Jain wrote:
> >> On 21/05/2021 20:06, David Sterba wrote:
> > The code flow is the same.
> > 
> 
> Oh. Ok, now I understand your POV.
> 
> I looked up the document to check what it says, and it matched with
> my understanding too, as below.
> 
> https://www.kernel.org/doc/htmldocs/kernel-locking/trylock-functions.html
> -----
> ::
> They can be used if you need no access to the data protected with the 
> lock when some other thread is holding the lock.
> ::
> ----
> 
> Mainly ...trylocks are non-blocking/non-waiting locks.
> 
> However, btrfs_exclop_start_try_lock() can be blocking.

I see, the blocking is there. It should be unnoticeable in practice as
it's locking only a few instructions. The semantics is slighly different
than a plain lock as it needs to check if the exclusive operation is
locked, not the lock itself. If it had to be a true nonblocking trylock,
it would have to check the exclusive_operation value unlocked and either
bail if it's different or recheck it again under lock. This sounds more
complicated than we need.

  reply	other threads:[~2021-05-31 18:26 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-21 12:06 [PATCH 0/6] Support resize and device delete cancel ops David Sterba
2021-05-21 12:06 ` [PATCH 1/6] btrfs: protect exclusive_operation by super_lock David Sterba
2021-05-21 13:37   ` Josef Bacik
2021-05-21 12:06 ` [PATCH 2/6] btrfs: add cancelable chunk relocation support David Sterba
2021-05-21 13:21   ` Josef Bacik
2021-05-26 22:56     ` David Sterba
2021-06-16 13:54   ` Filipe Manana
2021-06-16 13:55     ` Filipe Manana
2021-06-16 15:53       ` David Sterba
2021-06-16 15:58       ` [PATCH v2] btrfs: add cancellable " David Sterba
2021-06-17  9:18         ` Filipe Manana
2021-05-21 12:06 ` [PATCH 3/6] btrfs: introduce try-lock semantics for exclusive op start David Sterba
2021-05-21 13:38   ` Josef Bacik
2021-05-27  7:43   ` Anand Jain
2021-05-28 12:30     ` David Sterba
2021-05-29 13:48       ` Anand Jain
2021-05-31 18:23         ` David Sterba [this message]
2021-05-21 12:06 ` [PATCH 4/6] btrfs: add wrapper for conditional start of exclusive operation David Sterba
2021-05-21 13:29   ` Josef Bacik
2021-05-21 16:45     ` David Sterba
2021-05-26 22:24       ` David Sterba
2021-05-21 12:06 ` [PATCH 5/6] btrfs: add cancelation to resize David Sterba
2021-05-21 13:38   ` Josef Bacik
2021-05-21 12:06 ` [PATCH 6/6] btrfs: add device delete cancel David Sterba
2021-05-21 13:38   ` Josef Bacik
2021-05-21 12:06 ` [PATCH 1/2] btrfs-progs: device remove: add support for cancel David Sterba
2021-05-21 12:06 ` [PATCH 2/2] btrfs-progs: fi resize: " David Sterba
2021-12-14 14:49 ` [PATCH 0/6] Support resize and device delete cancel ops Anand Jain
2021-12-15 15:13   ` David Sterba

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