| Message ID | 20200527173608.2885243-7-daniel.m.jordan@oracle.com (mailing list archive) |
|---|---|
| State | Not Applicable |
| Delegated to: | Herbert Xu |
| Headers | show |
| Series | padata: parallelize deferred page init | expand |
On Wed, May 27, 2020 at 10:37 AM Daniel Jordan <daniel.m.jordan@oracle.com> wrote: > > Deferred struct page init is a significant bottleneck in kernel boot. > Optimizing it maximizes availability for large-memory systems and allows > spinning up short-lived VMs as needed without having to leave them > running. It also benefits bare metal machines hosting VMs that are > sensitive to downtime. In projects such as VMM Fast Restart[1], where > guest state is preserved across kexec reboot, it helps prevent > application and network timeouts in the guests. > > Multithread to take full advantage of system memory bandwidth. > > The maximum number of threads is capped at the number of CPUs on the > node because speedups always improve with additional threads on every > system tested, and at this phase of boot, the system is otherwise idle > and waiting on page init to finish. > > Helper threads operate on section-aligned ranges to both avoid false > sharing when setting the pageblock's migrate type and to avoid accessing > uninitialized buddy pages, though max order alignment is enough for the > latter. > > The minimum chunk size is also a section. There was benefit to using > multiple threads even on relatively small memory (1G) systems, and this > is the smallest size that the alignment allows. > > The time (milliseconds) is the slowest node to initialize since boot > blocks until all nodes finish. intel_pstate is loaded in active mode > without hwp and with turbo enabled, and intel_idle is active as well. > > Intel(R) Xeon(R) Platinum 8167M CPU @ 2.00GHz (Skylake, bare metal) > 2 nodes * 26 cores * 2 threads = 104 CPUs > 384G/node = 768G memory > > kernel boot deferred init > ------------------------ ------------------------ > node% (thr) speedup time_ms (stdev) speedup time_ms (stdev) > ( 0) -- 4089.7 ( 8.1) -- 1785.7 ( 7.6) > 2% ( 1) 1.7% 4019.3 ( 1.5) 3.8% 1717.7 ( 11.8) > 12% ( 6) 34.9% 2662.7 ( 2.9) 79.9% 359.3 ( 0.6) > 25% ( 13) 39.9% 2459.0 ( 3.6) 91.2% 157.0 ( 0.0) > 37% ( 19) 39.2% 2485.0 ( 29.7) 90.4% 172.0 ( 28.6) > 50% ( 26) 39.3% 2482.7 ( 25.7) 90.3% 173.7 ( 30.0) > 75% ( 39) 39.0% 2495.7 ( 5.5) 89.4% 190.0 ( 1.0) > 100% ( 52) 40.2% 2443.7 ( 3.8) 92.3% 138.0 ( 1.0) > > Intel(R) Xeon(R) CPU E5-2699C v4 @ 2.20GHz (Broadwell, kvm guest) > 1 node * 16 cores * 2 threads = 32 CPUs > 192G/node = 192G memory > > kernel boot deferred init > ------------------------ ------------------------ > node% (thr) speedup time_ms (stdev) speedup time_ms (stdev) > ( 0) -- 1988.7 ( 9.6) -- 1096.0 ( 11.5) > 3% ( 1) 1.1% 1967.0 ( 17.6) 0.3% 1092.7 ( 11.0) > 12% ( 4) 41.1% 1170.3 ( 14.2) 73.8% 287.0 ( 3.6) > 25% ( 8) 47.1% 1052.7 ( 21.9) 83.9% 177.0 ( 13.5) > 38% ( 12) 48.9% 1016.3 ( 12.1) 86.8% 144.7 ( 1.5) > 50% ( 16) 48.9% 1015.7 ( 8.1) 87.8% 134.0 ( 4.4) > 75% ( 24) 49.1% 1012.3 ( 3.1) 88.1% 130.3 ( 2.3) > 100% ( 32) 49.5% 1004.0 ( 5.3) 88.5% 125.7 ( 2.1) > > Intel(R) Xeon(R) CPU E5-2699 v3 @ 2.30GHz (Haswell, bare metal) > 2 nodes * 18 cores * 2 threads = 72 CPUs > 128G/node = 256G memory > > kernel boot deferred init > ------------------------ ------------------------ > node% (thr) speedup time_ms (stdev) speedup time_ms (stdev) > ( 0) -- 1680.0 ( 4.6) -- 627.0 ( 4.0) > 3% ( 1) 0.3% 1675.7 ( 4.5) -0.2% 628.0 ( 3.6) > 11% ( 4) 25.6% 1250.7 ( 2.1) 67.9% 201.0 ( 0.0) > 25% ( 9) 30.7% 1164.0 ( 17.3) 81.8% 114.3 ( 17.7) > 36% ( 13) 31.4% 1152.7 ( 10.8) 84.0% 100.3 ( 17.9) > 50% ( 18) 31.5% 1150.7 ( 9.3) 83.9% 101.0 ( 14.1) > 75% ( 27) 31.7% 1148.0 ( 5.6) 84.5% 97.3 ( 6.4) > 100% ( 36) 32.0% 1142.3 ( 4.0) 85.6% 90.0 ( 1.0) > > AMD EPYC 7551 32-Core Processor (Zen, kvm guest) > 1 node * 8 cores * 2 threads = 16 CPUs > 64G/node = 64G memory > > kernel boot deferred init > ------------------------ ------------------------ > node% (thr) speedup time_ms (stdev) speedup time_ms (stdev) > ( 0) -- 1029.3 ( 25.1) -- 240.7 ( 1.5) > 6% ( 1) -0.6% 1036.0 ( 7.8) -2.2% 246.0 ( 0.0) > 12% ( 2) 11.8% 907.7 ( 8.6) 44.7% 133.0 ( 1.0) > 25% ( 4) 13.9% 886.0 ( 10.6) 62.6% 90.0 ( 6.0) > 38% ( 6) 17.8% 845.7 ( 14.2) 69.1% 74.3 ( 3.8) > 50% ( 8) 16.8% 856.0 ( 22.1) 72.9% 65.3 ( 5.7) > 75% ( 12) 15.4% 871.0 ( 29.2) 79.8% 48.7 ( 7.4) > 100% ( 16) 21.0% 813.7 ( 21.0) 80.5% 47.0 ( 5.2) > > Server-oriented distros that enable deferred page init sometimes run in > small VMs, and they still benefit even though the fraction of boot time > saved is smaller: > > AMD EPYC 7551 32-Core Processor (Zen, kvm guest) > 1 node * 2 cores * 2 threads = 4 CPUs > 16G/node = 16G memory > > kernel boot deferred init > ------------------------ ------------------------ > node% (thr) speedup time_ms (stdev) speedup time_ms (stdev) > ( 0) -- 716.0 ( 14.0) -- 49.7 ( 0.6) > 25% ( 1) 1.8% 703.0 ( 5.3) -4.0% 51.7 ( 0.6) > 50% ( 2) 1.6% 704.7 ( 1.2) 43.0% 28.3 ( 0.6) > 75% ( 3) 2.7% 696.7 ( 13.1) 49.7% 25.0 ( 0.0) > 100% ( 4) 4.1% 687.0 ( 10.4) 55.7% 22.0 ( 0.0) > > Intel(R) Xeon(R) CPU E5-2699 v3 @ 2.30GHz (Haswell, kvm guest) > 1 node * 2 cores * 2 threads = 4 CPUs > 14G/node = 14G memory > > kernel boot deferred init > ------------------------ ------------------------ > node% (thr) speedup time_ms (stdev) speedup time_ms (stdev) > ( 0) -- 787.7 ( 6.4) -- 122.3 ( 0.6) > 25% ( 1) 0.2% 786.3 ( 10.8) -2.5% 125.3 ( 2.1) > 50% ( 2) 5.9% 741.0 ( 13.9) 37.6% 76.3 ( 19.7) > 75% ( 3) 8.3% 722.0 ( 19.0) 49.9% 61.3 ( 3.2) > 100% ( 4) 9.3% 714.7 ( 9.5) 56.4% 53.3 ( 1.5) > > On Josh's 96-CPU and 192G memory system: > > Without this patch series: > [ 0.487132] node 0 initialised, 23398907 pages in 292ms > [ 0.499132] node 1 initialised, 24189223 pages in 304ms > ... > [ 0.629376] Run /sbin/init as init process > > With this patch series: > [ 0.231435] node 1 initialised, 24189223 pages in 32ms > [ 0.236718] node 0 initialised, 23398907 pages in 36ms > > [1] https://static.sched.com/hosted_files/kvmforum2019/66/VMM-fast-restart_kvmforum2019.pdf > > Signed-off-by: Daniel Jordan <daniel.m.jordan@oracle.com> > Tested-by: Josh Triplett <josh@joshtriplett.org> > --- > mm/Kconfig | 6 +++--- > mm/page_alloc.c | 46 ++++++++++++++++++++++++++++++++++++++++------ > 2 files changed, 43 insertions(+), 9 deletions(-) > > diff --git a/mm/Kconfig b/mm/Kconfig > index c1acc34c1c358..04c1da3f9f44c 100644 > --- a/mm/Kconfig > +++ b/mm/Kconfig > @@ -750,13 +750,13 @@ config DEFERRED_STRUCT_PAGE_INIT > depends on SPARSEMEM > depends on !NEED_PER_CPU_KM > depends on 64BIT > + select PADATA > help > Ordinarily all struct pages are initialised during early boot in a > single thread. On very large machines this can take a considerable > amount of time. If this option is set, large machines will bring up > - a subset of memmap at boot and then initialise the rest in parallel > - by starting one-off "pgdatinitX" kernel thread for each node X. This > - has a potential performance impact on processes running early in the > + a subset of memmap at boot and then initialise the rest in parallel. > + This has a potential performance impact on tasks running early in the > lifetime of the system until these kthreads finish the > initialisation. > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index d64f3027fdfa6..1d47016849531 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -68,6 +68,7 @@ > #include <linux/lockdep.h> > #include <linux/nmi.h> > #include <linux/psi.h> > +#include <linux/padata.h> > > #include <asm/sections.h> > #include <asm/tlbflush.h> > @@ -1814,6 +1815,26 @@ deferred_init_maxorder(u64 *i, struct zone *zone, unsigned long *start_pfn, > return nr_pages; > } > > +static void __init > +deferred_init_memmap_chunk(unsigned long start_pfn, unsigned long end_pfn, > + void *arg) > +{ > + unsigned long spfn, epfn; > + struct zone *zone = arg; > + u64 i; > + > + deferred_init_mem_pfn_range_in_zone(&i, zone, &spfn, &epfn, start_pfn); > + > + /* > + * Initialize and free pages in MAX_ORDER sized increments so that we > + * can avoid introducing any issues with the buddy allocator. > + */ > + while (spfn < end_pfn) { > + deferred_init_maxorder(&i, zone, &spfn, &epfn); > + cond_resched(); > + } > +} > + > /* Initialise remaining memory on a node */ > static int __init deferred_init_memmap(void *data) > { > @@ -1823,7 +1844,7 @@ static int __init deferred_init_memmap(void *data) > unsigned long first_init_pfn, flags; > unsigned long start = jiffies; > struct zone *zone; > - int zid; > + int zid, max_threads; > u64 i; > > /* Bind memory initialisation thread to a local node if possible */ > @@ -1863,13 +1884,26 @@ static int __init deferred_init_memmap(void *data) > goto zone_empty; > > /* > - * Initialize and free pages in MAX_ORDER sized increments so > - * that we can avoid introducing any issues with the buddy > - * allocator. > + * More CPUs always led to greater speedups on tested systems, up to > + * all the nodes' CPUs. Use all since the system is otherwise idle now. > */ > + max_threads = max(cpumask_weight(cpumask), 1u); > + > while (spfn < epfn) { > - deferred_init_maxorder(&i, zone, &spfn, &epfn); > - cond_resched(); > + unsigned long epfn_align = ALIGN(epfn, PAGES_PER_SECTION); > + struct padata_mt_job job = { > + .thread_fn = deferred_init_memmap_chunk, > + .fn_arg = zone, > + .start = spfn, > + .size = epfn_align - spfn, > + .align = PAGES_PER_SECTION, > + .min_chunk = PAGES_PER_SECTION, > + .max_threads = max_threads, > + }; > + > + padata_do_multithreaded(&job); > + deferred_init_mem_pfn_range_in_zone(&i, zone, &spfn, &epfn, > + epfn_align); > } > zone_empty: > /* Sanity check that the next zone really is unpopulated */ So I am not a huge fan of using deferred_init_mem_pfn_range_in zone simply for the fact that we end up essentially discarding the i value and will have to walk the list repeatedly. However I don't think the overhead will be that great as I suspect there aren't going to be systems with that many ranges. So this is probably fine. Reviewed-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
diff --git a/mm/Kconfig b/mm/Kconfig index c1acc34c1c358..04c1da3f9f44c 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -750,13 +750,13 @@ config DEFERRED_STRUCT_PAGE_INIT depends on SPARSEMEM depends on !NEED_PER_CPU_KM depends on 64BIT + select PADATA help Ordinarily all struct pages are initialised during early boot in a single thread. On very large machines this can take a considerable amount of time. If this option is set, large machines will bring up - a subset of memmap at boot and then initialise the rest in parallel - by starting one-off "pgdatinitX" kernel thread for each node X. This - has a potential performance impact on processes running early in the + a subset of memmap at boot and then initialise the rest in parallel. + This has a potential performance impact on tasks running early in the lifetime of the system until these kthreads finish the initialisation. diff --git a/mm/page_alloc.c b/mm/page_alloc.c index d64f3027fdfa6..1d47016849531 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -68,6 +68,7 @@ #include <linux/lockdep.h> #include <linux/nmi.h> #include <linux/psi.h> +#include <linux/padata.h> #include <asm/sections.h> #include <asm/tlbflush.h> @@ -1814,6 +1815,26 @@ deferred_init_maxorder(u64 *i, struct zone *zone, unsigned long *start_pfn, return nr_pages; } +static void __init +deferred_init_memmap_chunk(unsigned long start_pfn, unsigned long end_pfn, + void *arg) +{ + unsigned long spfn, epfn; + struct zone *zone = arg; + u64 i; + + deferred_init_mem_pfn_range_in_zone(&i, zone, &spfn, &epfn, start_pfn); + + /* + * Initialize and free pages in MAX_ORDER sized increments so that we + * can avoid introducing any issues with the buddy allocator. + */ + while (spfn < end_pfn) { + deferred_init_maxorder(&i, zone, &spfn, &epfn); + cond_resched(); + } +} + /* Initialise remaining memory on a node */ static int __init deferred_init_memmap(void *data) { @@ -1823,7 +1844,7 @@ static int __init deferred_init_memmap(void *data) unsigned long first_init_pfn, flags; unsigned long start = jiffies; struct zone *zone; - int zid; + int zid, max_threads; u64 i; /* Bind memory initialisation thread to a local node if possible */ @@ -1863,13 +1884,26 @@ static int __init deferred_init_memmap(void *data) goto zone_empty; /* - * Initialize and free pages in MAX_ORDER sized increments so - * that we can avoid introducing any issues with the buddy - * allocator. + * More CPUs always led to greater speedups on tested systems, up to + * all the nodes' CPUs. Use all since the system is otherwise idle now. */ + max_threads = max(cpumask_weight(cpumask), 1u); + while (spfn < epfn) { - deferred_init_maxorder(&i, zone, &spfn, &epfn); - cond_resched(); + unsigned long epfn_align = ALIGN(epfn, PAGES_PER_SECTION); + struct padata_mt_job job = { + .thread_fn = deferred_init_memmap_chunk, + .fn_arg = zone, + .start = spfn, + .size = epfn_align - spfn, + .align = PAGES_PER_SECTION, + .min_chunk = PAGES_PER_SECTION, + .max_threads = max_threads, + }; + + padata_do_multithreaded(&job); + deferred_init_mem_pfn_range_in_zone(&i, zone, &spfn, &epfn, + epfn_align); } zone_empty: /* Sanity check that the next zone really is unpopulated */
Deferred struct page init is a significant bottleneck in kernel boot. Optimizing it maximizes availability for large-memory systems and allows spinning up short-lived VMs as needed without having to leave them running. It also benefits bare metal machines hosting VMs that are sensitive to downtime. In projects such as VMM Fast Restart[1], where guest state is preserved across kexec reboot, it helps prevent application and network timeouts in the guests. Multithread to take full advantage of system memory bandwidth. The maximum number of threads is capped at the number of CPUs on the node because speedups always improve with additional threads on every system tested, and at this phase of boot, the system is otherwise idle and waiting on page init to finish. Helper threads operate on section-aligned ranges to both avoid false sharing when setting the pageblock's migrate type and to avoid accessing uninitialized buddy pages, though max order alignment is enough for the latter. The minimum chunk size is also a section. There was benefit to using multiple threads even on relatively small memory (1G) systems, and this is the smallest size that the alignment allows. The time (milliseconds) is the slowest node to initialize since boot blocks until all nodes finish. intel_pstate is loaded in active mode without hwp and with turbo enabled, and intel_idle is active as well. Intel(R) Xeon(R) Platinum 8167M CPU @ 2.00GHz (Skylake, bare metal) 2 nodes * 26 cores * 2 threads = 104 CPUs 384G/node = 768G memory kernel boot deferred init ------------------------ ------------------------ node% (thr) speedup time_ms (stdev) speedup time_ms (stdev) ( 0) -- 4089.7 ( 8.1) -- 1785.7 ( 7.6) 2% ( 1) 1.7% 4019.3 ( 1.5) 3.8% 1717.7 ( 11.8) 12% ( 6) 34.9% 2662.7 ( 2.9) 79.9% 359.3 ( 0.6) 25% ( 13) 39.9% 2459.0 ( 3.6) 91.2% 157.0 ( 0.0) 37% ( 19) 39.2% 2485.0 ( 29.7) 90.4% 172.0 ( 28.6) 50% ( 26) 39.3% 2482.7 ( 25.7) 90.3% 173.7 ( 30.0) 75% ( 39) 39.0% 2495.7 ( 5.5) 89.4% 190.0 ( 1.0) 100% ( 52) 40.2% 2443.7 ( 3.8) 92.3% 138.0 ( 1.0) Intel(R) Xeon(R) CPU E5-2699C v4 @ 2.20GHz (Broadwell, kvm guest) 1 node * 16 cores * 2 threads = 32 CPUs 192G/node = 192G memory kernel boot deferred init ------------------------ ------------------------ node% (thr) speedup time_ms (stdev) speedup time_ms (stdev) ( 0) -- 1988.7 ( 9.6) -- 1096.0 ( 11.5) 3% ( 1) 1.1% 1967.0 ( 17.6) 0.3% 1092.7 ( 11.0) 12% ( 4) 41.1% 1170.3 ( 14.2) 73.8% 287.0 ( 3.6) 25% ( 8) 47.1% 1052.7 ( 21.9) 83.9% 177.0 ( 13.5) 38% ( 12) 48.9% 1016.3 ( 12.1) 86.8% 144.7 ( 1.5) 50% ( 16) 48.9% 1015.7 ( 8.1) 87.8% 134.0 ( 4.4) 75% ( 24) 49.1% 1012.3 ( 3.1) 88.1% 130.3 ( 2.3) 100% ( 32) 49.5% 1004.0 ( 5.3) 88.5% 125.7 ( 2.1) Intel(R) Xeon(R) CPU E5-2699 v3 @ 2.30GHz (Haswell, bare metal) 2 nodes * 18 cores * 2 threads = 72 CPUs 128G/node = 256G memory kernel boot deferred init ------------------------ ------------------------ node% (thr) speedup time_ms (stdev) speedup time_ms (stdev) ( 0) -- 1680.0 ( 4.6) -- 627.0 ( 4.0) 3% ( 1) 0.3% 1675.7 ( 4.5) -0.2% 628.0 ( 3.6) 11% ( 4) 25.6% 1250.7 ( 2.1) 67.9% 201.0 ( 0.0) 25% ( 9) 30.7% 1164.0 ( 17.3) 81.8% 114.3 ( 17.7) 36% ( 13) 31.4% 1152.7 ( 10.8) 84.0% 100.3 ( 17.9) 50% ( 18) 31.5% 1150.7 ( 9.3) 83.9% 101.0 ( 14.1) 75% ( 27) 31.7% 1148.0 ( 5.6) 84.5% 97.3 ( 6.4) 100% ( 36) 32.0% 1142.3 ( 4.0) 85.6% 90.0 ( 1.0) AMD EPYC 7551 32-Core Processor (Zen, kvm guest) 1 node * 8 cores * 2 threads = 16 CPUs 64G/node = 64G memory kernel boot deferred init ------------------------ ------------------------ node% (thr) speedup time_ms (stdev) speedup time_ms (stdev) ( 0) -- 1029.3 ( 25.1) -- 240.7 ( 1.5) 6% ( 1) -0.6% 1036.0 ( 7.8) -2.2% 246.0 ( 0.0) 12% ( 2) 11.8% 907.7 ( 8.6) 44.7% 133.0 ( 1.0) 25% ( 4) 13.9% 886.0 ( 10.6) 62.6% 90.0 ( 6.0) 38% ( 6) 17.8% 845.7 ( 14.2) 69.1% 74.3 ( 3.8) 50% ( 8) 16.8% 856.0 ( 22.1) 72.9% 65.3 ( 5.7) 75% ( 12) 15.4% 871.0 ( 29.2) 79.8% 48.7 ( 7.4) 100% ( 16) 21.0% 813.7 ( 21.0) 80.5% 47.0 ( 5.2) Server-oriented distros that enable deferred page init sometimes run in small VMs, and they still benefit even though the fraction of boot time saved is smaller: AMD EPYC 7551 32-Core Processor (Zen, kvm guest) 1 node * 2 cores * 2 threads = 4 CPUs 16G/node = 16G memory kernel boot deferred init ------------------------ ------------------------ node% (thr) speedup time_ms (stdev) speedup time_ms (stdev) ( 0) -- 716.0 ( 14.0) -- 49.7 ( 0.6) 25% ( 1) 1.8% 703.0 ( 5.3) -4.0% 51.7 ( 0.6) 50% ( 2) 1.6% 704.7 ( 1.2) 43.0% 28.3 ( 0.6) 75% ( 3) 2.7% 696.7 ( 13.1) 49.7% 25.0 ( 0.0) 100% ( 4) 4.1% 687.0 ( 10.4) 55.7% 22.0 ( 0.0) Intel(R) Xeon(R) CPU E5-2699 v3 @ 2.30GHz (Haswell, kvm guest) 1 node * 2 cores * 2 threads = 4 CPUs 14G/node = 14G memory kernel boot deferred init ------------------------ ------------------------ node% (thr) speedup time_ms (stdev) speedup time_ms (stdev) ( 0) -- 787.7 ( 6.4) -- 122.3 ( 0.6) 25% ( 1) 0.2% 786.3 ( 10.8) -2.5% 125.3 ( 2.1) 50% ( 2) 5.9% 741.0 ( 13.9) 37.6% 76.3 ( 19.7) 75% ( 3) 8.3% 722.0 ( 19.0) 49.9% 61.3 ( 3.2) 100% ( 4) 9.3% 714.7 ( 9.5) 56.4% 53.3 ( 1.5) On Josh's 96-CPU and 192G memory system: Without this patch series: [ 0.487132] node 0 initialised, 23398907 pages in 292ms [ 0.499132] node 1 initialised, 24189223 pages in 304ms ... [ 0.629376] Run /sbin/init as init process With this patch series: [ 0.231435] node 1 initialised, 24189223 pages in 32ms [ 0.236718] node 0 initialised, 23398907 pages in 36ms [1] https://static.sched.com/hosted_files/kvmforum2019/66/VMM-fast-restart_kvmforum2019.pdf Signed-off-by: Daniel Jordan <daniel.m.jordan@oracle.com> Tested-by: Josh Triplett <josh@joshtriplett.org> --- mm/Kconfig | 6 +++--- mm/page_alloc.c | 46 ++++++++++++++++++++++++++++++++++++++++------ 2 files changed, 43 insertions(+), 9 deletions(-)