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 <handai....@taobao.com> > > > > 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. [...] -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
