On Mon, 28 Feb 2011 00:49:25 +0900
Minchan Kim <minchan.kim@xxxxxxxxx> wrote:
> This patch cleans up unncessary BUG_ON check and confusing
> charge variable.
>
> That's because memcg charge/uncharge could be handled by
> mem_cgroup_[prepare/end] migration itself so charge local variable
> in unmap_and_move lost the role since we introduced 01b1ae63c2.
>
> And mem_cgroup_prepare_migratio return 0 if only it is successful.
> Otherwise, it jumps to unlock label to clean up so BUG_ON(charge)
> isn;t meaningless.
>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx>
> Cc: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> Signed-off-by: Minchan Kim <minchan.kim@xxxxxxxxx>
It looks good to me, but I have one minor comment.
> ---
> mm/memcontrol.c | 1 +
> mm/migrate.c | 14 ++++----------
> 2 files changed, 5 insertions(+), 10 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 2fc97fc..6832926 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2872,6 +2872,7 @@ static inline int mem_cgroup_move_swap_account(swp_entry_t entry,
> /*
> * Before starting migration, account PAGE_SIZE to mem_cgroup that the old
> * page belongs to.
> + * Return 0 if charge is successful. Otherwise return -errno.
> */
> int mem_cgroup_prepare_migration(struct page *page,
> struct page *newpage, struct mem_cgroup **ptr, gfp_t gfp_mask)
> diff --git a/mm/migrate.c b/mm/migrate.c
> index eb083a6..737c2e5 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -622,7 +622,6 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
> int *result = NULL;
> struct page *newpage = get_new_page(page, private, &result);
> int remap_swapcache = 1;
> - int charge = 0;
> struct mem_cgroup *mem;
> struct anon_vma *anon_vma = NULL;
>
> @@ -637,9 +636,7 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
> if (unlikely(split_huge_page(page)))
> goto move_newpage;
>
> - /* prepare cgroup just returns 0 or -ENOMEM */
> rc = -EAGAIN;
> -
> if (!trylock_page(page)) {
> if (!force)
> goto move_newpage;
> @@ -678,13 +675,11 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
> }
>
> /* charge against new page */
> - charge = mem_cgroup_prepare_migration(page, newpage, &mem, GFP_KERNEL);
> - if (charge == -ENOMEM) {
> - rc = -ENOMEM;
> + rc = mem_cgroup_prepare_migration(page, newpage, &mem, GFP_KERNEL);
> + if (rc)
> goto unlock;
> - }
> - BUG_ON(charge);
>
> + rc = -EAGAIN;
> if (PageWriteback(page)) {
> if (!force || !sync)
> goto uncharge;
How about
if (mem_cgroup_prepare_migration(..)) {
rc = -ENOMEM;
goto unlock;
}
?
Re-setting "rc" to -EAGAIN is not necessary in this case.
"if (mem_cgroup_...)" is commonly used in many places.
Anyway,
Acked-by: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx>
Thanks,
Daisuke Nishimura.
> @@ -767,8 +762,7 @@ skip_unmap:
> drop_anon_vma(anon_vma);
>
> uncharge:
> - if (!charge)
> - mem_cgroup_end_migration(mem, page, newpage, rc == 0);
> + mem_cgroup_end_migration(mem, page, newpage, rc == 0);
> unlock:
> unlock_page(page);
>
> --
> 1.7.1
>
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