There would be a benefit to doing fadvise POSIX_FADV_DONTNEED after
deep-scrub reads for objects not recently accessed by clients.
I see the NewStore objectstore sometimes using the O_DIRECT flag for
writes. This concerns me because the open(2) man pages says:
"Applications should avoid mixing O_DIRECT and normal I/O to the same
file, and especially to overlapping byte regions in the same file. Even
when the filesystem correctly handles the coherency issues in this
situation, overall I/O throughput is likely to be slower than using
either mode alone."
David
On 10/7/15 7:50 AM, Sage Weil wrote:
It's not, but it would not be ahrd to do this. There are fadvise-style
hints being passed down that could trigger O_DIRECT reads in this case.
That may not be the best choice, though--it won't use data that happens
to be in cache and it'll also throw it out..
On Wed, 7 Oct 2015, Pawe? Sadowski wrote:
Hi,
Can anyone tell if deep scrub is done using O_DIRECT flag or not? I'm
not able to verify that in source code.
If not would it be possible to add such feature (maybe config option) to
help keeping Linux page cache in better shape?
Thanks,
--
PS
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