On Tue, Jan 17, 2012 at 05:39:32PM +0900, KAMEZAWA Hiroyuki wrote:
> On Tue, 17 Jan 2012 17:13:57 +0900
> Minchan Kim <minchan@xxxxxxxxxx> wrote:
>
> > This patch insert memory pressure notify point into vmscan.c
> > Most problem in system slowness is swap-in. swap-in is a synchronous
> > opeartion so that it affects heavily system response.
> >
> > This patch alert it when reclaimer start to reclaim inactive anon list.
> > It seems rather earlier but not bad than too late.
> >
> > Other alert point is when there is few cache pages
> > In this implementation, if it is (cache < free pages),
> > memory pressure notify happens. It has to need more testing and tuning
> > or other hueristic. Any suggesion are welcome.
> >
> > Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
>
> In my 1st impression, isn't this too simple ?
I agree It's too simple. It would be good start point rather than
unnecessary complicated things.
>
>
> > ---
> > mm/vmscan.c | 28 ++++++++++++++++++++++++++++
> > 1 files changed, 28 insertions(+), 0 deletions(-)
> >
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index 2880396..cfa2e2d 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -43,6 +43,7 @@
> > #include <linux/sysctl.h>
> > #include <linux/oom.h>
> > #include <linux/prefetch.h>
> > +#include <linux/low_mem_notify.h>
> >
> > #include <asm/tlbflush.h>
> > #include <asm/div64.h>
> > @@ -2082,16 +2083,43 @@ static void shrink_mem_cgroup_zone(int priority, struct mem_cgroup_zone *mz,
> > {
> > unsigned long nr[NR_LRU_LISTS];
> > unsigned long nr_to_scan;
> > +
> > enum lru_list lru;
> > unsigned long nr_reclaimed, nr_scanned;
> > unsigned long nr_to_reclaim = sc->nr_to_reclaim;
> > struct blk_plug plug;
> > +#ifdef CONFIG_LOW_MEM_NOTIFY
> > + bool low_mem = false;
> > + unsigned long free, file;
> > +#endif
> >
> > restart:
> > nr_reclaimed = 0;
> > nr_scanned = sc->nr_scanned;
> > get_scan_count(mz, sc, nr, priority);
> > +#ifdef CONFIG_LOW_MEM_NOTIFY
> > + /* We want to avoid swapout */
> > + if (nr[LRU_INACTIVE_ANON])
> > + low_mem = true;
>
> IIUC, nr[LRU_INACTIVE_ANON] can be easily > 0.
Yes. But I thought it would be better than late notification.
Late notification ends up swap out which is a big concern about this patch.
More proper timing suggestion helps me a lot.
> And get_scan_count() now check per-memcg-lru. So, this only works when
> memcg is not used.
Hmm, I didn't look at recent memcg/global reclaim unify patch of Johannes.
I need time to look at it.
Thanks.
>
>
> > + /*
> > + * We want to avoid dropping page cache excessively
> > + * in no swap system
> > + */
> > + if (nr_swap_pages <= 0) {
> > + free = zone_page_state(mz->zone, NR_FREE_PAGES);
> > + file = zone_page_state(mz->zone, NR_ACTIVE_FILE) +
> > + zone_page_state(mz->zone, NR_INACTIVE_FILE);
> > + /*
> > + * If we have very few page cache pages,
> > + * notify to user
> > + */
> > + if (file < free)
> > + low_mem = true;
> > + }
>
> I can't understand why you think you can check lowmem condition by "file < free".
The reason I thought so is I want to maintain some page cache to some degree.
But I admit It's very naive heuristic and should be improved.
> And I don't think using per-zone data is good.
> (I'm not sure how many zones embeded guys using..)
Agree. In case of swapless system, we need another heuristic.
>
> Another idea:
> 1. can't we use some technique like cleancache to detect the condition ?
I totally forgot cleancache approach. Could you remind that?
> 2. can't we measure page-in/page-out distance by recording something ?
I can't understand your point. What's relation does it with swapout prevent?
> 3. NR_ANON + NR_FILE_MAPPED can't mean the amount of core memory if we can
> ignore the data file cache ?
It's good but how do we define some amount?
It's very vague but I guess we can get a good idea from that.
Perhaps, you already has it.
> 4. how about checking kswapd's busy status ?
Could you elaborate on your idea?
Kame, Thanks for reply,
>
>
>
> Thanks,
> -Kame
>
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>