Messages in this thread | | | Date | Mon, 18 Jan 2010 11:10:56 +0900 | Subject | Re: [PATCH 2/3][v2] vmstat: add anon_scan_ratio field to zoneinfo | From | Minchan Kim <> |
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I missed Cc.
On Mon, Jan 18, 2010 at 10:54 AM, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote: >> Hi, KOSAKI. >> >> On Mon, Jan 18, 2010 at 10:04 AM, KOSAKI Motohiro >> <kosaki.motohiro@jp.fujitsu.com> wrote: >> >> Hi, KOSAKI. >> >> >> >> On Thu, Jan 14, 2010 at 2:18 PM, KOSAKI Motohiro >> >> <kosaki.motohiro@jp.fujitsu.com> wrote: >> >> >> > Well. zone->lock and zone->lru_lock should be not taked at the same time. >> >> >> >> >> >> I looked over the code since I am out of office. >> >> >> I can't find any locking problem zone->lock and zone->lru_lock. >> >> >> Do you know any locking order problem? >> >> >> Could you explain it with call graph if you don't mind? >> >> >> >> >> >> I am out of office by tomorrow so I can't reply quickly. >> >> >> Sorry for late reponse. >> >> > >> >> > This is not lock order issue. both zone->lock and zone->lru_lock are >> >> > hotpath lock. then, same tame grabbing might cause performance impact. >> >> >> >> Sorry for late response. >> >> >> >> Your patch makes get_anon_scan_ratio of zoneinfo stale. >> >> What you said about performance impact is effective when VM pressure high. >> >> I think stale data is all right normally. >> >> But when VM pressure is high and we want to see the information in zoneinfo( >> >> this case is what you said), stale data is not a good, I think. >> >> >> >> If it's not a strong argue, I want to use old get_scan_ratio >> >> in get_anon_scan_ratio. >> > >> > please looks such function again. >> > >> > usally we use recent_rotated/recent_scanned ratio. then following >> > decreasing doesn't change any scan-ratio meaning. it only prevent >> > stat overflow. >> >> It has a primary role that floating average as well as prevenitng overflow. :) >> So, It's important. >> >> > >> > if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) { >> > spin_lock_irq(&zone->lru_lock); >> > reclaim_stat->recent_scanned[0] /= 2; >> > reclaim_stat->recent_rotated[0] /= 2; >> > spin_unlock_irq(&zone->lru_lock); >> > } >> > >> > >> > So, I don't think current implementation can show stale data. >> >> It can make stale data when high memory pressure happens. > > ?? why? and when? > I think it depend on what's stale mean. > > Currently(i.e. before the patch), get_scan_ratio have following fomula. > in such region, recent_scanned is not protected by zone->lru_lock. > > ap = (anon_prio + 1) * (reclaim_stat->recent_scanned[0] + 1); > ap /= reclaim_stat->recent_rotated[0] + 1; > fp = (file_prio + 1) * (reclaim_stat->recent_scanned[1] + 1); > fp /= reclaim_stat->recent_rotated[1] + 1; > percent[0] = 100 * ap / (ap + fp + 1); > percent[1] = 100 - percent[0]; > > It mean, shrink_zone() doesn't use exactly recent_scanned value. then > zoneinfo can use the same unexactly value.
Absoultely right. I missed that. Thanks. get_scan_ratio used lru_lock to get reclaim_stat->recent_xxxx. But, it doesn't used lru_lock to get ap/fp.
Is it intentional? I think you or Rik know it. :) I think if we want to get exact value, we have to use lru_lock until getting ap/fp. If it isn't, we don't need lru_lock when we get the reclaim_stat->recent_xxxx.
What do you think about it?
> > >> Moreever, I don't want to make complicate thing(ie, need_update) >> than old if it doesn't have some benefit.(I think lru_lock isn't big overhead) > > Hmm.. > I think lru_lock can makes big overhead.
I don't want to argue strongly about this. That's because i don't have seen that. If you have a conern about lru_lock, I don't opposed your patch.
-- Kind regards, Minchan Kim -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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