Hi, 2012-02-29, 09:24 -0600, Christoph Lameter wrote: > On Wed, 29 Feb 2012, Namhyung Kim wrote: > > > Unlike SLAB, SLUB doesn't set PG_slab on tail pages, so if a user would > > call free_pages() incorrectly on a object in a tail page, she will get > > confused with the undefined result. Setting the flag would help her by > > emitting a warning on bad_page() in such a case. > > NAK > > You cannot free a tail page of a compound higher order page independently. > You must free the whole compound. > I meant freeing a *slab object* resides in a compound page using buddy system API (e.g. free_pages). I know it's definitely a programming error. However there's no safety net to protect and/or warn such a misbehavior AFAICS - except for head page which has PG_slab set - when it happened by any chance. Without it, it might be possible to free part of tail pages silently, and cause unexpected not-so-funny results some time later. It should be hard to find out. When I ran such a bad code using SLAB, I was able to be notified immediately. That's why I'd like to add this patch to SLUB too. In addition, it will give more correct value for slab pages when using /proc/kpageflags IMHO. -- Regards, Namhyung Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. 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>