On Thu, Mar 17, 2016 at 08:09:50PM +0800, YiPing Xu wrote:
>
>
> On 2016/3/15 14:51, Minchan Kim wrote:
> >On Tue, Mar 15, 2016 at 03:40:53PM +0900, Sergey Senozhatsky wrote:
> >>On (03/11/16 16:30), Minchan Kim wrote:
> >>>-static void *location_to_obj(struct page *page, unsigned long obj_idx)
> >>>+static void objidx_to_page_and_ofs(struct size_class *class,
> >>>+ struct page *first_page,
> >>>+ unsigned long obj_idx,
> >>>+ struct page **obj_page,
> >>>+ unsigned long *ofs_in_page)
> >>
> >>this looks big; 5 params, function "returning" both page and offset...
> >>any chance to split it in two steps, perhaps?
> >
> >Yes, it's rather ugly but I don't have a good idea.
> >Feel free to suggest if you have a better idea.
> >
> >>
> >>besides, it is more intuitive (at least to me) when 'offset'
> >>shortened to 'offt', not 'ofs'.
>
> the purpose to get 'obj_page' and 'ofs_in_page' is to map the page
> and get the meta-data pointer in the page, so, we can finish this in
> a single function.
>
> just like this, and maybe we could have a better function name
>
> static unsigned long *map_handle(struct size_class *class,
> struct page *first_page, unsigned long obj_idx)
> {
> struct page *cursor = first_page;
> unsigned long offset = obj_idx * class->size;
> int nr_page = offset >> PAGE_SHIFT;
> unsigned long offset_in_page = offset & ~PAGE_MASK;
> void *addr;
> int i;
>
> if (class->huge) {
> VM_BUG_ON_PAGE(!is_first_page(page), page);
> return &page_private(page);
> }
>
> for (i = 0; i < nr_page; i++)
> cursor = get_next_page(cursor);
>
> addr = kmap_atomic(cursor);
>
> return addr + offset_in_page;
> }
>
> static void unmap_handle(unsigned long *addr)
> {
> if (class->huge) {
> return;
> }
>
> kunmap_atomic(addr & ~PAGE_MASK);
> }
>
> all functions called "objidx_to_page_and_ofs" could use it like
> this, for example:
>
> static unsigned long handle_from_obj(struct size_class *class,
> struct page *first_page, int obj_idx)
> {
> unsigned long *head = map_handle(class, first_page, obj_idx);
>
> if (*head & OBJ_ALLOCATED_TAG)
> handle = *head & ~OBJ_ALLOCATED_TAG;
>
> unmap_handle(*head);
>
> return handle;
> }
>
> 'freeze_zspage', u'nfreeze_zspage' use it in the same way.
>
> but in 'obj_malloc', we still have to get the page to get obj.
>
> obj = location_to_obj(m_page, obj);
Yes, That's why I didn't use such pattern. I didn't want to
add unnecessary overhead in that hot path.
