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SubjectRe: [patch 04/11] mm: memcg: push down PageSwapCache check into uncharge entry functions
(2012/07/05 9:44), Johannes Weiner wrote:
> Not all uncharge paths need to check if the page is swapcache, some of
> them can know for sure.
>
> Push down the check into all callsites of uncharge_common() so that
> the patch that removes some of them is more obvious.
>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
> ---

some nitpick.

> mm/memcontrol.c | 18 ++++++++++++------
> 1 files changed, 12 insertions(+), 6 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 4ea19c6..a3bf414 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2920,8 +2920,7 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype,
> if (mem_cgroup_disabled())
> return NULL;
>
> - if (PageSwapCache(page))
> - return NULL;
> + VM_BUG_ON(PageSwapCache(page));
>
> if (PageTransHuge(page)) {
> nr_pages <<= compound_order(page);
> @@ -3018,6 +3017,8 @@ void mem_cgroup_uncharge_page(struct page *page)
> if (page_mapped(page))
> return;
> VM_BUG_ON(page->mapping && !PageAnon(page));
> + if (PageSwapCache(page))
> + return;
> __mem_cgroup_uncharge_common(page, MEM_CGROUP_CHARGE_TYPE_ANON, false);
> }
>
> @@ -3025,6 +3026,8 @@ void mem_cgroup_uncharge_cache_page(struct page *page)
> {
> VM_BUG_ON(page_mapped(page));
> VM_BUG_ON(page->mapping);
> + if (PageSwapCache(page))
> + return;
> __mem_cgroup_uncharge_common(page, MEM_CGROUP_CHARGE_TYPE_CACHE, false);
> }
>
> @@ -3089,6 +3092,8 @@ mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent, bool swapout)
> if (!swapout) /* this was a swap cache but the swap is unused ! */
> ctype = MEM_CGROUP_CHARGE_TYPE_DROP;
>
> + if (PageSwapCache(page))
> + return;
> memcg = __mem_cgroup_uncharge_common(page, ctype, false);
>
> /*
> @@ -3278,10 +3283,11 @@ void mem_cgroup_end_migration(struct mem_cgroup *memcg,
> unused = oldpage;
> }
> anon = PageAnon(used);
> - __mem_cgroup_uncharge_common(unused,
> - anon ? MEM_CGROUP_CHARGE_TYPE_ANON
> - : MEM_CGROUP_CHARGE_TYPE_CACHE,
> - true);
> + if (!PageSwapCache(page))
> + __mem_cgroup_uncharge_common(unused,
> + anon ? MEM_CGROUP_CHARGE_TYPE_ANON
> + : MEM_CGROUP_CHARGE_TYPE_CACHE,
> + true);

!PageSwapCache(unused) ?

But I think unused page's PG_swapcache is always dropped. So, the check is
not necessary.

Thanks,
-Kame












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