On 03-Feb-22 6:13 PM, Dmitry Kozlyuk wrote:
Hugepage mapping is a layer of EAL malloc builds upon.
There were implicit references to its details,
like mentions of segment file descriptors,
but no explicit description of its modes and operation.
Add an overview of mechanics used on ech supported OS.
Convert memory management subsections from list items
to level 4 headers: they are big and important enough.
Signed-off-by: Dmitry Kozlyuk <dkozl...@nvidia.com>
Acked-by: Bruce Richardson <bruce.richard...@intel.com>
---
+In dynamic memory mode, EAL removes a backing hugepage file
+when all pages mapped from it are freed back to the system.
+However, backing files may persist after the application terminates
+in case of a crash or a leak of DPDK memory (e.g. ``rte_free()`` is missing).
+This reduces the number of hugepages available to other processes
+as reported by ``/sys/kernel/mm/hugepages/hugepages-*/free_hugepages``.
+EAL can remove the backing files after opening them for mapping
+if ``--huge-unlink`` is given to avoid polluting hugetlbfs.
+However, since it disables multi-process anyway,
+using anonymous mapping (``--in-memory``) is recommended instead.
+
+:ref:`EAL memory allocator <malloc>` relies on hugepages being zero-filled.
+Hugepages are cleared by the kernel when a file in hugetlbfs or its part
+is mapped for the first time system-wide
+to prevent data leaks from previous users of the same hugepage.
+EAL ensures this behavior by removing existing backing files at startup
+and by recreating them before opening for mapping (as a precaution).
+
+Anonymous mapping does not allow multi-process architecture.
+This mode does not use hugetlbfs
+and thus does not require root permissions for memory management
+(the limit of locked memory amount, ``MEMLOCK``, still applies).
+It is free of filename conflict and leftover file issues.
+If memfd_create(2) is supported both at build and run time,
Nitpick, quote memfd? e.g. `memfd_create(2)`
Otherwise,
Acked-by: Anatoly Burakov <anatoly.bura...@intel.com>
--
Thanks,
Anatoly
