Re: [RFC 1/3] /dev/low_mem_notify
From: Jonathan Corbet <corbet@lwn.net>
Date: 2012-01-24 21:57:16
Also in:
lkml
On Tue, 17 Jan 2012 20:51:13 +0200 (EET) Pekka Enberg [off-list ref] wrote:
Ok, so here's a proof of concept patch that implements sample-base per-process free threshold VM event watching using perf-like syscall ABI. I'd really like to see something like this that's much more extensible and clean than the /dev based ABIs that people have proposed so far.
OK, so I'm slow, but better late than never. I plead travel. I guess the thing that surprises me is that nobody has said this yet: this looks a lot like an event-reporting mechanism like perf. Is there a reason these can't be perf-style events integrated with all the rest?
+struct vmnotify_config {
+ /*
+ * Size of the struct for ABI extensibility.
+ */
+ __u32 size;
+
+ /*
+ * Notification type bitmask
+ */
+ __u64 type;
+
+ /*
+ * Free memory threshold in percentages [1..99]
+ */
+ __u32 free_threshold;Is this an upper-bound threshold or a lower-bound threshold? From your example, it looks like "free_threshold" is "the amount of memory that is not free", which seems confusing. [...]
quoted hunk ↗ jump to hunk
new file mode 100644 index 0000000..6800450--- /dev/null +++ b/mm/vmnotify.c@@ -0,0 +1,235 @@ +#include <linux/anon_inodes.h> +#include <linux/vmnotify.h> +#include <linux/syscalls.h> +#include <linux/file.h> +#include <linux/list.h> +#include <linux/poll.h> +#include <linux/slab.h> +#include <linux/swap.h> + +#define VMNOTIFY_MAX_FREE_THRESHOD 100
Did we run out of L's here? :)
+static ssize_t vmnotify_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
+{
+ struct vmnotify_watch *watch = file->private_data;
+ int ret = 0;
+
+ mutex_lock(&watch->mutex);
+
+ if (!watch->pending)
+ goto out_unlock;
+
+ if (copy_to_user(buf, &watch->event, sizeof(struct vmnotify_event))) {
+ ret = -EFAULT;
+ goto out_unlock;
+ }
+
+ ret = watch->event.size;
+
+ watch->pending = false;
+
+out_unlock:
+ mutex_unlock(&watch->mutex);
+
+ return ret;
+}So this is a nonblocking-only interface? That may surprise some developers. You already have a wait queue, why not wait on it if need be?
+static int vmnotify_copy_config(struct vmnotify_config __user *uconfig,
+ struct vmnotify_config *config)
+{
+ int ret;
+
+ ret = copy_from_user(config, uconfig, sizeof(struct vmnotify_config));
+ if (ret)
+ return -EFAULT;
+
+ if (!config->type)
+ return -EINVAL;
+
+ if (config->type & VMNOTIFY_TYPE_SAMPLE) {
+ if (config->sample_period_ns < NSEC_PER_MSEC)
+ return -EINVAL;
+ }What happens if the sample period is zero? jon -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>