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Re: [Qemu-block] [Qemu-devel] [PATCH v2 6/7] block/backup: teach backup_
Re: [Qemu-block] [Qemu-devel] [PATCH v2 6/7] block/backup: teach backup_cow_with_bounce_buffer to copy more at once
Sat, 10 Aug 2019 12:54:49 +0000
10.08.2019 15:47, Eric Blake wrote:
> On 8/10/19 7:12 AM, Vladimir Sementsov-Ogievskiy wrote:
>> 09.08.2019 18:59, Eric Blake wrote:
>>> On 8/9/19 10:32 AM, Vladimir Sementsov-Ogievskiy wrote:
>>>> backup_cow_with_offload can transfer more than on cluster. Let
>>>> backup_cow_with_bounce_buffer behave similarly. It reduces number
>>>> of IO and there are no needs to copy cluster by cluster.
>>> It reduces the number of IO requests, since there is no need to copy
>>> cluster by cluster.
>>>> - bool *error_is_read,
>>>> - void
>>>> + bool *error_is_read)
>>> Why is this signature changing?
>> 2. Actually it is a question about memory allocator: is it fast and optimized
>> enough to not care, or is it bad, and we should work-around it like in
>> mirror? And in my opinion (proved by a bit of benchmarking) memalign
>> is fast enough to don't care. I was answering similar question in more
>> and with some numbers here:
>> So, I'd prefere to not care and keep code simpler. But if you don't agree,
>> I can leave shared buffer here, at least until introduction of parallel
>> Then, it will be something like qemu_try_blockalign(MIN(bytes, 64M))..
> It may still be worth capping at 64M. I'm not opposed to a change to
> per-request allocation rather than trying to reuse a buffer, if it is
> going to make parallelization efforts easier; but I am worried about the
> maximum memory usage. I'm more worried that you are trying to cram two
> distinct changes into one patch, and didn't even mention the change
> about a change from buffer reuse to per-request allocations, in the
> commit message. If you make that sort of change, it should be called
> out in the commit message as intentional, or maybe even split to a
> separate patch.
OK, I failed to hide it :) Will split out and add 64M limit.
[Qemu-block] [PATCH v2 4/7] block/backup: drop handling of max_transfer for copy_range, Vladimir Sementsov-Ogievskiy, 2019/08/09
[Qemu-block] [PATCH v2 2/7] block/backup: refactor write_flags, Vladimir Sementsov-Ogievskiy, 2019/08/09
[Qemu-block] [PATCH v2 1/7] block/backup: deal with zero detection, Vladimir Sementsov-Ogievskiy, 2019/08/09
[Qemu-block] [PATCH v2 7/7] block/backup: merge duplicated logic into backup_do_cow, Vladimir Sementsov-Ogievskiy, 2019/08/09
Re: [Qemu-block] [PATCH v2 0/7] backup improvements, Vladimir Sementsov-Ogievskiy, 2019/08/09