linux-kernel - Re: [PATCH v3 7/8] ext4: Use rbtrees to manage PAs instead of inode i_prealloc

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Message-ID: <Y9zHkMx7w4Io0TTv@li-bb2b2a4c-3307-11b2-a85c-8fa5c3a69313.ibm.com>
Date:   Fri, 3 Feb 2023 14:06:56 +0530
From:   Ojaswin Mujoo <ojaswin@...ux.ibm.com>
To:     Jan Kara <jack@...e.cz>
Cc:     linux-ext4@...r.kernel.org, "Theodore Ts'o" <tytso@....edu>,
        Ritesh Harjani <riteshh@...ux.ibm.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        rookxu <brookxu.cn@...il.com>,
        Ritesh Harjani <ritesh.list@...il.com>
Subject: Re: [PATCH v3 7/8] ext4: Use rbtrees to manage PAs instead of inode
 i_prealloc_list

On Fri, Jan 27, 2023 at 03:43:12PM +0100, Jan Kara wrote:
> 
> Well, I think cond_resched() + goto retry would be OK here. We could also
> cycle the corresponding group lock which would wait for
> ext4_mb_discard_group_preallocations() to finish but that is going to burn
> the CPU even more than the cond_resched() + retry as we'll be just spinning
> on the spinlock. Sleeping is IMHO not warranted as the whole
> ext4_mb_discard_group_preallocations() is running under a spinlock anyway
> so it should better be a very short sleep.
> 
> Or actually I have one more possible solution: What the adjusting function
> is doing that it looks up PA before and after ac->ac_o_ex.fe_logical and
> trims start & end to not overlap these PAs. So we could just lookup these
> two PAs (ignoring the deleted state) and then just iterate from these with
> rb_prev() & rb_next() until we find not-deleted ones. What do you think? 

Hey Jan, 

Just thought I'd update you, I'm trying this solution out, and it looks
good but I'm hitting a few bugs in the implementation. Will update here
once I have it working correctly.

Regards,
Ojaswin