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Re: [Qemu-devel] [RFC PATCH 09/16] qcow2: Move COW and L2 update into ow
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-devel] [RFC PATCH 09/16] qcow2: Move COW and L2 update into own coroutine |
Date: |
Tue, 18 Sep 2012 16:44:22 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:13.0) Gecko/20120605 Thunderbird/13.0 |
Am 18.09.2012 16:24, schrieb Paolo Bonzini:
> Il 18/09/2012 13:40, Kevin Wolf ha scritto:
>> + qemu_co_mutex_unlock(&s->lock);
>> + qemu_co_rwlock_rdlock(&s->l2meta_flush);
>
> Should this lock be taken in process_l2meta? It's a bit easier to follow.
I'm pretty sure there was a reason, but it isn't obvious any more. I
guess I should have put a comment there... Maybe it doesn't exist any
more, or maybe it's not that obvious.
The difference would be that while waiting for the lock, the original
write request could complete instead of waiting as well, and that the
lock is potentially taken only in a BH instead of immediately.
What happens if bdrv_aio_flush() and bdrv_aio_writev() are both in
flight? If the flush runs its stop_l2meta() after the write request has
signalled completion, but before the COW coroutine has started, it gets
the lock even though a COW must still be processed. I believe we could
then return a successful flush when the metadata isn't really on disk yet.
So if you agree, I think we need to leave it where it is.
Kevin
- [Qemu-devel] [RFC PATCH 04/16] qcow2: Drop l2meta.cluster_offset, (continued)
- [Qemu-devel] [RFC PATCH 04/16] qcow2: Drop l2meta.cluster_offset, Kevin Wolf, 2012/09/18
- [Qemu-devel] [RFC PATCH 07/16] qcow2: Factor out handle_dependencies(), Kevin Wolf, 2012/09/18
- [Qemu-devel] [RFC PATCH 06/16] qcow2: Enable dirty flag in qcow2_alloc_cluster_link_l2, Kevin Wolf, 2012/09/18
- [Qemu-devel] [RFC PATCH 05/16] qcow2: Allocate l2meta only for cluster allocations, Kevin Wolf, 2012/09/18
- [Qemu-devel] [RFC PATCH 12/16] qcow2: Handle dependencies earlier, Kevin Wolf, 2012/09/18
- [Qemu-devel] [RFC PATCH 14/16] qcow2: Execute run_dependent_requests() without lock, Kevin Wolf, 2012/09/18
- [Qemu-devel] [RFC PATCH 09/16] qcow2: Move COW and L2 update into own coroutine, Kevin Wolf, 2012/09/18
- [Qemu-devel] [RFC PATCH 13/16] qcow2: Change handle_dependency to byte granularity, Kevin Wolf, 2012/09/18
- [Qemu-devel] [RFC PATCH 11/16] qcow2: Add error handling to the l2meta coroutine, Kevin Wolf, 2012/09/18
- [Qemu-devel] [RFC PATCH 10/16] qcow2: Delay the COW, Kevin Wolf, 2012/09/18
- [Qemu-devel] [RFC PATCH 15/16] qcow2: Cancel COW when overwritten, Kevin Wolf, 2012/09/18