On 12/01/2017 05:35 AM, Thomas Munro wrote: >> since it also >> supports "transparent" hugepages. > Hmm. Yeah, it does, but apparently it's not so transparent.
+1. We saw performance drop with transparent_hugepage enabled on server with more than 256GB RAM. Access to the cache where slow down when kernel try to defragment pages. When that happens, we saw the function isolate_freepages_block appearing in most consuming function with perf top. Thanks to Marc Cousin analysis, putting "madvise" to /sys/kernel/mm/transparent_hugepage/enabled solved the problem. He also notice that THP only works for "anonymous memory mappings"[1] (shared_buffers are not anonymous). 1: https://www.kernel.org/doc/Documentation/vm/transhuge.txt Regards, -- Adrien NAYRAT
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