linux-ext4 - RE: Re: [PATCH] ext4: Remove expensive flush on fast commit

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Date:   Fri, 08 Jan 2021 11:37:07 +0900
From:   Daejun Park <daejun7.park@...sung.com>
To:     Andreas Dilger <adilger@...ger.ca>,
        Daejun Park <daejun7.park@...sung.com>,
        harshad shirwadkar <harshadshirwadkar@...il.com>
CC:     "tytso@....edu" <tytso@....edu>,
        "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: Re: [PATCH] ext4: Remove expensive flush on fast commit

> > In the fast commit, it adds REQ_FUA and REQ_PREFLUSH on each fast commit
> > block when barrier is enabled. However, in recovery phase, ext4 compares
> > CRC value in the tail. So it is sufficient adds REQ_FUA and REQ_PREFLUSH
> > on the block that has tail.
> 
> Does the tail block *always* contain a CRC, or is that dependent on
> EXT4_FEATURE_RO_COMPAT_METADATA_CSUM, JBD2_FEATURE_INCOMPAT_CSUM_V2,
> or JBD2_FEATURE_INCOMPAT_CSUM_V3 being enabled?

In the fast commit, the tail block always contain a CRC.
 
> If one of those features is *required* before the FAST_COMMIT feature
> can be used, then this patch looks OK.  Otherwise, the CSUM feature
> should be checked before the FUA is skipped for non-tail blocks.

So, I think it is OK without checking other CSUM feature.

Thanks,
Daejun