On Fri, Dec 02, 2011 at 06:40:27PM +0800, Bob Liu wrote:
> There are multi places need to get swap_cgroup, so add a helper
> function:
> static struct swap_cgroup *swap_cgroup_getsc(swp_entry_t ent,
> struct swap_cgroup_ctrl **ctrl);
> to simple the code.
>
> v1 -> v2:
> - add parameter struct swap_cgroup_ctrl **ctrl suggested by Michal
>
> Signed-off-by: Bob Liu <lliubbo@xxxxxxxxx>
> ---
> mm/page_cgroup.c | 57 ++++++++++++++++++++++-------------------------------
> 1 files changed, 24 insertions(+), 33 deletions(-)
>
> diff --git a/mm/page_cgroup.c b/mm/page_cgroup.c
> index f0559e0..1970e8a 100644
> --- a/mm/page_cgroup.c
> +++ b/mm/page_cgroup.c
> @@ -362,6 +362,27 @@ not_enough_page:
> return -ENOMEM;
> }
I realize that you mostly moved what was already there, but there are
a couple more things to clean up. Would you like to send a patch for
them as well?
> +static struct swap_cgroup *swap_cgroup_getsc(swp_entry_t ent,
> + struct swap_cgroup_ctrl **ctrl)
__lookup_swap_cgroup()? Or even more matching names would be to have
that public interface called lookup_swap_cgroup_id() and let this one
be lookup_swap_cgroup().
> +{
> + int type = swp_type(ent);
swp_type() returns unsigned int
> + unsigned long offset = swp_offset(ent);
swp_offset() returns pgoff_t
> + unsigned long idx = offset / SC_PER_PAGE;
> + unsigned long pos = offset & SC_POS_MASK;
This is actually quite crappy, the definition looks like this:
#define SC_PER_PAGE (PAGE_SIZE/sizeof(struct swap_cgroup))
#define SC_POS_MASK (SC_PER_PAGE - 1)
which relies on the fact that the division named SC_PER_PAGE yields a
power of two, which only is true by accident.
Better would be to delete SC_POS_MASK and use offset % SC_PER_PAGE
instead.
> + struct swap_cgroup_ctrl *temp_ctrl;
> + struct page *mappage;
> + struct swap_cgroup *sc;
> +
> + temp_ctrl = &swap_cgroup_ctrl[type];
> + if (ctrl)
> + *ctrl = temp_ctrl;
Name the output parameter ctrlp instead? Then you can call the local
one ctrl.
Also, type is only used once, better to just inline it:
&swap_cgroup_ctrl[swp_type(ent)]
> + mappage = temp_ctrl->map[idx];
Same for idx, just use ctrl->map[offset / SC_PER_PAGE] directly.
> + sc = page_address(mappage);
> + sc += pos;
> + return sc;
> +}
That seems elaborate.
return page_address(mappage) + offset % SC_PER_PAGE
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