From: Christoph Hellwig <hch@infradead.org>
To: Chao Yu <chao@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>,
jaegeuk@kernel.org, linux-f2fs-devel@lists.sourceforge.net,
linux-kernel@vger.kernel.org, linux-block@vger.kernel.org
Subject: Re: [PATCH v3] f2fs: introduce flush_policy sysfs entry
Date: Tue, 12 Aug 2025 00:59:10 -0700 [thread overview]
Message-ID: <aJr0Tk36ZNiCg8mQ@infradead.org> (raw)
In-Reply-To: <dec5b832-53f1-4274-902c-418f01df9458@kernel.org>
On Tue, Aug 12, 2025 at 03:53:54PM +0800, Chao Yu wrote:
> > What did you use before? At least for older qemu the default was
> > buffered I/O, which can lead to very expensive fua or flush calls.
>
> Previously, I didn't use any cache= option, as manual described, it
> should equal to cache=wrteback.
Modern qemu actually split the cache option. You absolute want
cache.direct=on. If you don't do simulated power fail testing by
killing qemu (or run real workloads for the matter, but who does that
:)) it might make sense to just ignore the flushes with cache.no-flush=on
as well, which is what I do for my test VMs on the laptop.
WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@infradead.org>
To: Chao Yu <chao@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>,
jaegeuk@kernel.org, linux-block@vger.kernel.org,
linux-kernel@vger.kernel.org,
linux-f2fs-devel@lists.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH v3] f2fs: introduce flush_policy sysfs entry
Date: Tue, 12 Aug 2025 00:59:10 -0700 [thread overview]
Message-ID: <aJr0Tk36ZNiCg8mQ@infradead.org> (raw)
In-Reply-To: <dec5b832-53f1-4274-902c-418f01df9458@kernel.org>
On Tue, Aug 12, 2025 at 03:53:54PM +0800, Chao Yu wrote:
> > What did you use before? At least for older qemu the default was
> > buffered I/O, which can lead to very expensive fua or flush calls.
>
> Previously, I didn't use any cache= option, as manual described, it
> should equal to cache=wrteback.
Modern qemu actually split the cache option. You absolute want
cache.direct=on. If you don't do simulated power fail testing by
killing qemu (or run real workloads for the matter, but who does that
:)) it might make sense to just ignore the flushes with cache.no-flush=on
as well, which is what I do for my test VMs on the laptop.
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next prev parent reply other threads:[~2025-08-12 7:59 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-08-07 3:48 [f2fs-dev] [PATCH v3] f2fs: introduce flush_policy sysfs entry Chao Yu via Linux-f2fs-devel
2025-08-07 3:48 ` Chao Yu
2025-08-07 5:31 ` [f2fs-dev] " Zhiguo Niu
2025-08-07 5:31 ` Zhiguo Niu
2025-08-11 10:52 ` Christoph Hellwig
2025-08-11 10:52 ` [f2fs-dev] " Christoph Hellwig
2025-08-11 13:44 ` Bart Van Assche
2025-08-11 13:44 ` [f2fs-dev] " Bart Van Assche via Linux-f2fs-devel
2025-08-12 6:39 ` Chao Yu
2025-08-12 6:39 ` [f2fs-dev] " Chao Yu via Linux-f2fs-devel
2025-08-12 6:28 ` Chao Yu
2025-08-12 6:28 ` [f2fs-dev] " Chao Yu via Linux-f2fs-devel
2025-08-12 7:32 ` Christoph Hellwig
2025-08-12 7:32 ` [f2fs-dev] " Christoph Hellwig
2025-08-12 7:53 ` Chao Yu
2025-08-12 7:53 ` [f2fs-dev] " Chao Yu via Linux-f2fs-devel
2025-08-12 7:59 ` Christoph Hellwig [this message]
2025-08-12 7:59 ` Christoph Hellwig
2025-08-12 8:22 ` Chao Yu
2025-08-12 8:22 ` [f2fs-dev] " Chao Yu via Linux-f2fs-devel
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