Hi Bernd,
On 5/2/23 15:37, Bernd Schubert wrote:
Hi Hao,
On 5/2/23 09:28, Hao Xu wrote:
Hi all,
From discussion with Bernd, I get that FOPEN_DIRECT_IO is designed
for those user cases where users want strong coherency like network
filesystems, where one server serves multiple remote clients. And
thus shared mmap is disabled since local page cache existence breaks
this kind of coherency.
But here our use case is one virtiofs daemon serve one guest vm, We
use FOPEN_DIRECT_IO to reduce memory footprint not for coherency. So
we expect shared mmap works in this case. Here I suggest/am
implementing adding another flag to indicate this kind of
cases----use FOPEN_DIRECT_IO not for coherency----so that shared mmap
works.
Yeah it should work, but I think what you want is "DAX" - can you try
to enable it?
fuse_i.h: FUSE_DAX_ALWAYS, /* "-o dax=always" */
fuse_i.h: FUSE_DAX_NEVER, /* "-o dax=never" */
fuse_i.h: FUSE_DAX_INODE_USER, /* "-o dax=inode" */
Hope it helps,
Bernd
Thanks for your suggestion, the thing is most IO in our case are small
random read to small files. I believe Dax should help but doubt it may
be not too much.
Another reason we are not leveraging DAX is the hypervisor software we
use doesn't support DAX well. So I think the feature in this RFC should
be good for
some non-DAX use cases (like ours)
Thanks,
Hao
