[PATCH v3 6/6] eal: extend --huge-unlink for hugepage file reuse

[Dmitry Kozlyuk <dkozlyuk@nvidia.com>]

Expose Linux EAL ability to reuse existing hugepage files
via --huge-unlink=never switch.
Default behavior is unchanged, it can also be specified
using --huge-unlink=existing for consistency.
Old --huge-unlink switch is kept,
it is an alias for --huge-unlink=always.
Add a test case for the --huge-unlink=never mode.

Signed-off-by: Dmitry Kozlyuk <dkozlyuk@nvidia.com>
Acked-by: Thomas Monjalon <thomas@monjalon.net>
---
 app/test/test_eal_flags.c                     | 25 ++++++++++++
 doc/guides/linux_gsg/linux_eal_parameters.rst | 24 ++++++++++--
 .../prog_guide/env_abstraction_layer.rst      | 13 +++++++
 doc/guides/rel_notes/release_22_03.rst        |  7 ++++
 lib/eal/common/eal_common_options.c           | 39 +++++++++++++++++--
 5 files changed, 101 insertions(+), 7 deletions(-)

diff --git a/app/test/test_eal_flags.c b/app/test/test_eal_flags.c
index d7f4c2cd47..e2696cda63 100644
--- a/app/test/test_eal_flags.c
+++ b/app/test/test_eal_flags.c
@@ -1122,6 +1122,11 @@ test_file_prefix(void)
 		DEFAULT_MEM_SIZE, "--single-file-segments",
 		"--file-prefix=" memtest1 };
 
+	/* primary process with memtest1 and --huge-unlink=never mode */
+	const char * const argv9[] = {prgname, "-m",
+		DEFAULT_MEM_SIZE, "--huge-unlink=never",
+		"--file-prefix=" memtest1 };
+
 	/* check if files for current prefix are present */
 	if (process_hugefiles(prefix, HUGEPAGE_CHECK_EXISTS) != 1) {
 		printf("Error - hugepage files for %s were not created!\n", prefix);
@@ -1290,6 +1295,26 @@ test_file_prefix(void)
 		return -1;
 	}
 
+	/* this process will run with --huge-unlink,
+	 * so it should not remove hugepage files when it exits
+	 */
+	if (launch_proc(argv9) != 0) {
+		printf("Error - failed to run with --huge-unlink=never\n");
+		return -1;
+	}
+
+	/* check if hugefiles for memtest1 are present */
+	if (process_hugefiles(memtest1, HUGEPAGE_CHECK_EXISTS) == 0) {
+		printf("Error - hugepage files for %s were deleted!\n",
+				memtest1);
+		return -1;
+	} else {
+		if (process_hugefiles(memtest1, HUGEPAGE_DELETE) != 1) {
+			printf("Error - deleting hugepages failed!\n");
+			return -1;
+		}
+	}
+
 	return 0;
 }
 
diff --git a/doc/guides/linux_gsg/linux_eal_parameters.rst b/doc/guides/linux_gsg/linux_eal_parameters.rst
index 74df2611b5..ea8f381391 100644
--- a/doc/guides/linux_gsg/linux_eal_parameters.rst
+++ b/doc/guides/linux_gsg/linux_eal_parameters.rst
@@ -84,10 +84,26 @@ Memory-related options
     Use specified hugetlbfs directory instead of autodetected ones. This can be
     a sub-directory within a hugetlbfs mountpoint.
 
-*   ``--huge-unlink``
-
-    Unlink hugepage files after creating them (implies no secondary process
-    support).
+*   ``--huge-unlink[=existing|always|never]``
+
+    No ``--huge-unlink`` option or ``--huge-unlink=existing`` is the default:
+    existing hugepage files are removed and re-created
+    to ensure the kernel clears the memory and prevents any data leaks.
+
+    With ``--huge-unlink`` (no value) or ``--huge-unlink=always``,
+    hugepage files are also removed before mapping them,
+    so that the application leaves no files in hugetlbfs.
+    This mode implies no multi-process support.
+
+    When ``--huge-unlink=never`` is specified, existing hugepage files
+    are never removed, but are remapped instead, allowing hugepage reuse.
+    This makes restart faster by saving time to clear memory at initialization,
+    but it may slow down zeroed allocations later.
+    Reused hugepages can contain data from previous processes that used them,
+    which may be a security concern.
+    Hugepage files created in this mode are also not removed
+    when all the hugepages mapped from them are freed,
+    which allows to reuse these files after a restart.
 
 *   ``--match-allocations``
 
diff --git a/doc/guides/prog_guide/env_abstraction_layer.rst b/doc/guides/prog_guide/env_abstraction_layer.rst
index b467bdf004..8f06c34c22 100644
--- a/doc/guides/prog_guide/env_abstraction_layer.rst
+++ b/doc/guides/prog_guide/env_abstraction_layer.rst
@@ -283,6 +283,18 @@ 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).
 
+One exception is ``--huge-unlink=never`` mode.
+It is used to speed up EAL initialization, usually on application restart.
+Clearing memory constitutes more than 95% of hugepage mapping time.
+EAL can save it by remapping existing backing files
+with all the data left in the mapped hugepages ("dirty" memory).
+Such segments are marked with ``RTE_MEMSEG_FLAG_DIRTY``.
+Memory allocator detects dirty segments and handles them accordingly,
+in particular, it clears memory requested with ``rte_zmalloc*()``.
+In this mode EAL also does not remove a backing file
+when all pages mapped from it are freed,
+because they are intended to be reusable at restart.
+
 Anonymous mapping does not allow multi-process architecture.
 This mode does not use hugetlbfs
 and thus does not require root permissions for memory management
@@ -959,6 +971,7 @@ to be virtually contiguous.
 *   dirty - this flag is only meaningful when ``state`` is ``FREE``.
     It indicates that the content of the element is not fully zero-filled.
     Memory from such blocks must be cleared when requested via ``rte_zmalloc*()``.
+    Dirty elements only appear with ``--huge-unlink=never``.
 
 *   pad - this holds the length of the padding present at the start of the block.
     In the case of a normal block header, it is added to the address of the end
diff --git a/doc/guides/rel_notes/release_22_03.rst b/doc/guides/rel_notes/release_22_03.rst
index 746f50e84f..58361db687 100644
--- a/doc/guides/rel_notes/release_22_03.rst
+++ b/doc/guides/rel_notes/release_22_03.rst
@@ -73,6 +73,13 @@ New Features
 
   The new API ``rte_event_eth_rx_adapter_event_port_get()`` was added.
 
+* **Added ability to reuse hugepages in Linux.**
+
+  It is possible to reuse files in hugetlbfs to speed up hugepage mapping,
+  which may be useful for fast restart and large allocations.
+  The new mode is activated with ``--huge-unlink=never``
+  and has security implications, refer to the user and programmer guides.
+
 
 Removed Items
 -------------
diff --git a/lib/eal/common/eal_common_options.c b/lib/eal/common/eal_common_options.c
index cdd2284b0c..45d393b393 100644
--- a/lib/eal/common/eal_common_options.c
+++ b/lib/eal/common/eal_common_options.c
@@ -74,7 +74,7 @@ eal_long_options[] = {
 	{OPT_FILE_PREFIX,       1, NULL, OPT_FILE_PREFIX_NUM      },
 	{OPT_HELP,              0, NULL, OPT_HELP_NUM             },
 	{OPT_HUGE_DIR,          1, NULL, OPT_HUGE_DIR_NUM         },
-	{OPT_HUGE_UNLINK,       0, NULL, OPT_HUGE_UNLINK_NUM      },
+	{OPT_HUGE_UNLINK,       2, NULL, OPT_HUGE_UNLINK_NUM      },
 	{OPT_IOVA_MODE,	        1, NULL, OPT_IOVA_MODE_NUM        },
 	{OPT_LCORES,            1, NULL, OPT_LCORES_NUM           },
 	{OPT_LOG_LEVEL,         1, NULL, OPT_LOG_LEVEL_NUM        },
@@ -1598,6 +1598,28 @@ available_cores(void)
 	return str;
 }
 
+#define HUGE_UNLINK_NEVER "never"
+
+static int
+eal_parse_huge_unlink(const char *arg, struct hugepage_file_discipline *out)
+{
+	if (arg == NULL || strcmp(arg, "always") == 0) {
+		out->unlink_before_mapping = true;
+		return 0;
+	}
+	if (strcmp(arg, "existing") == 0) {
+		/* same as not specifying the option */
+		return 0;
+	}
+	if (strcmp(arg, HUGE_UNLINK_NEVER) == 0) {
+		RTE_LOG(WARNING, EAL, "Using --"OPT_HUGE_UNLINK"="
+			HUGE_UNLINK_NEVER" may create data leaks.\n");
+		out->unlink_existing = false;
+		return 0;
+	}
+	return -1;
+}
+
 int
 eal_parse_common_option(int opt, const char *optarg,
 			struct internal_config *conf)
@@ -1739,7 +1761,10 @@ eal_parse_common_option(int opt, const char *optarg,
 
 	/* long options */
 	case OPT_HUGE_UNLINK_NUM:
-		conf->hugepage_file.unlink_before_mapping = true;
+		if (eal_parse_huge_unlink(optarg, &conf->hugepage_file) < 0) {
+			RTE_LOG(ERR, EAL, "invalid --"OPT_HUGE_UNLINK" option\n");
+			return -1;
+		}
 		break;
 
 	case OPT_NO_HUGE_NUM:
@@ -2070,6 +2095,12 @@ eal_check_common_options(struct internal_config *internal_cfg)
 			"not compatible with --"OPT_HUGE_UNLINK"\n");
 		return -1;
 	}
+	if (!internal_cfg->hugepage_file.unlink_existing &&
+			internal_cfg->in_memory) {
+		RTE_LOG(ERR, EAL, "Option --"OPT_IN_MEMORY" is not compatible "
+			"with --"OPT_HUGE_UNLINK"="HUGE_UNLINK_NEVER"\n");
+		return -1;
+	}
 	if (internal_cfg->legacy_mem &&
 			internal_cfg->in_memory) {
 		RTE_LOG(ERR, EAL, "Option --"OPT_LEGACY_MEM" is not compatible "
@@ -2202,7 +2233,9 @@ eal_common_usage(void)
 	       "  --"OPT_NO_TELEMETRY"   Disable telemetry support\n"
 	       "  --"OPT_FORCE_MAX_SIMD_BITWIDTH" Force the max SIMD bitwidth\n"
 	       "\nEAL options for DEBUG use only:\n"
-	       "  --"OPT_HUGE_UNLINK"       Unlink hugepage files after init\n"
+	       "  --"OPT_HUGE_UNLINK"[=existing|always|never]\n"
+	       "                      When to unlink files in hugetlbfs\n"
+	       "                      ('existing' by default, no value means 'always')\n"
 	       "  --"OPT_NO_HUGE"           Use malloc instead of hugetlbfs\n"
 	       "  --"OPT_NO_PCI"            Disable PCI\n"
 	       "  --"OPT_NO_HPET"           Disable HPET\n"
-- 
2.25.1