Messages in this thread | | | Date | Tue, 24 Jan 2012 14:57:13 -0700 | From | Jonathan Corbet <> | Subject | Re: [RFC 1/3] /dev/low_mem_notify |
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On Tue, 17 Jan 2012 20:51:13 +0200 (EET) Pekka Enberg <penberg@kernel.org> 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.
[...]
> 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
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