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? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>