Re: [PATCH] fuse: avoid unnecessary spinlock bump

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On 4/8/22 7:25 PM, Vivek Goyal wrote:
> On Fri, Apr 08, 2022 at 10:36:40AM +0800, JeffleXu wrote:
>>
>>
>> On 4/7/22 10:10 PM, Vivek Goyal wrote:
>>> On Sat, Apr 02, 2022 at 06:32:50PM +0800, Jeffle Xu wrote:
>>>> Move dmap free worker kicker inside the critical region, so that extra
>>>> spinlock lock/unlock could be avoided.
>>>>
>>>> Suggested-by: Liu Jiang <gerry@xxxxxxxxxxxxxxxxx>
>>>> Signed-off-by: Jeffle Xu <jefflexu@xxxxxxxxxxxxxxxxx>
>>>
>>> Looks good to me. Have you done any testing to make sure nothing is
>>> broken.
>>
>> xfstests -g quick shows no regression. The tested virtiofs is mounted
>> with "dax=always".
> 
> I think xfstests might not trigger reclaim. You probably will have to
> run something like blogbench with a small dax window like 1G so that
> heavy reclaim happens.


Actually, I configured the DAX window to 8MB, i.e. 4 slots when running
xfstests. Thus I think the reclaim path is most likely triggered.


> 
> For fun, I sometimes used to run it with a window of just say 16 dax
> ranges so that reclaim was so heavy that if there was a bug, it will
> show up.
> 

Yeah, my colleague had ever reported that a DAX window of 4KB will cause
hang in our internal OS (which is 4.19, we back ported virtiofs to
4.19). But then I found that this issue doesn't exist in the latest
upstream. The reason seems that in the upstream kernel,
devm_memremap_pages() called in virtio_fs_setup_dax() will fail directly
since the dax window (4KB) is not aligned with the sparse memory section.

-- 
Thanks,
Jeffle



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