Messages in this thread | | | Date | Mon, 4 May 2009 22:08:06 +0530 | From | Balbir Singh <> | Subject | Re: [PATCH] memcg: fix stale swap cache leak v5 |
| |
* Daisuke Nishimura <d-nishimura@mtf.biglobe.ne.jp> [2009-05-01 13:33:17]:
> processA | processB > -------------------------------------+------------------------------------- > (page_remove_rmap()) | (shrink_page_list()) > mem_cgroup_uncharge_page() | > ->uncharged because it's not | > PageSwapCache yet. | > So, both mem/memsw.usage | > are decremented. | > | add_to_swap() -> added to swap cache. > > If this page goes thorough without being freed for some reason, this page > doesn't goes back to memcg's LRU because of !PageCgroupUsed.
For some reason could use some clarification.
> > These swap cache cannot be freed in memcg's LRU scanning, and swp_entry cannot > be freed properly as a result. > This patch adds a hook after add_to_swap() to check the page is mapped by a > process or not, and frees it if it has been unmapped already. > > If a page has been on swap cache already when the owner process calls > page_remove_rmap() -> mem_cgroup_uncharge_page(), the page is not uncharged. > It goes back to memcg's LRU even if it goes through shrink_page_list() > without being freed, so this patch ignores these case. > > Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> > --- > include/linux/swap.h | 12 ++++++++++++ > mm/memcontrol.c | 14 ++++++++++++++ > mm/vmscan.c | 8 ++++++++ > 3 files changed, 34 insertions(+), 0 deletions(-) > > diff --git a/include/linux/swap.h b/include/linux/swap.h > index caf0767..8e75d7a 100644 > --- a/include/linux/swap.h > +++ b/include/linux/swap.h > @@ -336,11 +336,17 @@ static inline void disable_swap_token(void) > > #ifdef CONFIG_CGROUP_MEM_RES_CTLR > extern void mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent); > +extern int memcg_free_unused_swapcache(struct page *page); > #else > static inline void > mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent) > { > } > +static inline int > +memcg_free_unused_swapcache(struct page *page) > +{ > + return 0; > +} > #endif > #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP > extern void mem_cgroup_uncharge_swap(swp_entry_t ent); > @@ -431,6 +437,12 @@ static inline swp_entry_t get_swap_page(void) > #define has_swap_token(x) 0 > #define disable_swap_token() do { } while(0) > > +static inline int > +memcg_free_unused_swapcache(struct page *page) > +{ > + return 0; > +} > + > #endif /* CONFIG_SWAP */ > #endif /* __KERNEL__*/ > #endif /* _LINUX_SWAP_H */ > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 01c2d8f..4f7e5b6 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -1488,6 +1488,7 @@ void mem_cgroup_uncharge_cache_page(struct page *page) > __mem_cgroup_uncharge_common(page, MEM_CGROUP_CHARGE_TYPE_CACHE); > } > > +#ifdef CONFIG_SWAP > /* > * called from __delete_from_swap_cache() and drop "page" account. > * memcg information is recorded to swap_cgroup of "ent" > @@ -1507,6 +1508,19 @@ void mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent) > css_put(&memcg->css); > } > > +int memcg_free_unused_swapcache(struct page *page) > +{ > + VM_BUG_ON(!PageLocked(page)); > + VM_BUG_ON(!PageSwapCache(page)); > + > + if (mem_cgroup_disabled()) > + return 0; > + if (!PageAnon(page) || page_mapped(page)) > + return 0;
Do we need these checks? Isn't PageSwapCache() check and page_swapcount() check enough in try_to_free_swap()?
> + return try_to_free_swap(page); /* checks page_swapcount */
try_to_free_swap() marks the page as dirty, do you know why?
> +} > +#endif /* CONFIG_SWAP */ > + > #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP > /* > * called from swap_entry_free(). remove record in swap_cgroup and > diff --git a/mm/vmscan.c b/mm/vmscan.c > index eac9577..c1a7a6f 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -656,6 +656,14 @@ static unsigned long shrink_page_list(struct list_head *page_list, > goto keep_locked; > if (!add_to_swap(page)) > goto activate_locked; > + /* > + * The owner process might have uncharged the page > + * (by page_remove_rmap()) before it has been added > + * to swap cache. > + * Check it here to avoid making it stale. > + */ > + if (memcg_free_unused_swapcache(page)) > + goto keep_locked;
Seems reasonable, but I think it is better to check for scan_global_lru().. no?
> may_enter_fs = 1; > } > >
-- Balbir
| |