| Message ID | 20181214230310.572-7-mgorman@techsingularity.net (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Increase success rates and reduce latency of compaction v1 | expand |
On 12/15/18 12:03 AM, Mel Gorman wrote: > Pages with no migration handler use a fallback hander which sometimes > works and sometimes persistently fails such as blockdev pages. Migration > will retry a number of times on these persistent pages which is wasteful > during compaction. This patch will fail migration immediately unless the > caller is in MIGRATE_SYNC mode which indicates the caller is willing to > wait while being persistent. Right. > This is not expected to help THP allocation success rates but it does > reduce latencies slightly. > > 1-socket thpfioscale > 4.20.0-rc6 4.20.0-rc6 > noreserved-v1r4 failfast-v1r4 > Amean fault-both-1 0.00 ( 0.00%) 0.00 * 0.00%* > Amean fault-both-3 2276.15 ( 0.00%) 3867.54 * -69.92%* This is rather weird. > Amean fault-both-5 4992.20 ( 0.00%) 5313.20 ( -6.43%) > Amean fault-both-7 7373.30 ( 0.00%) 7039.11 ( 4.53%) > Amean fault-both-12 11911.52 ( 0.00%) 11328.29 ( 4.90%) > Amean fault-both-18 17209.42 ( 0.00%) 16455.34 ( 4.38%) > Amean fault-both-24 20943.71 ( 0.00%) 20448.94 ( 2.36%) > Amean fault-both-30 22703.00 ( 0.00%) 21655.07 ( 4.62%) > Amean fault-both-32 22461.41 ( 0.00%) 21415.35 ( 4.66%) > > The 2-socket results are not materially different. Scan rates are > similar as expected. > > Signed-off-by: Mel Gorman <mgorman@techsingularity.net> Acked-by: Vlastimil Babka <vbabka@suse.cz> > --- > mm/migrate.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/migrate.c b/mm/migrate.c > index df17a710e2c7..0e27a10429e2 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -885,7 +885,7 @@ static int fallback_migrate_page(struct address_space *mapping, > */ > if (page_has_private(page) && > !try_to_release_page(page, GFP_KERNEL)) > - return -EAGAIN; > + return mode == MIGRATE_SYNC ? -EAGAIN : -EBUSY; > > return migrate_page(mapping, newpage, page, mode); > } >
On Tue, Dec 18, 2018 at 10:06:31AM +0100, Vlastimil Babka wrote: > On 12/15/18 12:03 AM, Mel Gorman wrote: > > Pages with no migration handler use a fallback hander which sometimes > > works and sometimes persistently fails such as blockdev pages. Migration > > will retry a number of times on these persistent pages which is wasteful > > during compaction. This patch will fail migration immediately unless the > > caller is in MIGRATE_SYNC mode which indicates the caller is willing to > > wait while being persistent. > > Right. > > > This is not expected to help THP allocation success rates but it does > > reduce latencies slightly. > > > > 1-socket thpfioscale > > 4.20.0-rc6 4.20.0-rc6 > > noreserved-v1r4 failfast-v1r4 > > Amean fault-both-1 0.00 ( 0.00%) 0.00 * 0.00%* > > Amean fault-both-3 2276.15 ( 0.00%) 3867.54 * -69.92%* > > This is rather weird. > Fault latency is extremely variable and there can be very large outliers that skew the mean (the full report includes quartiles but it makes for an excessive changelog). It can be down to luck about how often the migrate scanner advances and how often it gets reset. For this series, it'll not be unusual to see jitter in the latencies for individual patches that will not get nailed down reliably until later in the series. The alternative is massive patches that do multiple things which will look nice in changelogs and be horrible to review. > > Amean fault-both-5 4992.20 ( 0.00%) 5313.20 ( -6.43%) > > Amean fault-both-7 7373.30 ( 0.00%) 7039.11 ( 4.53%) > > Amean fault-both-12 11911.52 ( 0.00%) 11328.29 ( 4.90%) > > Amean fault-both-18 17209.42 ( 0.00%) 16455.34 ( 4.38%) > > Amean fault-both-24 20943.71 ( 0.00%) 20448.94 ( 2.36%) > > Amean fault-both-30 22703.00 ( 0.00%) 21655.07 ( 4.62%) > > Amean fault-both-32 22461.41 ( 0.00%) 21415.35 ( 4.66%) > > > > The 2-socket results are not materially different. Scan rates are > > similar as expected. > > > > Signed-off-by: Mel Gorman <mgorman@techsingularity.net> > > Acked-by: Vlastimil Babka <vbabka@suse.cz> > Thanks.
On Fri, Dec 14, 2018 at 3:03 PM Mel Gorman <mgorman@techsingularity.net> wrote: > > Pages with no migration handler use a fallback hander which sometimes > works and sometimes persistently fails such as blockdev pages. Migration A minor correction. The above statement sounds not accurate anymore since Jan Kara had patch series (blkdev: avoid migration stalls for blkdev pages) have blockdev use its own migration handler. Thanks, Yang > will retry a number of times on these persistent pages which is wasteful > during compaction. This patch will fail migration immediately unless the > caller is in MIGRATE_SYNC mode which indicates the caller is willing to > wait while being persistent. > > This is not expected to help THP allocation success rates but it does > reduce latencies slightly. > > 1-socket thpfioscale > 4.20.0-rc6 4.20.0-rc6 > noreserved-v1r4 failfast-v1r4 > Amean fault-both-1 0.00 ( 0.00%) 0.00 * 0.00%* > Amean fault-both-3 2276.15 ( 0.00%) 3867.54 * -69.92%* > Amean fault-both-5 4992.20 ( 0.00%) 5313.20 ( -6.43%) > Amean fault-both-7 7373.30 ( 0.00%) 7039.11 ( 4.53%) > Amean fault-both-12 11911.52 ( 0.00%) 11328.29 ( 4.90%) > Amean fault-both-18 17209.42 ( 0.00%) 16455.34 ( 4.38%) > Amean fault-both-24 20943.71 ( 0.00%) 20448.94 ( 2.36%) > Amean fault-both-30 22703.00 ( 0.00%) 21655.07 ( 4.62%) > Amean fault-both-32 22461.41 ( 0.00%) 21415.35 ( 4.66%) > > The 2-socket results are not materially different. Scan rates are > similar as expected. > > Signed-off-by: Mel Gorman <mgorman@techsingularity.net> > --- > mm/migrate.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/migrate.c b/mm/migrate.c > index df17a710e2c7..0e27a10429e2 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -885,7 +885,7 @@ static int fallback_migrate_page(struct address_space *mapping, > */ > if (page_has_private(page) && > !try_to_release_page(page, GFP_KERNEL)) > - return -EAGAIN; > + return mode == MIGRATE_SYNC ? -EAGAIN : -EBUSY; > > return migrate_page(mapping, newpage, page, mode); > } > -- > 2.16.4 >
On Thu, Dec 20, 2018 at 11:44:57AM -0800, Yang Shi wrote: > On Fri, Dec 14, 2018 at 3:03 PM Mel Gorman <mgorman@techsingularity.net> wrote: > > > > Pages with no migration handler use a fallback hander which sometimes > > works and sometimes persistently fails such as blockdev pages. Migration > > A minor correction. The above statement sounds not accurate anymore > since Jan Kara had patch series (blkdev: avoid migration stalls for > blkdev pages) have blockdev use its own migration handler. > I'm aware given that I reviewed that series. The statement was correct at the time of writing. I'll alter the example when rebased on top of Jan's work.
diff --git a/mm/migrate.c b/mm/migrate.c index df17a710e2c7..0e27a10429e2 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -885,7 +885,7 @@ static int fallback_migrate_page(struct address_space *mapping, */ if (page_has_private(page) && !try_to_release_page(page, GFP_KERNEL)) - return -EAGAIN; + return mode == MIGRATE_SYNC ? -EAGAIN : -EBUSY; return migrate_page(mapping, newpage, page, mode); }
Pages with no migration handler use a fallback hander which sometimes works and sometimes persistently fails such as blockdev pages. Migration will retry a number of times on these persistent pages which is wasteful during compaction. This patch will fail migration immediately unless the caller is in MIGRATE_SYNC mode which indicates the caller is willing to wait while being persistent. This is not expected to help THP allocation success rates but it does reduce latencies slightly. 1-socket thpfioscale 4.20.0-rc6 4.20.0-rc6 noreserved-v1r4 failfast-v1r4 Amean fault-both-1 0.00 ( 0.00%) 0.00 * 0.00%* Amean fault-both-3 2276.15 ( 0.00%) 3867.54 * -69.92%* Amean fault-both-5 4992.20 ( 0.00%) 5313.20 ( -6.43%) Amean fault-both-7 7373.30 ( 0.00%) 7039.11 ( 4.53%) Amean fault-both-12 11911.52 ( 0.00%) 11328.29 ( 4.90%) Amean fault-both-18 17209.42 ( 0.00%) 16455.34 ( 4.38%) Amean fault-both-24 20943.71 ( 0.00%) 20448.94 ( 2.36%) Amean fault-both-30 22703.00 ( 0.00%) 21655.07 ( 4.62%) Amean fault-both-32 22461.41 ( 0.00%) 21415.35 ( 4.66%) The 2-socket results are not materially different. Scan rates are similar as expected. Signed-off-by: Mel Gorman <mgorman@techsingularity.net> --- mm/migrate.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)