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>
diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 6e6834e..2d13427 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -44,6 +44,7 @@
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 @@
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 @@
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 @@
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 @@
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 8203d70..3b05c2b 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -920,6 +920,14 @@
.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