{"id":2231982,"url":"http://patchwork.ozlabs.org/api/1.1/patches/2231982/?format=json","web_url":"http://patchwork.ozlabs.org/project/glibc/patch/c80956cb80f1071b8691c6b2f22fe09a6d64256d.1777667949.git.ashamil435@gmail.com/","project":{"id":41,"url":"http://patchwork.ozlabs.org/api/1.1/projects/41/?format=json","name":"GNU C Library","link_name":"glibc","list_id":"libc-alpha.sourceware.org","list_email":"libc-alpha@sourceware.org","web_url":"","scm_url":"","webscm_url":""},"msgid":"","date":"2026-05-01T20:59:25","name":"hugepages: cache THP mode and page size [BZ #34083]","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"19cc49efe37320d2a8b1f7f5dc94f7718e7eb4eb","submitter":{"id":93241,"url":"http://patchwork.ozlabs.org/api/1.1/people/93241/?format=json","name":"Shamil Abdulaev","email":"ashamil435@gmail.com"},"delegate":null,"mbox":"http://patchwork.ozlabs.org/project/glibc/patch/c80956cb80f1071b8691c6b2f22fe09a6d64256d.1777667949.git.ashamil435@gmail.com/mbox/","series":[{"id":502496,"url":"http://patchwork.ozlabs.org/api/1.1/series/502496/?format=json","web_url":"http://patchwork.ozlabs.org/project/glibc/list/?series=502496","date":"2026-05-01T20:59:25","name":"hugepages: cache THP mode and page size [BZ #34083]","version":1,"mbox":"http://patchwork.ozlabs.org/series/502496/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/2231982/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2231982/checks/","tags":{},"headers":{"Return-Path":"","X-Original-To":["incoming@patchwork.ozlabs.org","libc-alpha@sourceware.org"],"Delivered-To":["patchwork-incoming@legolas.ozlabs.org","libc-alpha@sourceware.org"],"Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256\n header.s=20251104 header.b=pDL23jJr;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=sourceware.org\n (client-ip=38.145.34.32; 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Cache their results in rtld_global\nso the expensive THP probes are performed once per process.\n\nTested on x86_64-linux-gnu. No new test failures.\n\nSigned-off-by: Shamil Abdulaev \n---\n elf/dl-support.c | 6 +++\n sysdeps/generic/hugepages.h | 7 ++++\n sysdeps/generic/ldsodefs.h | 6 +++\n sysdeps/unix/sysv/linux/hugepages.c | 58 ++++++++++++++++++++++++-----\n 4 files changed, 68 insertions(+), 9 deletions(-)","diff":"diff --git a/elf/dl-support.c b/elf/dl-support.c\nindex 0508d6113b..ec77cb3e7a 100644\n--- a/elf/dl-support.c\n+++ b/elf/dl-support.c\n@@ -144,6 +144,12 @@ int _dl_inhibit_cache;\n /* All known directories in sorted order. */\n struct r_search_path_elem *_dl_all_dirs;\n \n+/* Cached Transparent Huge Page mode and page size. */\n+int _dl_thp_mode;\n+unsigned long int _dl_thp_pagesize;\n+int _dl_thp_mode_state;\n+int _dl_thp_pagesize_state;\n+\n /* All directories after startup. */\n struct r_search_path_elem *_dl_init_all_dirs;\n \ndiff --git a/sysdeps/generic/hugepages.h b/sysdeps/generic/hugepages.h\nindex 5fc9b5c8de..68be2ee242 100644\n--- a/sysdeps/generic/hugepages.h\n+++ b/sysdeps/generic/hugepages.h\n@@ -32,6 +32,13 @@ enum thp_mode_t\n thp_mode_not_supported\n };\n \n+enum thp_cache_state_t\n+{\n+ thp_cache_uninitialized,\n+ thp_cache_initializing,\n+ thp_cache_initialized\n+};\n+\n enum thp_mode_t __get_thp_mode (void) attribute_hidden;\n \n /* Return the supported huge page size from the REQUESTED sizes on PAGESIZE\ndiff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h\nindex 15c4659853..4b2e337a81 100644\n--- a/sysdeps/generic/ldsodefs.h\n+++ b/sysdeps/generic/ldsodefs.h\n@@ -395,6 +395,12 @@ struct rtld_global\n /* List of search directories. */\n EXTERN struct r_search_path_elem *_dl_all_dirs;\n \n+ /* Cached Transparent Huge Page mode and page size. */\n+ EXTERN int _dl_thp_mode;\n+ EXTERN unsigned long int _dl_thp_pagesize;\n+ EXTERN int _dl_thp_mode_state;\n+ EXTERN int _dl_thp_pagesize_state;\n+\n /* Get architecture specific definitions. */\n #define PROCINFO_DECL\n #ifndef PROCINFO_CLASS\ndiff --git a/sysdeps/unix/sysv/linux/hugepages.c b/sysdeps/unix/sysv/linux/hugepages.c\nindex 46e05151a3..c32127f6a4 100644\n--- a/sysdeps/unix/sysv/linux/hugepages.c\n+++ b/sysdeps/unix/sysv/linux/hugepages.c\n@@ -16,6 +16,8 @@\n License along with the GNU C Library; see the file COPYING.LIB. If\n not, see . */\n \n+#include \n+#include \n #include \n #include \n #include \n@@ -25,18 +27,32 @@\n unsigned long int\n __get_thp_size (void)\n {\n+ if (atomic_load_acquire (&GL (dl_thp_pagesize_state))\n+ == thp_cache_initialized)\n+ return GL (dl_thp_pagesize);\n+\n+ int state = thp_cache_uninitialized;\n+ if (!atomic_compare_exchange_acquire (&GL (dl_thp_pagesize_state),\n+\t\t\t\t\t&state, thp_cache_initializing))\n+ {\n+ while (atomic_load_acquire (&GL (dl_thp_pagesize_state))\n+\t != thp_cache_initialized)\n+\tatomic_spin_nop ();\n+ return GL (dl_thp_pagesize);\n+ }\n+\n+ unsigned long int r = 0;\n int fd = __open64_nocancel (\n \"/sys/kernel/mm/transparent_hugepage/hpage_pmd_size\", O_RDONLY);\n if (fd == -1)\n- return 0;\n+ goto out;\n \n char str[INT_BUFSIZE_BOUND (unsigned long int)];\n ssize_t s = __read_nocancel (fd, str, sizeof (str));\n __close_nocancel (fd);\n if (s < 0)\n- return 0;\n+ goto out;\n \n- unsigned long int r = 0;\n for (ssize_t i = 0; i < s; i++)\n {\n if (str[i] == '\\n')\n@@ -44,16 +60,36 @@ __get_thp_size (void)\n r *= 10;\n r += str[i] - '0';\n }\n+\n+out:\n+ GL (dl_thp_pagesize) = r;\n+ atomic_store_release (&GL (dl_thp_pagesize_state),\n+\t\t\tthp_cache_initialized);\n return r;\n }\n \n enum thp_mode_t\n __get_thp_mode (void)\n {\n+ if (atomic_load_acquire (&GL (dl_thp_mode_state))\n+ == thp_cache_initialized)\n+ return (enum thp_mode_t) GL (dl_thp_mode);\n+\n+ int state = thp_cache_uninitialized;\n+ if (!atomic_compare_exchange_acquire (&GL (dl_thp_mode_state),\n+\t\t\t\t\t&state, thp_cache_initializing))\n+ {\n+ while (atomic_load_acquire (&GL (dl_thp_mode_state))\n+\t != thp_cache_initialized)\n+\tatomic_spin_nop ();\n+ return (enum thp_mode_t) GL (dl_thp_mode);\n+ }\n+\n+ enum thp_mode_t mode = thp_mode_not_supported;\n int fd = __open64_nocancel (\"/sys/kernel/mm/transparent_hugepage/enabled\",\n \t\t\t O_RDONLY);\n if (fd == -1)\n- return thp_mode_not_supported;\n+ goto out;\n \n static const char mode_always[] = \"[always] madvise never\\n\";\n static const char mode_madvise[] = \"always [madvise] never\\n\";\n@@ -63,19 +99,23 @@ __get_thp_mode (void)\n ssize_t s = __read_nocancel (fd, str, sizeof (str));\n __close_nocancel (fd);\n if (s >= sizeof str || s < 0)\n- return thp_mode_not_supported;\n+ goto out;\n str[s] = '\\0';\n \n if (s == sizeof (mode_always) - 1)\n {\n if (strcmp (str, mode_always) == 0)\n-\treturn thp_mode_always;\n+\tmode = thp_mode_always;\n else if (strcmp (str, mode_madvise) == 0)\n-\treturn thp_mode_madvise;\n+\tmode = thp_mode_madvise;\n else if (strcmp (str, mode_never) == 0)\n-\treturn thp_mode_never;\n+\tmode = thp_mode_never;\n }\n- return thp_mode_not_supported;\n+\n+out:\n+ GL (dl_thp_mode) = mode;\n+ atomic_store_release (&GL (dl_thp_mode_state), thp_cache_initialized);\n+ return mode;\n }\n \n #if !IS_IN (rtld)\n","prefixes":[]}