(2012/04/20 15:39), Ying Han wrote: > On Thu, Apr 19, 2012 at 11:16 PM, KAMEZAWA Hiroyuki > <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote: >> (2012/04/20 14:57), Ying Han wrote: >> >>> On Thu, Apr 19, 2012 at 5:37 PM, KAMEZAWA Hiroyuki >>> <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote: >>>> (2012/04/19 22:12), Johannes Weiner wrote: >>>>> Plus this code runs for ALL uncharges, the unlikely() and preliminary >>>>> flag testing don't make it okay. It's bad that we have this in the >>>>> allocator, but at least it would be good to hook into that branch and >>>>> not add another one. >>>>> >>>>> pc->mem_cgroup stays intact after the uncharge. Could we make the >>>>> memcg removal path wait on the mlock counter to drop to zero instead >>>>> and otherwise keep Ying's version? >>>>> >>>> >>>> >>>> handling problem in ->destroy() path ? Hmm, it will work against use-after-free. >>> >>>> But accounting problem which may be caused by mem_cgroup_lru_add_list() cannot >>>> be handled, which overwrites pc->mem_cgroup. >>> >>> Kame, can you clarify that? What the mem_cgroup_lru_add_list() has >>> anything to do w/ this problem? >>> >> >> >> It overwrites pc->mem_cgroup. Then, Assume a task in cgroup "A". >> >> 1. page is charged. pc->mem_cgroup = A + Used bit. >> 2. page is set Mlocked. A's mlock-counter += 1 >> 3. page is uncharged - Used bit. >> 4. page is added to lru pc->mem_cgroup = root >> 5. page is freed root's mlock-coutner -=1, >> >> Then, A's mlock-counter +1, root's mlock-counter -1 IF free_pages() >> really handle mlocked pages... > > Hmm, now the question is whether the TestClearPageMlock() should only > happen between step 2 and step 3. If so, the mlock stat will be > updated correctly. > Yes, I think it's true. TestClearPageMlock() should happen betwen 2 and 3, I believe. >> Sigh...."This shouldn't happen"!!!!! >> >> How about adding warning to free_page() path and remove your current hook ? > > That does make thing a lot simpler.. I will wait a bit in case someone > remember a counter example? > Sure. Thank you for your works. Thanks, -Kame -- 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>