| Message ID | 0773058df022fa701b78f9a6dfe3c501a1a77351.1705928395.git.baolin.wang@linux.alibaba.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [1/2] mm: compaction: limit the suitable target page order to be less than cc->order | expand |
On Mon, Jan 22, 2024 at 09:01:54PM +0800, Baolin Wang wrote: > Currently we will use 'cc->nr_freepages >= cc->nr_migratepages' comparison > to ensure that enough freepages are isolated in isolate_freepages(), however > it just decreases the cc->nr_freepages without updating cc->nr_migratepages > in compaction_alloc(), which will waste more CPU cycles and cause too many > freepages to be isolated. > > So we should also update the cc->nr_migratepages when allocating or freeing > the freepages to avoid isolating excess freepages. And I can see fewer free > pages are scanned and isolated when running thpcompact on my Arm64 server: > k6.7 k6.7_patched > Ops Compaction pages isolated 120692036.00 118160797.00 > Ops Compaction migrate scanned 131210329.00 154093268.00 > Ops Compaction free scanned 1090587971.00 1080632536.00 > Ops Compact scan efficiency 12.03 14.26 > > Moreover, I did not see an obvious latency improvements, this is likely because > isolating freepages is not the bottleneck in the thpcompact test case. > k6.7 k6.7_patched > Amean fault-both-1 1089.76 ( 0.00%) 1080.16 * 0.88%* > Amean fault-both-3 1616.48 ( 0.00%) 1636.65 * -1.25%* > Amean fault-both-5 2266.66 ( 0.00%) 2219.20 * 2.09%* > Amean fault-both-7 2909.84 ( 0.00%) 2801.90 * 3.71%* > Amean fault-both-12 4861.26 ( 0.00%) 4733.25 * 2.63%* > Amean fault-both-18 7351.11 ( 0.00%) 6950.51 * 5.45%* > Amean fault-both-24 9059.30 ( 0.00%) 9159.99 * -1.11%* > Amean fault-both-30 10685.68 ( 0.00%) 11399.02 * -6.68%* > > Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com> Acked-by: Mel Gorman <mgorman@techsingularity.net>
On 1/22/24 14:01, Baolin Wang wrote: > Currently we will use 'cc->nr_freepages >= cc->nr_migratepages' comparison > to ensure that enough freepages are isolated in isolate_freepages(), however > it just decreases the cc->nr_freepages without updating cc->nr_migratepages > in compaction_alloc(), which will waste more CPU cycles and cause too many > freepages to be isolated. Hm yeah I guess this can happen with fast_isolate_freepages() if it returns with something but not all the freepages that are expected to be needed, and then we get to isolate_freepages() again. > So we should also update the cc->nr_migratepages when allocating or freeing > the freepages to avoid isolating excess freepages. And I can see fewer free > pages are scanned and isolated when running thpcompact on my Arm64 server: > k6.7 k6.7_patched > Ops Compaction pages isolated 120692036.00 118160797.00 > Ops Compaction migrate scanned 131210329.00 154093268.00 > Ops Compaction free scanned 1090587971.00 1080632536.00 > Ops Compact scan efficiency 12.03 14.26 > > Moreover, I did not see an obvious latency improvements, this is likely because > isolating freepages is not the bottleneck in the thpcompact test case. > k6.7 k6.7_patched > Amean fault-both-1 1089.76 ( 0.00%) 1080.16 * 0.88%* > Amean fault-both-3 1616.48 ( 0.00%) 1636.65 * -1.25%* > Amean fault-both-5 2266.66 ( 0.00%) 2219.20 * 2.09%* > Amean fault-both-7 2909.84 ( 0.00%) 2801.90 * 3.71%* > Amean fault-both-12 4861.26 ( 0.00%) 4733.25 * 2.63%* > Amean fault-both-18 7351.11 ( 0.00%) 6950.51 * 5.45%* > Amean fault-both-24 9059.30 ( 0.00%) 9159.99 * -1.11%* > Amean fault-both-30 10685.68 ( 0.00%) 11399.02 * -6.68%* > > Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com> > --- > mm/compaction.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/mm/compaction.c b/mm/compaction.c > index 066b72b3471a..6c84e3a5b32b 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -1779,6 +1779,7 @@ static struct folio *compaction_alloc(struct folio *src, unsigned long data) > dst = list_entry(cc->freepages.next, struct folio, lru); > list_del(&dst->lru); > cc->nr_freepages--; > + cc->nr_migratepages--; This is breaking the tracepoint TRACE_EVENT(mm_compaction_migratepages) which does __entry->nr_failed = cc->nr_migratepages - nr_succeeded; and is called after migrate_pages() finishes, so now this will underflow. Probably need to get a snapshot of cc->nr_migratepages before calling migrate_pages() and then feed that to the tracepoint instead of cc. > > return dst; > } > @@ -1794,6 +1795,7 @@ static void compaction_free(struct folio *dst, unsigned long data) > > list_add(&dst->lru, &cc->freepages); > cc->nr_freepages++; > + cc->nr_migratepages++; > } > > /* possible outcome of isolate_migratepages */
On 2024/2/12 18:32, Vlastimil Babka wrote: > On 1/22/24 14:01, Baolin Wang wrote: >> Currently we will use 'cc->nr_freepages >= cc->nr_migratepages' comparison >> to ensure that enough freepages are isolated in isolate_freepages(), however >> it just decreases the cc->nr_freepages without updating cc->nr_migratepages >> in compaction_alloc(), which will waste more CPU cycles and cause too many >> freepages to be isolated. > > Hm yeah I guess this can happen with fast_isolate_freepages() if it returns > with something but not all the freepages that are expected to be needed, and > then we get to isolate_freepages() again. Yes. > >> So we should also update the cc->nr_migratepages when allocating or freeing >> the freepages to avoid isolating excess freepages. And I can see fewer free >> pages are scanned and isolated when running thpcompact on my Arm64 server: >> k6.7 k6.7_patched >> Ops Compaction pages isolated 120692036.00 118160797.00 >> Ops Compaction migrate scanned 131210329.00 154093268.00 >> Ops Compaction free scanned 1090587971.00 1080632536.00 >> Ops Compact scan efficiency 12.03 14.26 >> >> Moreover, I did not see an obvious latency improvements, this is likely because >> isolating freepages is not the bottleneck in the thpcompact test case. >> k6.7 k6.7_patched >> Amean fault-both-1 1089.76 ( 0.00%) 1080.16 * 0.88%* >> Amean fault-both-3 1616.48 ( 0.00%) 1636.65 * -1.25%* >> Amean fault-both-5 2266.66 ( 0.00%) 2219.20 * 2.09%* >> Amean fault-both-7 2909.84 ( 0.00%) 2801.90 * 3.71%* >> Amean fault-both-12 4861.26 ( 0.00%) 4733.25 * 2.63%* >> Amean fault-both-18 7351.11 ( 0.00%) 6950.51 * 5.45%* >> Amean fault-both-24 9059.30 ( 0.00%) 9159.99 * -1.11%* >> Amean fault-both-30 10685.68 ( 0.00%) 11399.02 * -6.68%* >> >> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com> >> --- >> mm/compaction.c | 2 ++ >> 1 file changed, 2 insertions(+) >> >> diff --git a/mm/compaction.c b/mm/compaction.c >> index 066b72b3471a..6c84e3a5b32b 100644 >> --- a/mm/compaction.c >> +++ b/mm/compaction.c >> @@ -1779,6 +1779,7 @@ static struct folio *compaction_alloc(struct folio *src, unsigned long data) >> dst = list_entry(cc->freepages.next, struct folio, lru); >> list_del(&dst->lru); >> cc->nr_freepages--; >> + cc->nr_migratepages--; > > This is breaking the tracepoint TRACE_EVENT(mm_compaction_migratepages) > which does > > __entry->nr_failed = cc->nr_migratepages - nr_succeeded; > > and is called after migrate_pages() finishes, so now this will underflow. > > Probably need to get a snapshot of cc->nr_migratepages before calling > migrate_pages() and then feed that to the tracepoint instead of cc. Ah, good catch. Will fix in next version. Thanks.
diff --git a/mm/compaction.c b/mm/compaction.c index 066b72b3471a..6c84e3a5b32b 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -1779,6 +1779,7 @@ static struct folio *compaction_alloc(struct folio *src, unsigned long data) dst = list_entry(cc->freepages.next, struct folio, lru); list_del(&dst->lru); cc->nr_freepages--; + cc->nr_migratepages--; return dst; } @@ -1794,6 +1795,7 @@ static void compaction_free(struct folio *dst, unsigned long data) list_add(&dst->lru, &cc->freepages); cc->nr_freepages++; + cc->nr_migratepages++; } /* possible outcome of isolate_migratepages */
Currently we will use 'cc->nr_freepages >= cc->nr_migratepages' comparison to ensure that enough freepages are isolated in isolate_freepages(), however it just decreases the cc->nr_freepages without updating cc->nr_migratepages in compaction_alloc(), which will waste more CPU cycles and cause too many freepages to be isolated. So we should also update the cc->nr_migratepages when allocating or freeing the freepages to avoid isolating excess freepages. And I can see fewer free pages are scanned and isolated when running thpcompact on my Arm64 server: k6.7 k6.7_patched Ops Compaction pages isolated 120692036.00 118160797.00 Ops Compaction migrate scanned 131210329.00 154093268.00 Ops Compaction free scanned 1090587971.00 1080632536.00 Ops Compact scan efficiency 12.03 14.26 Moreover, I did not see an obvious latency improvements, this is likely because isolating freepages is not the bottleneck in the thpcompact test case. k6.7 k6.7_patched Amean fault-both-1 1089.76 ( 0.00%) 1080.16 * 0.88%* Amean fault-both-3 1616.48 ( 0.00%) 1636.65 * -1.25%* Amean fault-both-5 2266.66 ( 0.00%) 2219.20 * 2.09%* Amean fault-both-7 2909.84 ( 0.00%) 2801.90 * 3.71%* Amean fault-both-12 4861.26 ( 0.00%) 4733.25 * 2.63%* Amean fault-both-18 7351.11 ( 0.00%) 6950.51 * 5.45%* Amean fault-both-24 9059.30 ( 0.00%) 9159.99 * -1.11%* Amean fault-both-30 10685.68 ( 0.00%) 11399.02 * -6.68%* Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com> --- mm/compaction.c | 2 ++ 1 file changed, 2 insertions(+)