Ceph-fuse single read limitation?‏‏

[Z Zhang <zhangz.david@xxxxxxxxxxx>]

Hi Guys,
 
Now we have a very small cluster with 3 OSDs but using 40Gb NIC. We use ceph-fuse as cephfs client and enable readahead, 
but testing single reading a large file from cephfs via fio, dd or cp can only achieve ~70+MB/s, even if fio or dd's block size is set to 1MB or 4MB.
 
From the ceph client log, we found each read request's size (ll_read) is limited to 128KB, 
which should be the limitation of kernel fuse's FUSE_MAX_PAGES_PER_REQ = 32. 

We may try to increase this value to see the performance difference, but are there other options we can try to increase single read performance?

Thanks.
Zhi Zhang (David)

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