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    Subject[RFC 19/43] mm: PKRAM: allow preserved memory to be freed from userspace
    Date
    To free all space utilized for preserved memory, one can write 0 to
    /sys/kernel/pkram. This will destroy all PKRAM nodes that are not
    currently being read or written.

    Originally-by: Vladimir Davydov <vdavydov.dev@gmail.com>
    Signed-off-by: Anthony Yznaga <anthony.yznaga@oracle.com>
    ---
    mm/pkram.c | 39 ++++++++++++++++++++++++++++++++++++++-
    1 file changed, 38 insertions(+), 1 deletion(-)

    diff --git a/mm/pkram.c b/mm/pkram.c
    index 0aaaf9b79682..95e691382721 100644
    --- a/mm/pkram.c
    +++ b/mm/pkram.c
    @@ -509,6 +509,32 @@ static void pkram_truncate_node(struct pkram_node *node)
    node->obj_pfn = 0;
    }

    +/*
    + * Free all nodes that are not under operation.
    + */
    +static void pkram_truncate(void)
    +{
    + struct page *page, *tmp;
    + struct pkram_node *node;
    + LIST_HEAD(dispose);
    +
    + mutex_lock(&pkram_mutex);
    + list_for_each_entry_safe(page, tmp, &pkram_nodes, lru) {
    + node = page_address(page);
    + if (!(node->flags & PKRAM_ACCMODE_MASK))
    + list_move(&page->lru, &dispose);
    + }
    + mutex_unlock(&pkram_mutex);
    +
    + while (!list_empty(&dispose)) {
    + page = list_first_entry(&dispose, struct page, lru);
    + list_del(&page->lru);
    + node = page_address(page);
    + pkram_truncate_node(node);
    + pkram_free_page(node);
    + }
    +}
    +
    static void pkram_add_link(struct pkram_link *link, struct pkram_obj *obj)
    {
    link->link_pfn = obj->link_pfn;
    @@ -1141,8 +1167,19 @@ static ssize_t show_pkram_sb_pfn(struct kobject *kobj,
    return sprintf(buf, "%lx\n", pfn);
    }

    +static ssize_t store_pkram_sb_pfn(struct kobject *kobj,
    + struct kobj_attribute *attr, const char *buf, size_t count)
    +{
    + int val;
    +
    + if (kstrtoint(buf, 0, &val) || val)
    + return -EINVAL;
    + pkram_truncate();
    + return count;
    +}
    +
    static struct kobj_attribute pkram_sb_pfn_attr =
    - __ATTR(pkram, 0444, show_pkram_sb_pfn, NULL);
    + __ATTR(pkram, 0644, show_pkram_sb_pfn, store_pkram_sb_pfn);

    static struct attribute *pkram_attrs[] = {
    &pkram_sb_pfn_attr.attr,
    --
    2.13.3
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