linux-kernel - Re: Partial direct-io loop regression in 5.17-rc

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Message-ID: <65bfe3d6-504c-8fba-2bf4-541ab24b324b@kernel.dk>
Date:   Fri, 4 Feb 2022 08:33:47 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     Milan Broz <gmazyland@...il.com>
Cc:     linux-block <linux-block@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ondrej Kozina <okozina@...hat.com>
Subject: Re: Partial direct-io loop regression in 5.17-rc

On 2/4/22 8:03 AM, Milan Broz wrote:
> 
> 
> On 04/02/2022 14:32, Jens Axboe wrote:
>> 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
> 
> Yes, it works now.
> (Not sure why I did not check if this patch is mainline, as I know
> about it. My bad...)
> 
> So this is going to some next rc, right?

Yes, it'll be in -rc3, pushing it out today or tomorrow.

-- 
Jens Axboe