On Wednesday 18 January 2012, Pekka Enberg wrote:

quoted

quoted

+struct vmnotify_event {
+     /* Size of the struct for ABI extensibility. */
+     __u32                   size;
+
+     __u64                   nr_avail_pages;
+
+     __u64                   nr_swap_pages;
+
+     __u64                   nr_free_pages;
+};

Two fields here most likely session-constant, (nr_avail_pages and
nr_swap_pages), seems not much sense to report them in every event.  If we
have memory/swap hotplug user-space can use sysinfo() call.

I actually changed the ABI to look like this:

struct vmnotify_event {
        /*
         * Size of the struct for ABI extensibility.
         */
        __u32                   size;

        __u64                   attrs;

        __u64                   attr_values[];
};

So userspace can decide which fields to include in notifications.

Please make the first member a __u64 instead of a __u32. This will
avoid incompatibility between 32 and 64 bit processes, which have
different alignment rules on x86: x86-32 would implicitly pack the
struct while x86-64 would add padding with your layout.

	Arnd

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