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Subject: Re: Partial direct-io loop regression in 5.17-rc
To:     Milan Broz <gmazyland@gmail.com>
Cc:     linux-block <linux-block@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Ondrej Kozina <okozina@redhat.com>
References: <feb7e4b4-1a6f-71a7-0cdd-fda547408bea@gmail.com>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <08e1dbde-b27c-fd99-294c-8e4715b92576@kernel.dk>
Date:   Fri, 4 Feb 2022 06:32:27 -0700
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On 2/4/22 2:22 AM, Milan Broz wrote:
> Hi Jens,
> 
> It seems that there is a regression in direct-io over loop for partial
> direct-io reads (or perhaps even for other situations).
> 
> If I run this code (loop over 6M file, dd direct-io read with 4M blocks)
> 
> IMG=tst.img
> LOOP=/dev/loop66
> 
> truncate -s 6M $IMG
> losetup $LOOP $IMG
> dd if=$LOOP of=/dev/null bs=4M iflag=direct
> losetup -d $LOOP
> 
> 
> on older kernel (<=5.16) it reads the whole file
>    6291456 bytes (6.3 MB, 6.0 MiB) copied, 0.201591 s, 31.2 MB/s
> 
> 
> while on 5.17-rc (tested on today/s Linus' git) it reads only the full blocks:
>    4194304 bytes (4.2 MB, 4.0 MiB) copied, 0.201904 s, 20.8 MB/s
> 
> No error reported, exit code is 0.

Can you try:

https://git.kernel.dk/cgit/linux-block/commit/?h=block-5.17&id=3e1f941dd9f33776b3df4e30f741fe445ff773f3

-- 
Jens Axboe