CODEWITHSUNDEEP
linuxmemory-managementmalloc
einpoklum
einpoklum

Reputation: 131646

64-bit-capable alternative to mallinfo?

On Linux, we have this (GNU C library) function named mallinfo() which gives you some numbers relating to memory allocation:

struct mallinfo {
       int arena;     /* Non-mmapped space allocated (bytes) */
       int ordblks;   /* Number of free chunks */
       int smblks;    /* Number of free fastbin blocks */
       int hblks;     /* Number of mmapped regions */
       int hblkhd;    /* Space allocated in mmapped regions (bytes) */
       int usmblks;   /* Maximum total allocated space (bytes) */
       int fsmblks;   /* Space in freed fastbin blocks (bytes) */
       int uordblks;  /* Total allocated space (bytes) */
       int fordblks;  /* Total free space (bytes) */
       int keepcost;  /* Top-most, releasable space (bytes) */
};

Strangely enough, those values are typically 32-bit integers (!); well, that really won't do, especially for the values given in number of bytes (e.g. fordblks).

I would guess this is deprecated somehow, and that some other facility is available to get the same information. What is it that alternative facility?

Upvotes: 10

Views: 1715

Answers (2)

LustreOne
LustreOne

Reputation: 349

In glibc 2.33 and later there is a mallinfo2() function that has 64-bit field sizes:

https://sourceware.org/git/?p=glibc.git;a=commit;h=e3960d1c57e57f33e0e846d615788f4ede73b945

/* SVID2/XPG mallinfo2 structure which can handle allocations
   bigger than 4GB.  */

struct mallinfo2
{
  size_t arena;    /* non-mmapped space allocated from system */
  size_t ordblks;  /* number of free chunks */
  size_t smblks;   /* number of fastbin blocks */
  size_t hblks;    /* number of mmapped regions */
  size_t hblkhd;   /* space in mmapped regions */
  size_t usmblks;  /* always 0, preserved for backwards compatibility */
  size_t fsmblks;  /* space available in freed fastbin blocks */
  size_t uordblks; /* total allocated space */
  size_t fordblks; /* total free space */
  size_t keepcost; /* top-most, releasable (via malloc_trim) space */
};

Fixed only 15 years after being reported to glibc maintainers, but better late than never.

Upvotes: 1

KamilCuk
KamilCuk

Reputation: 141155

Use malloc_info(). You need to parse it's xml output.
From the malloc_info man page:

The malloc_info() function is designed to address deficiencies in malloc_stats(3) and mallinfo(3).

Source code for malloc_info is e.g. available here. All variables are stored using size_t and printed out accordingly, it should work on any-bit machines.

E.g. on my system (glibc version 2.26) malloc_info(0, stdout) prints out the following:

<malloc version="1">
<heap nr="0">
<sizes>
</sizes>
<total type="fast" count="0" size="0"/>
<total type="rest" count="0" size="0"/>
<system type="current" size="135168"/>
<system type="max" size="135168"/>
<aspace type="total" size="135168"/>
<aspace type="mprotect" size="135168"/>
</heap>
<total type="fast" count="0" size="0"/>
<total type="rest" count="0" size="0"/>
<total type="mmap" count="0" size="0"/>
<system type="current" size="135168"/>
<system type="max" size="135168"/>
<aspace type="total" size="135168"/>
<aspace type="mprotect" size="135168"/>
</malloc>

Upvotes: 2

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