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Subject: Re: [powerpc][5.13.0-next-20210701] Kernel crash while running
 ltp(chdir01) tests
To:     Theodore Ts'o <tytso@mit.edu>
CC:     Jan Kara <jack@suse.cz>, <linuxppc-dev@lists.ozlabs.org>,
        Guoqing Jiang <guoqing.jiang@linux.dev>,
        Sachin Sant <sachinp@linux.vnet.ibm.com>,
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        "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>
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 <36778615-86fd-9a19-9bc9-f93a6f2d5817@huawei.com> <YN/a70ucYXu0DqGf@mit.edu>
From:   Zhang Yi <yi.zhang@huawei.com>
Message-ID: <66fb56cd-f1ff-c592-0202-0691372e32f5@huawei.com>
Date:   Sat, 3 Jul 2021 12:55:09 +0800
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On 2021/7/3 11:35, Theodore Ts'o wrote:
> On Sat, Jul 03, 2021 at 11:05:07AM +0800, Zhang Yi wrote:
>>
>> Originally, I want to add this shrinker as a optional feature for jbd2 because
>> only ext4 use it now and I'm not sure does ocfs2 needs this feature. So I export
>> jbd2_journal_[un]register_shrinker(), ext4 could invoke them individually.
> 
> The reason why bdev_try_to_free_page() callback was needed for ext4
> --- namely so there was a way to release checkpointed buffers under
> memory pressure --- also exists for ocfs2.  It was probably true that
> in most deployments of ocfs2, they weren't running with super-tight
> memory availability, so it may not have been necessary the same way
> that it might be necessary, say, if ext4 was being used on a Rasberry
> Pi.  :-)
> 
>> And one more thing we to could do is rename the 'j_jh_shrink_count' to something
>> like 'j_checkpoint_jh_count' because we always init it no matter we register the
>> shrinker or not later.
> 
> That makes sense.
> 
> In fact, unless I'm mistaken, I don't think it's legal to call
> percpu_counter_{inc,dec} if the shrinker isn't initialized.  So for
> ocfs2, if we didn't initialize percpu_counter, when
> __jbd2_journal_insert_checkpoint() tries to call percpu_counter_inc(),
> I believe things would potentially go *boom* on some implementations
> of the percpu counter (e.g., on Power and ARM).  So not only would it
> not hurt to register the shrinker for ocfs2, I think it's required.
> 
> So yeah, let's rename it to something like j_checkpoint_jh_count, and
> then let's inline jbd2_journal_[un]register_shrinker() in
> journal_init_common() and jbd2_journal_unregister_shrinker().
> 
> What do you think?
> 

Yeah, it sounds good to me. Do you want me to send the fix patch, or you
modify your commit 8f9e16badb8fd in another email directly?

Thanks,
Yi.