关于linux：valgrind、massif、top、pmap的比较

Comparing valgrind, massif, top, and pmap

我正在尝试了解我的应用程序是否泄漏。

在运行我的应用程序时，我会定期运行 pmap 并观察：

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mapped: 488256K writeable/private: 90144K shared: 0K
mapped: 488260K writeable/private: 101912K shared: 0K
mapped: 488256K writeable/private: 102708K shared: 0K
mapped: 488260K writeable/private: 105112K shared: 0K

我运行 top 并观察：

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VIRT RES SHR
488260 17684 3020
488256 20060 3032
488256 22700 3032
488256 26132 3032
488256 28772 3032
488256 31880 3032

"RES"和"可写/私有"的增加让我怀疑存在泄漏。但是，运行 valgrind 我没有检测到任何重大泄漏，并且当我中止执行时，我始终如一
看到大约 20Mb 可达内存：

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==19998==
==19998== HEAP SUMMARY:
==19998== in use at exit: 20,351,513 bytes in 974 blocks
==19998== total heap usage: 329,404 allocs, 328,430 frees, 34,562,346 bytes allocated
==19998==
==19998== LEAK SUMMARY:
==19998== definitely lost: 63 bytes in 4 blocks
==19998== indirectly lost: 0 bytes in 0 blocks
==19998== possibly lost: 4,679 bytes in 76 blocks
==19998== still reachable: 20,346,771 bytes in 894 blocks
==19998== suppressed: 0 bytes in 0 blocks
==19998== Rerun with --leak-check=full to see details of leaked memory
==19998==
==19998== For counts of detected and suppressed errors, rerun with: -v
==19998== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

我运行 valgrind --tool=massif 并且还看到 20Mb flat:

massif

问题：有人能解释一下为什么 valgrind 和 massif 告诉我我的程序一直使用 20Mb 内存，但 top 和 pmap 告诉我使用量在增长吗？