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    SubjectRe: [PATCH 3/12] ksm: pages_unshared and pages_volatile
    Hugh Dickins wrote:
    > The pages_shared and pages_sharing counts give a good picture of how
    > successful KSM is at sharing; but no clue to how much wasted work it's
    > doing to get there. Add pages_unshared (count of unique pages waiting
    > in the unstable tree, hoping to find a mate) and pages_volatile.
    >
    > pages_volatile is harder to define. It includes those pages changing
    > too fast to get into the unstable tree, but also whatever other edge
    > conditions prevent a page getting into the trees: a high value may
    > deserve investigation. Don't try to calculate it from the various
    > conditions: it's the total of rmap_items less those accounted for.
    >
    > Also show full_scans: the number of completed scans of everything
    > registered in the mm list.
    >
    > The locking for all these counts is simply ksm_thread_mutex.
    >
    > Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
    > ---
    >
    > mm/ksm.c | 52 +++++++++++++++++++++++++++++++++++++++++++++++++++-
    > 1 file changed, 51 insertions(+), 1 deletion(-)
    >
    > --- ksm2/mm/ksm.c 2009-08-02 13:49:43.000000000 +0100
    > +++ ksm3/mm/ksm.c 2009-08-02 13:49:51.000000000 +0100
    > @@ -155,6 +155,12 @@ static unsigned long ksm_pages_shared;
    > /* The number of page slots additionally sharing those nodes */
    > static unsigned long ksm_pages_sharing;
    >
    > +/* The number of nodes in the unstable tree */
    > +static unsigned long ksm_pages_unshared;
    > +
    > +/* The number of rmap_items in use: to calculate pages_volatile */
    > +static unsigned long ksm_rmap_items;
    > +
    > /* Limit on the number of unswappable pages used */
    > static unsigned long ksm_max_kernel_pages;
    >
    > @@ -204,11 +210,17 @@ static void __init ksm_slab_free(void)
    >
    > static inline struct rmap_item *alloc_rmap_item(void)
    > {
    > - return kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL);
    > + struct rmap_item *rmap_item;
    > +
    > + rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL);
    > + if (rmap_item)
    > + ksm_rmap_items++;
    > + return rmap_item;
    > }
    >
    > static inline void free_rmap_item(struct rmap_item *rmap_item)
    > {
    > + ksm_rmap_items--;
    > rmap_item->mm = NULL; /* debug safety */
    > kmem_cache_free(rmap_item_cache, rmap_item);
    > }
    > @@ -419,6 +431,7 @@ static void remove_rmap_item_from_tree(s
    > BUG_ON(age > 2);
    > if (!age)
    > rb_erase(&rmap_item->node, &root_unstable_tree);
    > + ksm_pages_unshared--;
    > }
    >
    > rmap_item->address &= PAGE_MASK;
    > @@ -1002,6 +1015,7 @@ static struct rmap_item *unstable_tree_s
    > rb_link_node(&rmap_item->node, parent, new);
    > rb_insert_color(&rmap_item->node, &root_unstable_tree);
    >
    > + ksm_pages_unshared++;
    > return NULL;
    > }
    >
    > @@ -1098,6 +1112,8 @@ static void cmp_and_merge_page(struct pa
    > if (!err) {
    > rb_erase(&tree_rmap_item->node, &root_unstable_tree);
    > tree_rmap_item->address &= ~NODE_FLAG;
    > + ksm_pages_unshared--;
    > +
    > /*
    > * If we fail to insert the page into the stable tree,
    > * we will have 2 virtual addresses that are pointing
    > @@ -1481,6 +1497,37 @@ static ssize_t pages_sharing_show(struct
    > }
    > KSM_ATTR_RO(pages_sharing);
    >
    > +static ssize_t pages_unshared_show(struct kobject *kobj,
    > + struct kobj_attribute *attr, char *buf)
    > +{
    > + return sprintf(buf, "%lu\n", ksm_pages_unshared);
    > +}
    > +KSM_ATTR_RO(pages_unshared);
    > +
    > +static ssize_t pages_volatile_show(struct kobject *kobj,
    > + struct kobj_attribute *attr, char *buf)
    > +{
    > + long ksm_pages_volatile;
    > +
    > + ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
    > + - ksm_pages_sharing - ksm_pages_unshared;
    > + /*
    > + * It was not worth any locking to calculate that statistic,
    > + * but it might therefore sometimes be negative: conceal that.
    > + */
    > + if (ksm_pages_volatile < 0)
    > + ksm_pages_volatile = 0;
    > + return sprintf(buf, "%ld\n", ksm_pages_volatile);

    ACK.


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