On Thu, 14 Jul 2011, mail@xxxxxxxxxxxx wrote: > I working to remove errors from patch, and I integrated it with current THP > infrastructure a little bit, Great, thank you. > but I want ask if following I do following - > it's about get_page, put_page, get_page_unless_zero, put_page_test_zero. > > I want following logic I think it may be better (in x86): > 1) Each THP page will start with 512 refcount (self + 511 tails) > 2) Each get/put will increment usage count only on this page, same test > variants will do (currently those do not make this, so split is broken) > 3) On compounds put page will call put_page_test_zero, if true, it will do > compound lock, ask again if it has 0, if yes it will decrease refcount of > head, if it will fall to zero compound will be freed (double check lock). > 4) Compound lock is this what caller will need to establish if it needs to > operate on transparent huge page in whole. > > Motivation: > I operate on page cache, many assumptions about concurrent call of > put/get_page are and plain using those causes memory leaks, faults, dangling > pointers, etc when I'm going to split compound page. > > Is this acceptable? Sounds plausible, but I really don't know. I do remember that refcounting compounds by head or by tail always raises questions (and access via get_user_pages() is an easily-overlooked path that needs to be kept in mind). But where THP stands today, and how it needs to be changed for this, I have no idea - whereas Andrea, perhaps, will recognize some of your points above and have a more useful response. It's clear that you have much more of a grip on these details than I have at present, so just be guided by the principle of not slowing down the common paths. Hugh -- 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>