On Wed, Jun 01, 2016 at 04:09:26PM +0200, Vlastimil Babka wrote:
> On 06/01/2016 01:21 AM, Minchan Kim wrote:
>
> [...]
>
> >
> > Cc: Sergey Senozhatsky <sergey.senozhat...@gmail.com>
> > Signed-off-by: Minchan Kim <minc...@kernel.org>
>
> I'm not that familiar with zsmalloc, so this is not a full review. I was
> just curious how it's handling the movable migration API, and stumbled
> upon some things pointed out below.
>
> > @@ -252,16 +276,23 @@ struct zs_pool {
> > */
> > #define FULLNESS_BITS 2
> > #define CLASS_BITS 8
> > +#define ISOLATED_BITS 3
> > +#define MAGIC_VAL_BITS 8
> >
> > struct zspage {
> > struct {
> > unsigned int fullness:FULLNESS_BITS;
> > unsigned int class:CLASS_BITS;
> > + unsigned int isolated:ISOLATED_BITS;
> > + unsigned int magic:MAGIC_VAL_BITS;
>
> This magic seems to be only tested via VM_BUG_ON, so it's presence
> should be also guarded by #ifdef DEBUG_VM, no?
Thanks for the point.
Then, I want to change it to BUG_ON because struct zspage corruption
is really risky to work rightly and want to catch on it in real product
which disable CONFIG_DEBUG_VM for a while until make the feature stable.
>
> > @@ -999,6 +1141,8 @@ static struct zspage *alloc_zspage(struct zs_pool
> > *pool,
> > return NULL;
> >
> > memset(zspage, 0, sizeof(struct zspage));
> > + zspage->magic = ZSPAGE_MAGIC;
>
> Same here.
>
> > +int zs_page_migrate(struct address_space *mapping, struct page *newpage,
> > + struct page *page, enum migrate_mode mode)
> > +{
> > + struct zs_pool *pool;
> > + struct size_class *class;
> > + int class_idx;
> > + enum fullness_group fullness;
> > + struct zspage *zspage;
> > + struct page *dummy;
> > + void *s_addr, *d_addr, *addr;
> > + int offset, pos;
> > + unsigned long handle, head;
> > + unsigned long old_obj, new_obj;
> > + unsigned int obj_idx;
> > + int ret = -EAGAIN;
> > +
> > + VM_BUG_ON_PAGE(!PageMovable(page), page);
> > + VM_BUG_ON_PAGE(!PageIsolated(page), page);
> > +
> > + zspage = get_zspage(page);
> > +
> > + /* Concurrent compactor cannot migrate any subpage in zspage */
> > + migrate_write_lock(zspage);
> > + get_zspage_mapping(zspage, &class_idx, &fullness);
> > + pool = mapping->private_data;
> > + class = pool->size_class[class_idx];
> > + offset = get_first_obj_offset(class, get_first_page(zspage), page);
> > +
> > + spin_lock(&class->lock);
> > + if (!get_zspage_inuse(zspage)) {
> > + ret = -EBUSY;
> > + goto unlock_class;
> > + }
> > +
> > + pos = offset;
> > + s_addr = kmap_atomic(page);
> > + while (pos < PAGE_SIZE) {
> > + head = obj_to_head(page, s_addr + pos);
> > + if (head & OBJ_ALLOCATED_TAG) {
> > + handle = head & ~OBJ_ALLOCATED_TAG;
> > + if (!trypin_tag(handle))
> > + goto unpin_objects;
> > + }
> > + pos += class->size;
> > + }
> > +
> > + /*
> > + * Here, any user cannot access all objects in the zspage so let's move.
> > + */
> > + d_addr = kmap_atomic(newpage);
> > + memcpy(d_addr, s_addr, PAGE_SIZE);
> > + kunmap_atomic(d_addr);
> > +
> > + for (addr = s_addr + offset; addr < s_addr + pos;
> > + addr += class->size) {
> > + head = obj_to_head(page, addr);
> > + if (head & OBJ_ALLOCATED_TAG) {
> > + handle = head & ~OBJ_ALLOCATED_TAG;
> > + if (!testpin_tag(handle))
> > + BUG();
> > +
> > + old_obj = handle_to_obj(handle);
> > + obj_to_location(old_obj, &dummy, &obj_idx);
> > + new_obj = (unsigned long)location_to_obj(newpage,
> > + obj_idx);
> > + new_obj |= BIT(HANDLE_PIN_BIT);
> > + record_obj(handle, new_obj);
> > + }
> > + }
> > +
> > + replace_sub_page(class, zspage, newpage, page);
> > + get_page(newpage);
> > +
> > + dec_zspage_isolation(zspage);
> > +
> > + /*
> > + * Page migration is done so let's putback isolated zspage to
> > + * the list if @page is final isolated subpage in the zspage.
> > + */
> > + if (!is_zspage_isolated(zspage))
> > + putback_zspage(class, zspage);
> > +
> > + reset_page(page);
> > + put_page(page);
> > + page = newpage;
> > +
> > + ret = 0;
> > +unpin_objects:
> > + for (addr = s_addr + offset; addr < s_addr + pos;
> > + addr += class->size) {
> > + head = obj_to_head(page, addr);
> > + if (head & OBJ_ALLOCATED_TAG) {
> > + handle = head & ~OBJ_ALLOCATED_TAG;
> > + if (!testpin_tag(handle))
> > + BUG();
> > + unpin_tag(handle);
> > + }
> > + }
> > + kunmap_atomic(s_addr);
>
> The above seems suspicious to me. In the success case, page points to
> newpage, but s_addr is still the original one?
s_addr is virtual adress of old page by kmap_atomic so page pointer of
new page doesn't matter.
>
> Vlastimil
>
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majord...@kvack.org. For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"d...@kvack.org";> em...@kvack.org </a>
