Re: [fuse-devel] [PATCH 1/2] [RFC for fuse-next ] fuse: DIO writes always use the same code path

[Bernd Schubert <bernd.schubert@fastmail.fm>]

On 8/24/23 06:32, Hao Xu wrote:
> 
> On 8/22/23 17:53, Miklos Szeredi via fuse-devel wrote:
>> On Mon, 21 Aug 2023 at 19:48, Bernd Schubert <bschubert@ddn.com> wrote:
>>> There were two code paths direct-io writes could
>>> take. When daemon/server side did not set FOPEN_DIRECT_IO
>>>      fuse_cache_write_iter -> direct_write_fallback
>>> and with FOPEN_DIRECT_IO being set
>>>      fuse_direct_write_iter
>>>
>>> Advantage of fuse_direct_write_iter is that it has optimizations
>>> for parallel DIO writes - it might only take a shared inode lock,
>>> instead of the exclusive lock.
>>>
>>> With commits b5a2a3a0b776/80e4f25262f9 the fuse_direct_write_iter
>>> path also handles concurrent page IO (dirty flush and page release),
>>> just the condition on fc->direct_io_relax had to be removed.
>>>
>>> Performance wise this basically gives the same improvements as
>>> commit 153524053bbb, just O_DIRECT is sufficient, without the need
>>> that server side sets FOPEN_DIRECT_IO
>>> (it has to set FOPEN_PARALLEL_DIRECT_WRITES), though.
>> Consolidating the various direct IO paths would be really nice.
>>
>> Problem is that fuse_direct_write_iter() lacks some code from
>> generic_file_direct_write() and also completely lacks
> 
> 
> I see, seems the page invalidation post direct write is needed
> 
> as well.
> 

I'm in the middle of verifying code paths, but I wonder if we can
remove the entire function at all.


https://github.com/bsbernd/linux/commit/fe082a0795fe5839211488e9645732b5f3809bea

on this branch

https://github.com/bsbernd/linux/commits/o-direct-shared-lock


Also totally untested - I hope I did not miss anything...


Thanks,
Bernd