Messages in this thread | | | Date | Tue, 24 May 2011 09:11:14 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [PATCH 6/8] memcg asynchronous memory reclaim interface |
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On Mon, 23 May 2011 16:36:20 -0700 Ying Han <yinghan@google.com> wrote:
> On Fri, May 20, 2011 at 4:56 PM, Hiroyuki Kamezawa > <kamezawa.hiroyuki@gmail.com> wrote: > > 2011/5/21 Andrew Morton <akpm@linux-foundation.org>: > >> On Fri, 20 May 2011 12:46:36 +0900 > >> KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote: > >> > >>> This patch adds a logic to keep usage margin to the limit in asynchronous way. > >>> When the usage over some threshould (determined automatically), asynchronous > >>> memory reclaim runs and shrink memory to limit - MEMCG_ASYNC_STOP_MARGIN. > >>> > >>> By this, there will be no difference in total amount of usage of cpu to > >>> scan the LRU > >> > >> This is not true if "don't writepage at all (revisit this when > >> dirty_ratio comes.)" is true. Skipping over dirty pages can cause > >> larger amounts of CPU consumption. > >> > >>> but we'll have a chance to make use of wait time of applications > >>> for freeing memory. For example, when an application read a file or socket, > >>> to fill the newly alloated memory, it needs wait. Async reclaim can make use > >>> of that time and give a chance to reduce latency by background works. > >>> > >>> This patch only includes required hooks to trigger async reclaim and user interfaces. > >>> Core logics will be in the following patches. > >>> > >>> > >>> ... > >>> > >>> /* > >>> + * For example, with transparent hugepages, memory reclaim scan at hitting > >>> + * limit can very long as to reclaim HPAGE_SIZE of memory. This increases > >>> + * latency of page fault and may cause fallback. At usual page allocation, > >>> + * we'll see some (shorter) latency, too. To reduce latency, it's appreciated > >>> + * to free memory in background to make margin to the limit. This consumes > >>> + * cpu but we'll have a chance to make use of wait time of applications > >>> + * (read disk etc..) by asynchronous reclaim. > >>> + * > >>> + * This async reclaim tries to reclaim HPAGE_SIZE * 2 of pages when margin > >>> + * to the limit is smaller than HPAGE_SIZE * 2. This will be enabled > >>> + * automatically when the limit is set and it's greater than the threshold. > >>> + */ > >>> +#if HPAGE_SIZE != PAGE_SIZE > >>> +#define MEMCG_ASYNC_LIMIT_THRESH (HPAGE_SIZE * 64) > >>> +#define MEMCG_ASYNC_MARGIN (HPAGE_SIZE * 4) > >>> +#else /* make the margin as 4M bytes */ > >>> +#define MEMCG_ASYNC_LIMIT_THRESH (128 * 1024 * 1024) > >>> +#define MEMCG_ASYNC_MARGIN (8 * 1024 * 1024) > >>> +#endif > >> > >> Document them, please. How are they used, what are their units. > >> > > > > will do. > > > > > >>> +static void mem_cgroup_may_async_reclaim(struct mem_cgroup *mem); > >>> + > >>> +/* > >>> * The memory controller data structure. The memory controller controls both > >>> * page cache and RSS per cgroup. We would eventually like to provide > >>> * statistics based on the statistics developed by Rik Van Riel for clock-pro, > >>> @@ -278,6 +303,12 @@ struct mem_cgroup { > >>> */ > >>> unsigned long move_charge_at_immigrate; > >>> /* > >>> + * Checks for async reclaim. > >>> + */ > >>> + unsigned long async_flags; > >>> +#define AUTO_ASYNC_ENABLED (0) > >>> +#define USE_AUTO_ASYNC (1) > >> > >> These are really confusing. I looked at the implementation and at the > >> documentation file and I'm still scratching my head. I can't work out > >> why they exist. With the amount of effort I put into it ;) > >> > >> Also, AUTO_ASYNC_ENABLED and USE_AUTO_ASYNC have practically the same > >> meaning, which doesn't help things. > >> > > Ah, yes it's confusing. > > Sorry I was confused by the memory.async_control interface. I assume > that is the knob to turn on/off the bg reclaim on per-memcg basis. But > when I tried to turn it off, it seems not working well: > > $ cat /proc/7248/cgroup > 3:memory:/A > > $ cat /dev/cgroup/memory/A/memory.async_control > 0 >
If enabled and kworker runs, this shows "3", for now. I'll make this simpler in the next post.
> Then i can see the kworkers start running when the memcg A under > memory pressure. There was no other memcgs configured under root.
What kworkers ? For example, many kworkers runs on ext4? on my host. If kworker/u:x works, it may be for memcg (for my host)
Ok, I'll add statistics in v3.
Thanks, -Kame
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