Messages in this thread | | | Date | Wed, 2 Mar 2011 06:32:03 -0600 (CST) | From | Christoph Lameter <> | Subject | Re: [PATCH 2/4] slub,rcu: don't assume the size of struct rcu_head |
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On Tue, 1 Mar 2011, Hugh Dickins wrote:
> > Struct page may be larger for debugging purposes already because of the > > need for extended spinlock data. > > That was so for a long time, but I stopped it just over a year ago > with commit a70caa8ba48f21f46d3b4e71b6b8d14080bbd57a, stop ptlock > enlarging struct page.
Strange. I just played around with in in January and the page struct size changes when I build kernels with full debugging. I have some cmpxchg_double patches here that depend on certain alignment in the page struct. Debugging causes all that stuff to get out of whack so that I had to do some special patches to make sure fields following the spinlock are properly aligned when the sizes change.
> If a union leads to "random junk" overwriting the page->mapping field > when the page is reused, and that junk could resemble the pointer in > question, then KSM would mistakenly think it still owned the page. > Very remote chance, and maybe it amounts to no more than a leak. But > I'd still prefer we keep page->mapping for pointers (sometimes with > lower bits set as flags).
DESTROY BY RCU uses the lru field which follows the mapping field in page struct. Why would random junk overwrite the mapping field?
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