perf_counter: provide an mlock threshold

Provide a threshold to relax the mlock accounting, increasing usability.

Each counter gets perf_counter_mlock_kb for free.

[ Impact: allow more mmap buffering ]

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
LKML-Reference: <20090505155437.112113632@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 19 insertions, 4 deletions

diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 6e6834e0587e..2d1342738305 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -44,6 +44,7 @@ static atomic_t nr_munmap_tracking __read_mostly;
 static atomic_t nr_comm_tracking __read_mostly;
 
 int sysctl_perf_counter_priv __read_mostly; /* do we need to be privileged */
+int sysctl_perf_counter_mlock __read_mostly = 128; /* 'free' kb per counter */
 
 /*
  * Lock for (sysadmin-configurable) counter reservations:
@@ -1461,7 +1462,7 @@ static void perf_mmap_close(struct vm_area_struct *vma)
 
         if (atomic_dec_and_mutex_lock(&counter->mmap_count,
                                       &counter->mmap_mutex)) {
-                vma->vm_mm->locked_vm -= counter->data->nr_pages + 1;
+                vma->vm_mm->locked_vm -= counter->data->nr_locked;
                 perf_mmap_data_free(counter);
                 mutex_unlock(&counter->mmap_mutex);
         }
@@ -1480,6 +1481,7 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
         unsigned long nr_pages;
         unsigned long locked, lock_limit;
         int ret = 0;
+        long extra;
 
         if (!(vma->vm_flags & VM_SHARED) || (vma->vm_flags & VM_WRITE))
                 return -EINVAL;
@@ -1507,8 +1509,12 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
                 goto unlock;
         }
 
-        locked = vma->vm_mm->locked_vm;
-        locked += nr_pages + 1;
+        extra = nr_pages /* + 1 only account the data pages */;
+        extra -= sysctl_perf_counter_mlock >> (PAGE_SHIFT - 10);
+        if (extra < 0)
+                extra = 0;
+
+        locked = vma->vm_mm->locked_vm + extra;
 
         lock_limit = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur;
         lock_limit >>= PAGE_SHIFT;
@@ -1524,7 +1530,8 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
                 goto unlock;
 
         atomic_set(&counter->mmap_count, 1);
-        vma->vm_mm->locked_vm += nr_pages + 1;
+        vma->vm_mm->locked_vm += extra;
+        counter->data->nr_locked = extra;
 unlock:
         mutex_unlock(&counter->mmap_mutex);
 
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 8203d70928d5..3b05c2b088d2 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -920,6 +920,14 @@ static struct ctl_table kern_table[] = {
                 .mode           = 0644,
                 .proc_handler   = &proc_dointvec,
         },
+        {
+                .ctl_name       = CTL_UNNUMBERED,
+                .procname       = "perf_counter_mlock_kb",
+                .data           = &sysctl_perf_counter_mlock,
+                .maxlen         = sizeof(sysctl_perf_counter_mlock),
+                .mode           = 0644,
+                .proc_handler   = &proc_dointvec,
+        },
 #endif
 /*
  * NOTE: do not add new entries to this table unless you have read