On Fri, May 3, 2013 at 5:11 PM, Michal Hocko <[email protected]> wrote: > On Wed 02-01-13 11:44:21, Michal Hocko wrote: >> On Wed 26-12-12 01:26:07, Sha Zhengju wrote: >> > From: Sha Zhengju <[email protected]> >> > >> > This patch adds memcg routines to count dirty pages, which allows memory >> > controller >> > to maintain an accurate view of the amount of its dirty memory and can >> > provide some >> > info for users while cgroup's direct reclaim is working. >> >> I guess you meant targeted resp. (hard/soft) limit reclaim here, >> right? It is true that this is direct reclaim but it is not clear to me >> why the usefulnes should be limitted to the reclaim for users. I would >> understand this if the users was in fact in-kernel users. >> >> [...] >> > To prevent AB/BA deadlock mentioned by Greg Thelen in previous version >> > (https://lkml.org/lkml/2012/7/30/227), we adjust the lock order: >> > ->private_lock --> mapping->tree_lock --> memcg->move_lock. >> > So we need to make mapping->tree_lock ahead of TestSetPageDirty in >> > __set_page_dirty() >> > and __set_page_dirty_nobuffers(). But in order to avoiding useless >> > spinlock contention, >> > a prepare PageDirty() checking is added. >> >> But there is another AA deadlock here I believe. >> page_remove_rmap >> mem_cgroup_begin_update_page_stat <<< 1 >> set_page_dirty >> __set_page_dirty_buffers >> __set_page_dirty >> mem_cgroup_begin_update_page_stat <<< 2 >> move_lock_mem_cgroup >> spin_lock_irqsave(&memcg->move_lock, *flags); > > JFYI since abf09bed (s390/mm: implement software dirty bits) this is no > longer possible. I haven't checked wheter there are other cases like > this one and it should be better if mem_cgroup_begin_update_page_stat > was recursive safe if that can be done without too many hacks. > I will have a look at this (hopefully) sometimes next week. >
Hi Michal, I'm sorry for not being able to return to this problem immediately after LSF/MM. That is good news. IIRC, it's the only place we have encountered recursive problem in accounting memcg dirty pages. But I'll try to revive my previous work of simplifying mem_cgroup_begin_update_page_stat() lock. I'll back to it in next few days. -- Thanks, Sha -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
