mm: numa: return the number of base pages altered by protection changes

Commit 0255d4918480 ("mm: Account for a THP NUMA hinting update as one
PTE update") was added to account for the number of PTE updates when
marking pages prot_numa.  task_numa_work was using the old return value
to track how much address space had been updated.  Altering the return
value causes the scanner to do more work than it is configured or
documented to in a single unit of work.

This patch reverts that commit and accounts for the number of THP
updates separately in vmstat.  It is up to the administrator to
interpret the pair of values correctly.  This is a straight-forward
operation and likely to only be of interest when actively debugging NUMA
balancing problems.

The impact of this patch is that the NUMA PTE scanner will scan slower
when THP is enabled and workloads may converge slower as a result.  On
the flip size system CPU usage should be lower than recent tests
reported.  This is an illustrative example of a short single JVM specjbb
test

specjbb
                       3.12.0                3.12.0
                      vanilla      acctupdates
TPut 1      26143.00 (  0.00%)     25747.00 ( -1.51%)
TPut 7     185257.00 (  0.00%)    183202.00 ( -1.11%)
TPut 13    329760.00 (  0.00%)    346577.00 (  5.10%)
TPut 19    442502.00 (  0.00%)    460146.00 (  3.99%)
TPut 25    540634.00 (  0.00%)    549053.00 (  1.56%)
TPut 31    512098.00 (  0.00%)    519611.00 (  1.47%)
TPut 37    461276.00 (  0.00%)    474973.00 (  2.97%)
TPut 43    403089.00 (  0.00%)    414172.00 (  2.75%)

              3.12.0      3.12.0
             vanillaacctupdates
User         5169.64     5184.14
System        100.45       80.02
Elapsed       252.75      251.85

Performance is similar but note the reduction in system CPU time.  While
this showed a performance gain, it will not be universal but at least
it'll be behaving as documented.  The vmstats are obviously different but
here is an obvious interpretation of them from mmtests.

                                3.12.0      3.12.0
                               vanillaacctupdates
NUMA page range updates        1408326    11043064
NUMA huge PMD updates                0       21040
NUMA PTE updates               1408326      291624

"NUMA page range updates" == nr_pte_updates and is the value returned to
the NUMA pte scanner.  NUMA huge PMD updates were the number of THP
updates which in combination can be used to calculate how many ptes were
updated from userspace.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Reported-by: Alex Thorlton <athorlton@sgi.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
index 1855f0a22add848202b693a16d103072a8f3487a..c557c6d096def9a93bb5b00af4df87166539e048 100644 (file)
--- a/include/linux/vm_event_item.h
+++ b/include/linux/vm_event_item.h
@@ -39,6 +39,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
                PAGEOUTRUN, ALLOCSTALL, PGROTATED,
 #ifdef CONFIG_NUMA_BALANCING
                NUMA_PTE_UPDATES,
+               NUMA_HUGE_PTE_UPDATES,
                NUMA_HINT_FAULTS,
                NUMA_HINT_FAULTS_LOCAL,
                NUMA_PAGE_MIGRATE,

diff --git a/mm/mprotect.c b/mm/mprotect.c
index a597f2ffcd6fc873a5f5b9779e4e79ac022bb2fe..26667971c824b08ca3dae7188a965e1e4efe0b79 100644 (file)
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -112,6 +112,7 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
        pmd_t *pmd;
        unsigned long next;
        unsigned long pages = 0;
+       unsigned long nr_huge_updates = 0;
 
        pmd = pmd_offset(pud, addr);
        do {
@@ -126,9 +127,10 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
                                                newprot, prot_numa);
 
                                if (nr_ptes) {
-                                       if (nr_ptes == HPAGE_PMD_NR)
-                                               pages++;
-
+                                       if (nr_ptes == HPAGE_PMD_NR) {
+                                               pages += HPAGE_PMD_NR;
+                                               nr_huge_updates++;
+                                       }
                                        continue;
                                }
                        }
@@ -141,6 +143,8 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
                pages += this_pages;
        } while (pmd++, addr = next, addr != end);
 
+       if (nr_huge_updates)
+               count_vm_numa_events(NUMA_HUGE_PTE_UPDATES, nr_huge_updates);
        return pages;
 }
 

diff --git a/mm/vmstat.c b/mm/vmstat.c
index b6d17edf8cf34c191b77b6bdf07d3ee41e0de2ce..72496140ac0843e54c086c18ace843189b47ffda 100644 (file)
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -812,6 +812,7 @@ const char * const vmstat_text[] = {
 
 #ifdef CONFIG_NUMA_BALANCING
        "numa_pte_updates",
+       "numa_huge_pte_updates",
        "numa_hint_faults",
        "numa_hint_faults_local",
        "numa_pages_migrated",