On Tue, Apr 10, 2012 at 8:00 AM, Hillf Danton <dhillf@xxxxxxxxx> wrote: > On Tue, Apr 10, 2012 at 3:42 AM, Ying Han <yinghan@xxxxxxxxxx> wrote: >> This reverts commit c38446cc65e1f2b3eb8630c53943b94c4f65f670. >> >> Before the commit, the code makes senses to me but not after the commit. The >> "nr_reclaimed" is the number of pages reclaimed by scanning through the memcg's >> lru lists. The "nr_to_reclaim" is the target value for the whole function. For >> example, we like to early break the reclaim if reclaimed 32 pages under direct >> reclaim (not DEF_PRIORITY). >> >> After the reverted commit, the target "nr_to_reclaim" is decremented each time >> by "nr_reclaimed" but we still use it to compare the "nr_reclaimed". It just >> doesn't make sense to me... >> > I downloaded mm/vmscan.c from the next tree a couple minutes ago, and > see > .nr_to_reclaim = SWAP_CLUSTER_MAX, > and > nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink); > > in try_to_free_pages(). > > I also see > total_scanned += sc->nr_scanned; > if (sc->nr_reclaimed >= sc->nr_to_reclaim) > goto out; > in do_try_to_free_pages(), > > then would you please say a few words about the sense > of the check of nr_to_reclaim? There are two places where we do early break out in direct reclaim path. 1. For each priority loop after calling shrink_zones(), we check (sc->nr_reclaimed >= sc->nr_to_reclaim) 2. For each memcg reclaim (shrink_mem_cgroup_zone) under shrink_zone(), we check (nr_reclaimed >= nr_to_reclaim) The second one says "if 32 (nr_to_reclaim) pages being reclaimed from this memcg under high priority, break". This check is necessary here to prevent over pressure each memcg under shrink_zone(). Regarding the reverted patch, it tries to convert the "nr_reclaimed" to "total_reclaimed" for outer loop (restart). First of all, it changes the logic by doing less work each time should_continue_reclaim() is true. Second, the fix is simply broken by decrementing nr_to_reclaim each time. --Ying > > >> Signed-off-by: Ying Han <yinghan@xxxxxxxxxx> >> --- >> mm/vmscan.c | 7 +------ >> 1 files changed, 1 insertions(+), 6 deletions(-) >> >> diff --git a/mm/vmscan.c b/mm/vmscan.c >> index 33c332b..1a51868 100644 >> --- a/mm/vmscan.c >> +++ b/mm/vmscan.c >> @@ -2107,12 +2107,7 @@ restart: >> * with multiple processes reclaiming pages, the total >> * freeing target can get unreasonably large. >> */ >> - if (nr_reclaimed >= nr_to_reclaim) >> - nr_to_reclaim = 0; >> - else >> - nr_to_reclaim -= nr_reclaimed; >> - >> - if (!nr_to_reclaim && priority < DEF_PRIORITY) >> + if (nr_reclaimed >= nr_to_reclaim && priority < DEF_PRIORITY) >> break; >> } >> blk_finish_plug(&plug); >> -- >> 1.7.7.3 >> -- 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