From: Ritesh Harjani <riteshh@linux.ibm.com>
To: Hillf Danton <hdanton@sina.com>
Cc: linux-ext4@vger.kernel.org, jack@suse.com, tytso@mit.edu,
Markus Elfring <Markus.Elfring@web.de>,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
Borislav Petkov <bp@alien8.de>,
Marek Szyprowski <m.szyprowski@samsung.com>,
syzbot+82f324bb69744c5f6969@syzkaller.appspotmail.com
Subject: Re: [PATCHv2 1/1] ext4: mballoc: Use this_cpu_read instead of this_cpu_ptr
Date: Wed, 10 Jun 2020 07:36:09 +0530 [thread overview]
Message-ID: <20200610020610.AEB3211C066@d06av25.portsmouth.uk.ibm.com> (raw)
In-Reply-To: <20200609123716.16888-1-hdanton@sina.com>
On 6/9/20 6:07 PM, Hillf Danton wrote:
>
> On Tue, 9 Jun 2020 18:53:23 +0800 Ritesh Harjani wrote:
>>
>> Simplify reading a seq variable by directly using this_cpu_read API
>> instead of doing this_cpu_ptr and then dereferencing it.
>
> Two of the quick questions
> 1) Why can blocks discarded in a ext4 FS help allocators in another?
I am not sure if I understand your Q correctly. But here is a brief
about the patchset. If there were PA blocks just or about to be
discarded by another thread, then the current thread who is doing block
allocation should not fail with ENOSPC error instead should be able to
allocate those blocks from another thread. The concept is better
explained in the commit msgs, if more details are required.
Without this patchset (in some heavy multi-threaded use case) allocation
was failing when the overall filesystem space available was more then 50%.
>
> 2) Why is a percpu seqcount prefered over what <linux/seqlock.h>
> can offer?
>
Since this could be a multi-threaded use case, per cpu variable helps in
avoid cache line bouncing problem, which could happen when the same
variable is updated by multiple threads on different cpus.
-ritesh
next parent reply other threads:[~2020-06-10 2:06 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20200609123716.16888-1-hdanton@sina.com>
2020-06-10 2:06 ` Ritesh Harjani [this message]
2020-06-09 10:53 [PATCHv2 1/1] ext4: mballoc: Use this_cpu_read instead of this_cpu_ptr Ritesh Harjani
2020-06-10 6:25 ` Christoph Hellwig
2020-06-10 6:34 ` Ritesh Harjani
2020-06-11 15:03 ` Theodore Y. Ts'o
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