| Message ID | 20190104125011.16071-18-mgorman@techsingularity.net (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Increase success rates and reduce latency of compaction v2 | expand |
On 1/4/19 1:50 PM, Mel Gorman wrote: > Migrate has separate cached PFNs for ASYNC and SYNC* migration on the > basis that some migrations will fail in ASYNC mode. However, if the cached > PFNs match at the start of scanning and pageblocks are skipped due to > having no isolation candidates, then the sync state does not matter. > This patch keeps matching cached PFNs in sync until a pageblock with > isolation candidates is found. > > The actual benefit is marginal given that the sync scanner following the > async scanner will often skip a number of pageblocks but it's useless > work. Any benefit depends heavily on whether the scanners restarted > recently so overall the reduction in scan rates is a mere 2.8% which > is borderline noise. > > Signed-off-by: Mel Gorman <mgorman@techsingularity.net> Acked-by: Vlastimil Babka <vbabka@suse.cz> My easlier suggestion to check more thoroughly if pages can be migrated (which depends on the mode) before isolating them wouldn't play nice with this :)
On Thu, Jan 17, 2019 at 06:17:28PM +0100, Vlastimil Babka wrote: > On 1/4/19 1:50 PM, Mel Gorman wrote: > > Migrate has separate cached PFNs for ASYNC and SYNC* migration on the > > basis that some migrations will fail in ASYNC mode. However, if the cached > > PFNs match at the start of scanning and pageblocks are skipped due to > > having no isolation candidates, then the sync state does not matter. > > This patch keeps matching cached PFNs in sync until a pageblock with > > isolation candidates is found. > > > > The actual benefit is marginal given that the sync scanner following the > > async scanner will often skip a number of pageblocks but it's useless > > work. Any benefit depends heavily on whether the scanners restarted > > recently so overall the reduction in scan rates is a mere 2.8% which > > is borderline noise. > > > > Signed-off-by: Mel Gorman <mgorman@techsingularity.net> > > Acked-by: Vlastimil Babka <vbabka@suse.cz> > > My easlier suggestion to check more thoroughly if pages can be migrated (which > depends on the mode) before isolating them wouldn't play nice with this :) > No, unfortunately it wouldn't. I did find though that sync_light often ran very quickly after async when compaction was having trouble succeeding. The time window was short enough that states like Dirty/Writeback were highly unlikely to be cleared. It might have played nice when fragmentation was very low but any benefit then would be very difficult to detect.
diff --git a/mm/compaction.c b/mm/compaction.c index 921720f7a416..be27e4fa1b40 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -1967,6 +1967,7 @@ static enum compact_result compact_zone(struct compact_control *cc) unsigned long end_pfn = zone_end_pfn(cc->zone); unsigned long last_migrated_pfn; const bool sync = cc->mode != MIGRATE_ASYNC; + bool update_cached; unsigned long a, b, c; cc->migratetype = gfpflags_to_migratetype(cc->gfp_mask); @@ -2019,6 +2020,17 @@ static enum compact_result compact_zone(struct compact_control *cc) last_migrated_pfn = 0; + /* + * Migrate has separate cached PFNs for ASYNC and SYNC* migration on + * the basis that some migrations will fail in ASYNC mode. However, + * if the cached PFNs match and pageblocks are skipped due to having + * no isolation candidates, then the sync state does not matter. + * Until a pageblock with isolation candidates is found, keep the + * cached PFNs in sync to avoid revisiting the same blocks. + */ + update_cached = !sync && + cc->zone->compact_cached_migrate_pfn[0] == cc->zone->compact_cached_migrate_pfn[1]; + trace_mm_compaction_begin(start_pfn, cc->migrate_pfn, cc->free_pfn, end_pfn, sync); @@ -2050,6 +2062,11 @@ static enum compact_result compact_zone(struct compact_control *cc) last_migrated_pfn = 0; goto out; case ISOLATE_NONE: + if (update_cached) { + cc->zone->compact_cached_migrate_pfn[1] = + cc->zone->compact_cached_migrate_pfn[0]; + } + /* * We haven't isolated and migrated anything, but * there might still be unflushed migrations from @@ -2057,6 +2074,7 @@ static enum compact_result compact_zone(struct compact_control *cc) */ goto check_drain; case ISOLATE_SUCCESS: + update_cached = false; last_migrated_pfn = start_pfn; ; }
Migrate has separate cached PFNs for ASYNC and SYNC* migration on the basis that some migrations will fail in ASYNC mode. However, if the cached PFNs match at the start of scanning and pageblocks are skipped due to having no isolation candidates, then the sync state does not matter. This patch keeps matching cached PFNs in sync until a pageblock with isolation candidates is found. The actual benefit is marginal given that the sync scanner following the async scanner will often skip a number of pageblocks but it's useless work. Any benefit depends heavily on whether the scanners restarted recently so overall the reduction in scan rates is a mere 2.8% which is borderline noise. Signed-off-by: Mel Gorman <mgorman@techsingularity.net> --- mm/compaction.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+)