Transparent Huge Pages

Jakob Blomer jakob.blomer at
Mon Feb 20 09:00:19 PST 2012

> If you mmap a huge page (say, 1MB), then MADV_DONTNEED a few 4-KB
> chunks inside, transparent huge pages should break up the huge page so
> it can decommit the parts I asked it to decommit.  If it doesn't, that
> sounds like a kernel bug to me!
> Similarly, if I mmap 1MB, get a huge page, and then touch only a few
> bytes in the middle, the kernel shouldn't commit a huge page.
> If huge pages is behaving how I expect, I don't see why it would cause
> your application to use more memory.
> Just to check, you're measuring RSS, not vsize, right?
It is VmRSS from /proc/$pid/status.  And I find the difference between 
loaded and not loaded in AnonHugePages from /proc/meminfo.

Hm... it's not a vanilla kernel but Scientific Linux 6.2 / Fedora 16.  I 
can check again using a vanilla kernel.


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