On 01/04/2017 04:49 PM, Dave Hansen wrote:
On 01/04/2017 03:44 PM, Rob Gardner wrote:
On 01/04/2017 03:40 PM, Dave Hansen wrote:
On 01/04/2017 03:35 PM, Rob Gardner wrote:
Tags are not cleared at all when memory is freed, but rather, lazily
(and automatically) cleared when memory is allocated.
What does "allocated" mean in this context? Physical or virtual? What
does this do, for instance?
The first time a virtual page is touched by a process after the malloc,
the kernel does clear_user_page() or something similar, which zeroes the
memory. At the same time, the memory tags are cleared.
OK, so the tags can't survive a MADV_FREE. That's definitely something
for apps to understand that use MADV_FREE as a substitute for memset().
It also means that tags can't be set for physically unallocated memory.
Neither of those are deal killers, but it would be nice to document it.
This can go into the adi.txt doc file.
How does this all work with large pages?
It works with large pages the same way as normal sized pages. The TTE
for a large page also will have the mcd bit set in it and tags are set
and referenced the same way.
--
Khalid
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