FreeBSD 兮 malloc

by thinker

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FreeBSD

為啥麼，明明就是個小程式，結果佔 memory 50MB? 這是懷疑真久兮問題，就像下面兮 code 要用 50MB 兮空間，你敢相信？

{{{
#include <stdio.h>
#include <unistd.h>

main() {
        sleep(10);
}
}}}

實際上，static link 和 dynamic link 兮版本，大小差真多。
{{{
gcc -o sleep_d sleep.c
gcc -o sleep_s -static sleep.c
}}}

下面是 static 版本兮執行結果:
{{{
thinker@fishman$$ ./sleep_s& ps aux|grep sleep_s
[1] 45074
thinker 45074  0.0  0.2 48992   196  p5  S     7:15PM   0:00.02 ./sleep_s
thinker 45076  0.0  0.8 50296   968  p5  S+    7:15PM   0:00.07 grep sleep_s
}}}
VSZ 是 48992KB，而 RSS 是 196k。

這是 dynamic 版本兮執行結果:
{{{
thinker@fishman$$ ./sleep_d& ps aux|grep sleep_d
[1] 45633
thinker 45633  0.0  0.4  1244   460  p5  S     7:16PM   0:00.03 ./sleep_d
thinker 45635  0.0  0.8 50296   932  p5  R+    7:16PM   0:00.06 grep sleep_d
thinker@fishman$$ 
}}}
VSZ 是 1244KB，而 RSS 是 460KB。

但，static 版本敢真正大這麼多？
{{{
thinker@fishman$$ ls -l sleep_[sd]
-rwxr-xr-x  1 thinker  users    4713 Jan 29 19:15 sleep_d
-rwxr-xr-x  1 thinker  users  174226 Jan 29 19:15 sleep_s
thinker@fishman$$ 
}}}
174KB V.S. 4.7KB，是差抹少，但是 170KB 會差這多？48MB 比 1.2MB，不免乎我懷疑。

strip 看麼:
{{{
thinker@fishman$$ strip sleep_[ds]
thinker@fishman$$ ls -l sleep_[sd]
-rwxr-xr-x  1 thinker  users    3012 Jan 29 19:21 sleep_d
-rwxr-xr-x  1 thinker  users  139208 Jan 29 19:21 sleep_s
thinker@fishman$$ 
}}}
也是差無多。

== 執行檔 header ==

用 readelf 檢查 static 執行檔兮內容:
{{{
thinker@fishman$$ readelf -a sleep_s 
ELF Header:
  Magic:   7f 45 4c 46 01 01 01 09 00 00 00 00 00 00 00 00 
  Class:                             ELF32
  Data:                              2's complement, little endian
  Version:                           1 (current)
  OS/ABI:                            UNIX - $FreeBSD$
  ABI Version:                       0
  Type:                              EXEC (Executable file)
  Machine:                           Intel 80386
  Version:                           0x1
  Entry point address:               0x8048088
  Start of program headers:          52 (bytes into file)
  Start of section headers:          138688 (bytes into file)
  Flags:                             0x0
  Size of this header:               52 (bytes)
  Size of program headers:           32 (bytes)
  Number of program headers:         2
  Size of section headers:           40 (bytes)
  Number of section headers:         13
  Section header string table index: 12

Section Headers:
  [Nr] Name              Type            Addr     Off    Size   ES Flg Lk Inf Al
  [ 0]                   NULL            00000000 000000 000000 00      0   0  0
  [ 1] .init             PROGBITS        08048074 000074 000011 00  AX  0   0  4
  [ 2] .text             PROGBITS        08048088 000088 0195b7 00  AX  0   0  4
  [ 3] .fini             PROGBITS        08061640 019640 00000c 00  AX  0   0  4
  [ 4] .rodata           PROGBITS        08061660 019660 00385e 00   A  0   0 32
  [ 5] .data             PROGBITS        08065000 01d000 001cc4 00  WA  0   0 32
  [ 6] .eh_frame         PROGBITS        08066cc4 01ecc4 000004 00   A  0   0  4
  [ 7] .ctors            PROGBITS        08066cc8 01ecc8 000008 00  WA  0   0  4
  [ 8] .dtors            PROGBITS        08066cd0 01ecd0 000008 00  WA  0   0  4
  [ 9] .jcr              PROGBITS        08066cd8 01ecd8 000004 00  WA  0   0  4
  [10] .bss              NOBITS          08066ce0 01ece0 003068 00  WA  0   0 32
  [11] .comment          PROGBITS        00000000 01ece0 003087 00      0   0  1
  [12] .shstrtab         STRTAB          00000000 021d67 000056 00      0   0  1
Key to Flags:
  W (write), A (alloc), X (execute), M (merge), S (strings)
  I (info), L (link order), G (group), x (unknown)
  O (extra OS processing required) o (OS specific), p (processor specific)

Program Headers:
  Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg Align
  LOAD           0x000000 0x08048000 0x08048000 0x1cebe 0x1cebe R E 0x1000
  LOAD           0x01d000 0x08065000 0x08065000 0x01cdc 0x04d48 RW  0x1000

Section to Segment mapping:
  Segment Sections...
   00     .init .text .fini .rodata 
   01     .data .eh_frame .ctors .dtors .jcr .bss

There is no dynamic segment in this file.

There are no relocations in this file.

There are no unwind sections in this file.

No version information found in this file.
thinker@fishman$$ 
}}}
readelf 顯示，loader 會對執行檔 load 兩個 segement，第一個兮 memory size 是 0x1cebe，第二個是 0x04d48。也就是 138246 bytes 左右 => 138KB。也就是，多出 4XMB 是 heap 和 stack？但是 dynamic 版本沒用這麼多 heap 和 stack？heap 兮配置，應該和 libc 兮記憶體管理有關係，所以我查了 malloc(3) 之後，發現可以在程式結果時，印出配置狀況。

== MALLOC 兮$統計$資料 ==

{{{
thinker@fishman$$ MALLOC_OPTIONS=P ./sleep_s 2>&1|more
___ Begin malloc statistics ___
Number of CPUs: 1
Number of arenas: 1
Cache slots: 256
Chunk size: 16777216 (2^24)
Quantum size: 16 (2^4)
Pointer size: 4
Number of bins: 128
Maximum bin size: 2096
Assertions enabled
Redzone size: 16
Allocated: 128, space used: 33554432

chunks:
       nchunks   highchunks    curchunks
             2            2            2

arenas[0] statistics:
calls:
       nmalloc      npalloc      ncalloc      ndalloc      nralloc
             2            0            0            0            0
region events:
        nsplit    ncoalesce
...... SKIP .......
}}}
哇 33554432 bytes == 33.5MB !!! 怎麼一次就配這麼多?

再看看 dynamic 版本，配比較少 heap?
{{{
thinker@fishman$$ MALLOC_OPTIONS=P ./sleep_d 2>&1|more
thinker@fishman$$ 
}}}
咧!! 無配?? 無可能，敢是因為沒使用到 heap，所以無配？但是，為什麼 static 版本就先配好？敢說 static 和 dynamic 兮 initial code 作沒無同？

來試看昧:
{{{
#include <stdio.h>
#include <unistd.h>

main() {
        char *p; 
        
        p = (char *)malloc(16);
        sleep(10);
}
}}}
執行 malloc 之後，應該都會配置。

compile:
{{{
thinker@fishman$$ gcc -o sleep_s -static sleep.c
thinker@fishman$$ gcc -o sleep_d sleep.c
thinker@fishman$$ ls -l sleep_[sd]
-rwxr-xr-x  1 thinker  users    4808 Jan 29 19:44 sleep_d
-rwxr-xr-x  1 thinker  users  174226 Jan 29 19:44 sleep_s
thinker@fishman$$ 
}}}
看起來，大小差無多。

{{{
thinker@fishman$$ ./sleep_d& ps aux|grep sleep_d
[1] 60455
thinker 60455  0.0  0.5 50100   632  p5  S     7:47PM   0:00.04 ./sleep_d
thinker 60457  0.0  0.8 50296   964  p5  R+    7:47PM   0:00.08 grep sleep_d
thinker@fishman$$

thinker@fishman$$ ./sleep_s& ps aux|grep sleep_s
[1] 61199
thinker 61199  0.0  0.2 48992   196  p5  S     7:48PM   0:00.02 ./sleep_s
thinker 61201  0.0  0.8 50296   964  p5  S+    7:48PM   0:00.06 grep sleep_s
thinker@fishman$$ 
}}}
哈!大小差不多。所以，應該是兩個版本兮 initial code 兮處理方法無同。

來看看 malloc 兮配置:
{{{
thinker@fishman$$ MALLOC_OPTIONS=P ./sleep_d 2>&1|more
___ Begin malloc statistics ___
Number of CPUs: 1
Number of arenas: 1
Cache slots: 256
Chunk size: 16777216 (2^24)
Quantum size: 16 (2^4)
Pointer size: 4
Number of bins: 128
Maximum bin size: 2096
Assertions enabled
Redzone size: 16
Allocated: 64, space used: 33554432

chunks:
       nchunks   highchunks    curchunks
             2            2            2

arenas[0] statistics:
calls:
       nmalloc      npalloc      ncalloc      ndalloc      nralloc
             1            0            0            0            0
region events:
        nsplit    ncoalesce
...... SKIP ......
}}}
嘿! malloc 有進行記憶體兮配置。

== 結論 ==
malloc 一開始就會配 3xMB 左右兮空間，看起真浪費。但是，另一方面，配置之後若是無用著，只是在 page table 佔一點空間而己，並抹實際配得 memory，連 swap 也抹用著。這是為啥麼，咱常常會懷疑，明明是 hello world 兮小程式，卻用這麼多兮空間。如果你注意看 bash:
{{{
thinker@fishman$$ ps aux|grep bash
root      462  0.0  0.0  3180     0  v0  IW   -         0:00.00 -bash (bash)
thinker 45922  0.0  0.3  3156   372  p1  Is    3:02PM   0:00.56 bash
thinker 64172  0.0  0.3  3152   364  p2  Is    3:29PM   0:00.27 bash
thinker 65191  0.0  0.8 50296   964  p5  S+    7:53PM   0:00.06 grep bash
thinker@fishman$$ 
}}}
皆比咱兮  hello world 小，這是啥情形？？!! 其實就是 heap 兮問題。這類程式，應該在 heap 兮使用上，有特別兮設計。甚至是無用 $FreeBSD$ 兮 malloc，而是用自己兮版本。下一次，在算記憶體用量兮時，應該也將配了，卻無佇用兮空間可慮入去。

== $FreeBSD$ 版本 ==
{{{
thinker@fishman$$ uname -a
$FreeBSD$ fishman.branda.to 7.0-CURRENT $FreeBSD$ 7.0-CURRENT #0: Sat Jan 28 18:12:49 CST 2006
     thinker@fishman.branda.to:/usr/obj/usr/src/sys/GENERIC  i386
thinker@fishman$$ 
}}}

最後更新時間: 2006-01-29 21:16:37 CST | 引用

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