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

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On 8/24/23 11:43, Bernd Schubert wrote:


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@xxxxxxx> 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.

Sorry, doesn't remove fuse_direct_io(), but would go via generic_file_direct_write, which already has page invalidation.



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



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