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From:   Andreas Dilger <adilger@dilger.ca>
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Subject: Re: [RFC] replace revoke hash table with rhashtable
Date:   Wed, 1 Sep 2021 12:32:28 -0600
In-Reply-To: <96FE09AA-171C-49B1-B434-505C15FEB435@whamcloud.com>
Cc:     linux-ext4 <linux-ext4@vger.kernel.org>
To:     Alex Zhuravlev <azhuravlev@whamcloud.com>
References: <96FE09AA-171C-49B1-B434-505C15FEB435@whamcloud.com>
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On Aug 31, 2021, at 8:49 AM, Alex Zhuravlev <azhuravlev@whamcloud.com> =
wrote:
>=20
> Hi,
>=20
> Not so long ago we noticed that journal replay can take quite a lot =
(hours)
> in cases where many journaled blocks were freed during a short period.

It may be worthwhile to mention this was a case with a 4GB journal size.

> I benchmarked hash table used by revoke code, basically it=E2=80=99s =
lookup+insert
> like jbd2 does at replay:
>=20
> 1048576 records - 95 seconds
> 2097152 records - 580 seconds
>=20
> Then I benchmarked rhashtable:
> 1048576 records - 2 seconds
> 2097152 records - 3 seconds
> 4194304 records - 7 seconds
>=20
> So, here is a patch replacing existing fixed-size hash table with =
rhashtable, please have a look.
>=20
> Thanks, Alex

Alex,
the patch looks good from both a performance standpoint, as well as
a good reduction in lines (and possibly memory, for the cases where
there are fewer entries in the hash than the static table size).

I did notice some lines are using 8-space indents instead of tabs.
That can be fixed if there are any other comments, and you resubmit
without [RFC].

Cheers, Andreas


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