On 01/29/2016 02:45 AM, Pavel Machek wrote:
Hi!
By default, page poisoning uses a poison value (0xaa) on free. If this
is changed to 0, the page is not only sanitized but zeroing on alloc
with __GFP_ZERO can be skipped as well. The tradeoff is that detecting
corruption from the poisoning is harder to detect. This feature also
cannot be used with hibernation since pages are not guaranteed to be
zeroed after hibernation.
So... this makes kernel harder to debug for performance advantage...?
If so.. how big is the performance advantage?
Pavel
The performance advantage really depends on the benchmark you are running.
It was pointed out this may help some unknown amount with merging pages
in VMs since the pages are now identical and can be merged. The debugging
is also only slightly more difficult. With the non-zero poisoning value
it's easier to see that a crash was caused by triggering the poison vs.
just some random NULL pointer.
As as been pointed out, this help text could use some updating so I'll
clarify this more.
Thanks,
Laura
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