From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
To: Max Reitz <mreitz@redhat.com>, qemu-block@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>,
Anton Nefedov <anton.nefedov@virtuozzo.com>,
qemu-devel@nongnu.org, qemu-stable@nongnu.org,
Stefan Hajnoczi <stefanha@redhat.com>,
"Denis V . Lunev" <den@openvz.org>
Subject: Re: [PATCH for-4.2 v2 3/3] block/file-posix: Let post-EOF fallocate serialize
Date: Sat, 22 Aug 2020 20:04:56 +0300 [thread overview]
Message-ID: <de210b71-47e9-e119-3ab9-1dbf0812a4b6@virtuozzo.com> (raw)
In-Reply-To: <d85c544c-70c0-6860-0b5c-a2d46d740d1c@virtuozzo.com>
22.08.2020 20:03, Vladimir Sementsov-Ogievskiy wrote:
> 01.11.2019 18:25, Max Reitz wrote:
>> The XFS kernel driver has a bug that may cause data corruption for qcow2
>> images as of qemu commit c8bb23cbdbe32f. We can work around it by
>> treating post-EOF fallocates as serializing up until infinity (INT64_MAX
>> in practice).
>
> Hi! I'm doing some investigation, and here is an interesting result:
>
> Consider the following test:
>
> img=/ssd/x.qcow2; ./qemu-img create -f qcow2 $img 16G; ./qemu-img bench -c 50000 -d 64 -f qcow2 -o 1k -s 64k -t none -w $img
>
>
> Bisecting results changes between 2.12 and 5.1, I found the following:
>
> 2.12: ~20s
>
> ....
>
> c8bb23cbdbe32 "qcow2: skip writing zero buffers to empty COW areas" -> becomes ~12s [1]
>
> ....
>
>
> 292d06b925b27 "block/file-posix: Let post-EOF fallocate serialize" -> becomes ~9s [2]
>
> ....
>
> v5.1 ~9s
>
>
> And [1] is obvious, it is the main purpose of c8bb23cbdbe32. But [2] is a surprise for me.. Any ideas?
>
> ===
>
> just to check: staying at c8bb23cbdbe32 I revert c8bb23cbdbe32 and get again ~19.7s. So [2] doesn't substitute [1].
>
Note, it's all ext4.
--
Best regards,
Vladimir
next prev parent reply other threads:[~2020-08-22 17:05 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-01 15:25 [PATCH for-4.2 v2 0/3] qcow2: Fix data corruption on XFS Max Reitz
2019-11-01 15:25 ` [PATCH for-4.2 v2 1/3] block: Make wait/mark serialising requests public Max Reitz
2019-11-01 15:25 ` [PATCH for-4.2 v2 2/3] block: Add bdrv_co_get_self_request() Max Reitz
2019-11-01 15:25 ` [PATCH for-4.2 v2 3/3] block/file-posix: Let post-EOF fallocate serialize Max Reitz
2019-11-14 16:27 ` Christoph Hellwig
2019-11-14 17:15 ` Max Reitz
2019-11-14 17:16 ` Max Reitz
2020-06-02 14:43 ` Vladimir Sementsov-Ogievskiy
2020-06-02 15:46 ` Max Reitz
2020-06-02 16:16 ` Vladimir Sementsov-Ogievskiy
2020-06-02 16:38 ` Max Reitz
2020-06-02 17:01 ` Vladimir Sementsov-Ogievskiy
2020-06-02 17:08 ` Vladimir Sementsov-Ogievskiy
2020-08-22 17:03 ` Vladimir Sementsov-Ogievskiy
2020-08-22 17:04 ` Vladimir Sementsov-Ogievskiy [this message]
2020-08-26 8:23 ` Vladimir Sementsov-Ogievskiy
2020-08-26 11:20 ` Vladimir Sementsov-Ogievskiy
2019-11-01 15:48 ` [PATCH for-4.2 v2 0/3] qcow2: Fix data corruption on XFS no-reply
2019-11-04 8:29 ` Max Reitz
2019-11-04 9:09 ` Max Reitz
2019-11-04 9:45 ` Stefan Hajnoczi
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