Messages in this thread | | | Date | Tue, 21 Apr 2009 13:25:51 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] Add file based RSS accounting for memory resource controller (v3) |
| |
On Fri, 17 Apr 2009 19:48:38 +0530 Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
> > ... > > We currently don't track file RSS, the RSS we report is actually anon RSS. > All the file mapped pages, come in through the page cache and get accounted > there. This patch adds support for accounting file RSS pages. It should > > 1. Help improve the metrics reported by the memory resource controller > 2. Will form the basis for a future shared memory accounting heuristic > that has been proposed by Kamezawa. > > Unfortunately, we cannot rename the existing "rss" keyword used in memory.stat > to "anon_rss". We however, add "mapped_file" data and hope to educate the end > user through documentation. > > Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com> > > ... > > @@ -1096,6 +1135,10 @@ static int mem_cgroup_move_account(struct page_cgroup *pc, > struct mem_cgroup_per_zone *from_mz, *to_mz; > int nid, zid; > int ret = -EBUSY; > + struct page *page; > + int cpu; > + struct mem_cgroup_stat *stat; > + struct mem_cgroup_stat_cpu *cpustat; > > VM_BUG_ON(from == to); > VM_BUG_ON(PageLRU(pc->page)); > @@ -1116,6 +1159,23 @@ static int mem_cgroup_move_account(struct page_cgroup *pc, > > res_counter_uncharge(&from->res, PAGE_SIZE); > mem_cgroup_charge_statistics(from, pc, false); > + > + page = pc->page; > + if (page_is_file_cache(page) && page_mapped(page)) { > + cpu = smp_processor_id(); > + /* Update mapped_file data for mem_cgroup "from" */ > + stat = &from->stat; > + cpustat = &stat->cpustat[cpu]; > + __mem_cgroup_stat_add_safe(cpustat, MEM_CGROUP_STAT_MAPPED_FILE, > + -1); > + > + /* Update mapped_file data for mem_cgroup "to" */ > + stat = &to->stat; > + cpustat = &stat->cpustat[cpu]; > + __mem_cgroup_stat_add_safe(cpustat, MEM_CGROUP_STAT_MAPPED_FILE, > + 1); > + }
This function (mem_cgroup_move_account()) does a trylock_page_cgroup() and if that fails it will bale out, and the newly-added code will not be executed.
What are the implications of this? Does the missed accounting later get performed somewhere, or does the error remain in place?
That trylock_page_cgroup() really sucks - trylocks usually do. Could someone please raise a patch which completely documents the reasons for its presence, and for any other uncommented/unobvious trylocks?
Where appropriate, the comment should explain why the trylock isn't simply a bug - why it is safe and correct to omit the operations which we wished to perform.
Thanks.
| |