On Tue, 20 Dec 2011 19:25:04 -0800 (PST) Hugh Dickins <hughd@xxxxxxxxxx> wrote: > On Wed, 21 Dec 2011, KAMEZAWA Hiroyuki wrote: > > On Tue, 20 Dec 2011 09:24:47 +0900 > > Hiroyuki Kamezawa <kamezawa.hiroyuki@xxxxxxxxx> wrote: > > > 2011/12/20 Hugh Dickins <hughd@xxxxxxxxxx>: > > > > > > > I speak from experience: I did *exactly* the same at "bypass" when > > > > I introduced our mem_cgroup_reset_page(), which corresponds to your > > > > mem_cgroup_reset_owner(); it seemed right to me that a successful > > > > (return 0) call to try_charge() should provide a good *ptr. > > > > > > > ok. > > > > > > > But others (Ying and Greg) pointed out that it changes the semantics > > > > of __mem_cgroup_try_charge() in this case, so you need to justify the > > > > change to all those places which do something like "if (ret || !memcg)" > > > > after calling it. Perhaps it is a good change everywhere, but that's > > > > not obvious, so we chose caution. > > > > > > > > Doesn't it lead to bypass pages being marked as charged to root, so > > > > they don't get charged to the right owner next time they're touched? > > > > > > > Yes. You're right. > > > Hm. So, it seems I should add reset_owner() to the !memcg path > > > rather than here. > > > > > Considering this again.. > > > > Now, we catch 'charge' event only once in lifetime of anon/file page. > > So, it doesn't depend on that it's marked as PCG_USED or not. > > That's an interesting argument, I hadn't been looking at it that way. > It's not true of swapcache, but I guess we don't need to preserve its > peculiarities in this case. > > I've not checked the (ret || !memcg) cases yet to see if any change > needed there. > > I certainly like that the success return guarantees that memcg is set. > Hmm. Ok, then....I'll update patch description to be precise. And check I can remove !memcg case in the same patch. Then, repost v2. Thanks, -Kame -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
