linux-ext4 - Re: [PATCHv5 3/5] ext4: mballoc: Introduce pcpu seqcnt for freeing PA to improve ENOSPC handling

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Message-ID: <69a26eb8-e439-6574-6f46-e557d6c852d5@gmail.com>
Date:   Tue, 9 Jun 2020 16:07:41 +0530
From:   Ritesh Harjani <ritesh.list@...il.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        Ritesh Harjani <riteshh@...ux.ibm.com>,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Jan Kara <jack@...e.com>, Theodore Ts'o <tytso@....edu>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv5 3/5] ext4: mballoc: Introduce pcpu seqcnt for freeing PA
 to improve ENOSPC handling



On 6/9/20 3:50 PM, Borislav Petkov wrote:
> On Wed, Jun 03, 2020 at 03:40:16PM +0530, Ritesh Harjani wrote:
>> Yes, this is being discussed in the community.
>> I have submitted a patch which should help fix this warning msg.
>> Feel free to give this a try on your setup.
>>
>> https://marc.info/?l=linux-ext4&m=159110574414645&w=2
> 
> I just triggered the same thing here too. Looking at your fix and not
> even pretending to know what's going on with that percpu sequence
> counting, I can't help but wonder why do you wanna do:
> 
> 	seq = *raw_cpu_ptr(&discard_pa_seq);
> 
> instead of simply doing:
> 
> 	seq = this_cpu_read(discard_pa_seq);
> 

That's correct. Thanks for pointing that out.
I guess in my development version of code I had seq as a u64 pointer
variable which later I had changed to u64 variable but I guess I
continued using pcpu ptr APIs for that.

Let me re-submit that patch with your Suggested-by tag and corresponding
changes.

-riteshh