hi, Raúl First, the most of the OS memory cache is used by Page Cache <https://en.wikipedia.org/wiki/Page_cache> which OS use for caching the recent read/write I/O.
I think the understanding of OS memory cache should be discussed in two different perspectives. From a perspective of user-space (e.g, Spark application), it is not used, since the Spark is not allocating memory from this part of memory. However, from a perspective of OS, it is actually used, because the memory pages are already allocated for caching the I/O pages. For each I/O request, the OS always allocate memory pages to cache it to expect these cached I/O pages can be reused in near future. Recall, you use vim/emacs to open a large file. It is pretty slow when you open it at the first time. But it will be much faster when you close it and open it immediately because the file has been cached in file cache at the first time you open it. It is hard for Spark to use this part of memory. Because this part of the memory is managed by OS and is transparent to applications. The only thing you can do is that you can continuously allocate memory from OS (by malloc()), to some certain points which the OS senses some memory pressure, the OS will voluntarily release the page cache to satisfy your memory allocation. Another thing is that the memory limit of Spark is limited by maximum JVM heap size. So your memory request from your Spark application is actually handled by JVM not the OS. Hope this answer can help you! Wei -- Sent from: http://apache-spark-user-list.1001560.n3.nabble.com/ --------------------------------------------------------------------- To unsubscribe e-mail: user-unsubscr...@spark.apache.org
