linux-ext4 - Re: [PATCH] jbd2: wake up journal waiters in FIFO order, not LIFO

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Date:   Thu, 8 Sep 2022 14:43:32 +0530
From:   "Ritesh Harjani (IBM)" <ritesh.list@...il.com>
To:     Alexey Lyashkov <alexey.lyashkov@...il.com>
Cc:     linux-ext4@...r.kernel.org, Theodore Ts'o <tytso@....edu>,
        Andreas Dilger <adilger@...ger.ca>,
        Artem Blagodarenko <artem.blagodarenko@...il.com>,
        Andrew Perepechko <anserper@...ru>
Subject: Re: [PATCH] jbd2: wake up journal waiters in FIFO order, not  LIFO

On 22/09/08 11:16AM, Ritesh Harjani (IBM) wrote:
> On 22/09/07 07:59PM, Alexey Lyashkov wrote:
> > From: Andrew Perepechko <anserper@...ru>
> > 
> > LIFO wakeup order is unfair and sometimes leads to a journal
> > user not being able to get a journal handle for hundreds of
> > transactions in a row.
> > 
> > FIFO wakeup can make things more fair.
> 
> prepare_to_wait() will always add the task to the head of the list.
> While prepare_to_wait_exclusive() will add the task to the tail since all of the
> exclusive tasks are added to the tail.
> wake_up() function will wake up all non-exclusive and single exclusive task 
> v/s
> wake_up_all() function will wake up all tasks irrespective.
> 
> So your change does makes the ordering to FIFO, in which the task which came in 
> first will be woken up first. 

With all other details which got discussed in other threads. 
This looks like the right thing to do.

Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@...il.com>