A few years ago, Davide posted patches to address clear_page() showing
up high in the kernel profiles.
http://thread.gmane.org/gmane.linux.kernel/548928
With malloc implementations that try to conserve the RSS by madvising
away unused pages that are dirty (i.e. faulted in), we pay a high cost
in clear_page() if that page is needed later by the same process.
Now that we have memcgs with their own LRU lists, I was thinking of a
MAP_NOZERO implementation that tries to avoid zero'ing the page if it's
coming from the same memcg.
This will probably need an extra PCG_* flag maintaining state about
whether the page was moved between memcgs since last use.
Security implications: this is not as good as the UID based checks in
Davide's implementation, so should probably be an opt-in instead of
being enabled by default.
Comments?
-Arun
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