Question: Modifying kernel to handle all I/O requests without page cache

Question: Modifying kernel to handle all I/O requests without page cache

[Jianshen Liu]

Hi,

I am working on a project trying to evaluate the performance of a
workload running on a storage device. I don't want the benchmark
result depends on a specific platform (e.g., a platform with X GiB of
physical memory). Because it prevents people from reproducing the same
result on a different platform configuration. Think about you are
benchmarking a read-heavy workload, with data caching enabled you may
end up with just testing the performance of the system memory.

Currently, I'm thinking how to eliminate the cache effects created by
the page cache. Direct I/O is a good option for testing with a single
application but is not good for testing with unknown
applications/workloads. Therefore, it is not feasible to ask people to
modify the application source code before running the benchmark.

Making changes within the kernel may only be the option because it is
transparent to all user-space applications. The problem is I don't
know how to modify the kernel so that it does not use the page cache
for any IOs to a specific storage device. I have tried to append a
fadvise64() call with POSIX_FADV_DONTNEED to the end of each
read/write system calls. The performance of this approach is far from
using Direct I/O. It is also unable to eliminate the caching effects
under concurrent I/Os. I'm looking for any advice here to point me an
efficient way to remove the cache effects from the page cache.

Thanks,
Jianshen