HugePages として確保したサイズは使用されていなくても free コマンドで見ると used に計上されると聞いたので理由を調べてみた。
Pages that are used as huge pages are reserved inside the kernel and cannot be used for other purposes. Huge pages cannot be swapped out under memory pressure.
Once a number of huge pages have been pre-allocated to the kernel huge page pool, a user with appropriate privilege can use either the mmap system call or shared memory system calls to use the huge pages
https://www.kernel.org/doc/Documentation/vm/hugetlbpage.txt
OSカーネル内に確保されるようだ。
[root@yazekats-linux linux]# free total used free shared buffers cached Mem: 16158544 3976420 12182124 0 148008 2649148 -/+ buffers/cache: 1179264 14979280 Swap: 8085500 0 8085500 [root@yazekats-linux linux]# sysctl -w vm.nr_hugepages=100 vm.nr_hugepages = 100 [root@yazekats-linux linux]# free total used free shared buffers cached Mem: 16158544 4180864 11977680 0 148060 2649436 -/+ buffers/cache: 1383368 14775176 Swap: 8085500 0 8085500 [root@yazekats-linux linux]# expr 1383368 - 1179264 204104
確かに vm.nr_hugepages に 100 を設定してみると、200MBほど used が増えた。
free コマンドはどこから情報をとっているかというと、
yazekats% strace -e open free ... open("/sys/devices/system/cpu/online", O_RDONLY|O_CLOEXEC) = 3 open("/proc/meminfo", O_RDONLY) = 3 total used free shared buffers cached Mem: 16158544 3982292 12176252 0 149808 2650748 -/+ buffers/cache: 1181736 14976808 Swap: 8085500 0 8085500
やはり /proc/meminfo を見ていますね。
free コマンドを含む RPM パッケージを調べて、
yazekats% rpm -qf `which free` procps-3.2.8-25.el6.x86_64
ソースをダウンロードして、
[root@yazekats-linux src]# cd /usr/local/src [root@yazekats-linux src]# wget http://procps.sourceforge.net/procps-3.2.8.tar.gz [root@yazekats-linux src]# tar xfvz procps-3.2.8.tar.gz
中身を見てみる
- /usr/local/src/procps-3.2.8/free.c
// free.c - free(1) // procps utility to display free memory information // // All new, Robert Love <rml@tech9.net> 18 Nov 2002 // Original by Brian Edmonds and Rafal Maszkowski 14 Dec 1992 // // This program is licensed under the GNU Library General Public License, v2 // // Copyright 2003 Robert Love // Copyright 2004 Albert Cahalan #include "proc/sysinfo.h" #include "proc/version.h" //#include <errno.h> #include <fcntl.h> #include <getopt.h> #include <stdio.h> #include <stdlib.h> ... if(!old_fmt){ unsigned KLONG buffers_plus_cached = kb_main_buffers + kb_main_cached; printf( "-/+ buffers/cache: %10Lu %10Lu\n", S(kb_main_used - buffers_plus_cached), S(kb_main_free + buffers_plus_cached) ); }
お、Google の Robert Love の名前が。
- /usr/local/src/procps-3.2.8/sysinfo.h
38 /* derived values */ 39 extern unsigned long kb_swap_used; 40 extern unsigned long kb_main_used;
- /usr/local/src/procps-3.2.8/proc/sysinfo.c
484 void meminfo(void){ 485 char namebuf[16]; /* big enough to hold any row name */ 486 mem_table_struct findme = { namebuf, NULL}; 487 mem_table_struct *found; 488 char *head; 489 char *tail; 490 static const mem_table_struct mem_table[] = { 491 {"Active", &kb_active}, // important 492 {"AnonPages", &kb_anon_pages}, 493 {"Bounce", &kb_bounce}, 494 {"Buffers", &kb_main_buffers}, // important 495 {"Cached", &kb_main_cached}, // important 496 {"CommitLimit", &kb_commit_limit}, ... 509 {"MemFree", &kb_main_free}, // important 510 {"MemShared", &kb_main_shared}, // important, but now gone! 511 {"MemTotal", &kb_main_total}, // important ... 517 {"Slab", &kb_slab}, // kB version of vmstat nr_slab 518 {"SwapCached", &kb_swap_cached}, 519 {"SwapFree", &kb_swap_free}, // important 520 {"SwapTotal", &kb_swap_total}, // important 521 {"VmallocChunk", &kb_vmalloc_chunk}, 522 {"VmallocTotal", &kb_vmalloc_total}, 523 {"VmallocUsed", &kb_vmalloc_used}, 524 {"Writeback", &kb_writeback}, // kB version of vmstat nr_writeback 525 }; 526 const int mem_table_count = sizeof(mem_table)/sizeof(mem_table_struct); 527 FILE_TO_BUF(MEMINFO_FILE,meminfo_fd); 528 kb_inactive = ~0UL; 529 head = buf; 530 for(;;){ 531 tail = strchr(head, ':'); 532 if(!tail) break; 533 *tail = '\0'; 534 if(strlen(head) >= sizeof(namebuf)){ 535 head = tail+1; 536 goto nextline; 537 } 538 strcpy(namebuf,head); 539 found = bsearch(&findme, mem_table, mem_table_count, 540 sizeof(mem_table_struct), compare_mem_table_structs 541 ); 542 head = tail+1; 543 if(!found) goto nextline; 544 *(found->slot) = strtoul(head,&tail,10); 545 nextline: 546 tail = strchr(head, '\n'); 547 if(!tail) break; 548 head = tail+1; 549 } 550 if(!kb_low_total){ /* low==main except with large-memory support */ 551 kb_low_total = kb_main_total; 552 kb_low_free = kb_main_free; 553 } 554 if(kb_inactive==~0UL){ 555 kb_inactive = kb_inact_dirty + kb_inact_clean + kb_inact_laundry; 556 } 557 kb_swap_used = kb_swap_total - kb_swap_free; 558 kb_main_used = kb_main_total - kb_main_free; 559 }
ということで、
free の used(-/+ buffers/cache): /proc/meminfo の MemTotal - MemFree - (Buffers + Cached)
ということになるようだ。
ここから先は fs/proc/meminfo.c から先を調べればよい。
29 /* 30 * display in kilobytes. 31 */ 32 #define K(x) ((x) << (PAGE_SHIFT - 10)) 33 si_meminfo(&i); 34 si_swapinfo(&i); 35 committed = percpu_counter_read_positive(&vm_committed_as); 36 allowed = ((totalram_pages - hugetlb_total_pages()) 37 * sysctl_overcommit_ratio / 100) + total_swap_pages; 38 cached = global_page_state(NR_FILE_PAGES) - 39 total_swapcache_pages - i.bufferram; 40 if (cached < 0) 41 cached = 0; 42 get_vmalloc_info(&vmi); 43 for (lru = LRU_BASE; lru < NR_LRU_LISTS; lru++) 44 pages[lru] = global_page_state(NR_LRU_BASE + lru); 45 /* 46 * Tagged format, for easy grepping and expansion. 47 */ 48 seq_printf(m, 49 "MemTotal: %8lu kB\n" 50 "MemFree: %8lu kB\n" 51 "Buffers: %8lu kB\n" 52 "Cached: %8lu kB\n" ... 101 K(i.totalram), 102 K(i.freeram), 103 K(i.bufferram), 104 K(cached), 105 K(total_swapcache_pages),
2178 void si_meminfo(struct sysinfo *val) 2179 { 2180 val->totalram = totalram_pages; 2181 val->sharedram = 0; 2182 val->freeram = global_page_state(NR_FREE_PAGES); 2183 val->bufferram = nr_blockdev_pages(); 2184 val->totalhigh = totalhigh_pages; 2185 val->freehigh = nr_free_highpages(); 2186 val->mem_unit = PAGE_SIZE; 2187 }
75 extern atomic_long_t vm_stat[NR_VM_ZONE_STAT_ITEMS]; ... 82 static inline unsigned long global_page_state(enum zone_stat_item item) 83 { 84 long x = atomic_long_read(&vm_stat[item]); 85 #ifdef CONFIG_SMP 86 if (x < 0) 87 x = 0; 88 #endif 89 return x; 90 }
よくわからんが、HugePages はカーネル空間に確保されて、空き領域として扱われないということだろうw
使った環境は以下の通り。
yazekats% cat /etc/issue Oracle Linux Server release 6.4 Kernel \r on an \m yazekats% cat /proc/version Linux version 2.6.39-400.17.1.el6uek.x86_64 (mockbuild@ca-build44.us.oracle.com) (gcc version 4.4.7 20120313 (Red Hat 4.4.7-3) (GCC) ) #1 SMP Fri Feb 22 18:16:18 PST 2013
