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Date: Mon, 13 May 2013 16:58:57 +0200
From: Michal Hocko <mhocko@...e.cz>
To: Minchan Kim <minchan@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, Rik van Riel <riel@...hat.com>,
Mel Gorman <mgorman@...e.de>,
Johannes Weiner <hannes@...xchg.org>,
Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
Hugh Dickins <hughd@...gle.com>
Subject: Re: [RFC 3/4] mm: support remove_mapping in irqcontext
On Mon 13-05-13 11:10:47, Minchan Kim wrote:
[...]
> My rough plan is following as,
>
> 1. Make mctz->lock beging aware of irq by changing spin_lock with
> spin_lock_irqsave.
I wouldn't be worried about this one as it is on its way out with the
soft limit rework (the core uncontroversial part ;))
> 2. Introuduce new argument "locked" in __mem_cgroup_uncharge_common
> so that __mem_cgroup_uncharge_common can avoid lock_page_cgroup in
> irqcontext to avoid deadlock but caller in irqcontext should be held
> it in advance by next patch.
> 3. Introduce try_lock_page_cgroup, which will be used __swapcache_free.
> 4. __remove_mapping can held a page_cgroup lock in advance before calling
> __swapcache_free
>
> I'd like to listen memcg people's opinions before diving into coding.
It should work. It will require some code moving, though.
> Signed-off-by: Minchan Kim <minchan@...nel.org>
> ---
> fs/splice.c | 2 +-
> include/linux/swap.h | 12 ++++++++++-
> mm/swapfile.c | 2 +-
> mm/truncate.c | 2 +-
> mm/vmscan.c | 56 +++++++++++++++++++++++++++++++++++++++++++---------
> 5 files changed, 61 insertions(+), 13 deletions(-)
>
> diff --git a/fs/splice.c b/fs/splice.c
> index e6b2559..db77694 100644
> --- a/fs/splice.c
> +++ b/fs/splice.c
> @@ -70,7 +70,7 @@ static int page_cache_pipe_buf_steal(struct pipe_inode_info *pipe,
> * If we succeeded in removing the mapping, set LRU flag
> * and return good.
> */
> - if (remove_mapping(mapping, page)) {
> + if (remove_mapping(mapping, page, false)) {
> buf->flags |= PIPE_BUF_FLAG_LRU;
> return 0;
> }
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index ca031f7..eb126d2 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -274,7 +274,8 @@ extern unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *mem,
> unsigned long *nr_scanned);
> extern unsigned long shrink_all_memory(unsigned long nr_pages);
> extern int vm_swappiness;
> -extern int remove_mapping(struct address_space *mapping, struct page *page);
> +extern int remove_mapping(struct address_space *mapping, struct page *page,
> + bool irqcontext);
> extern unsigned long vm_total_pages;
>
> #ifdef CONFIG_NUMA
> @@ -407,6 +408,9 @@ mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent, bool swapout)
> }
> #endif
>
> +
> +extern struct swap_info_struct *swap_info_get(swp_entry_t entry);
> +
> #else /* CONFIG_SWAP */
>
> #define get_nr_swap_pages() 0L
> @@ -430,6 +434,12 @@ static inline void show_swap_cache_info(void)
> #define free_swap_and_cache(swp) is_migration_entry(swp)
> #define swapcache_prepare(swp) is_migration_entry(swp)
>
> +
> +struct swap_info_struct *swap_info_get(swp_entry_t entry)
> +{
> + return NULL;
> +}
> +
> static inline int add_swap_count_continuation(swp_entry_t swp, gfp_t gfp_mask)
> {
> return 0;
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 33ebdd5..8a425d4 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -505,7 +505,7 @@ swp_entry_t get_swap_page_of_type(int type)
> return (swp_entry_t) {0};
> }
>
> -static struct swap_info_struct *swap_info_get(swp_entry_t entry)
> +struct swap_info_struct *swap_info_get(swp_entry_t entry)
> {
> struct swap_info_struct *p;
> unsigned long offset, type;
> diff --git a/mm/truncate.c b/mm/truncate.c
> index c75b736..fa1dc60 100644
> --- a/mm/truncate.c
> +++ b/mm/truncate.c
> @@ -131,7 +131,7 @@ invalidate_complete_page(struct address_space *mapping, struct page *page)
> if (page_has_private(page) && !try_to_release_page(page, 0))
> return 0;
>
> - ret = remove_mapping(mapping, page);
> + ret = remove_mapping(mapping, page, false);
>
> return ret;
> }
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index fa6a853..d14c9be 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -450,12 +450,18 @@ static pageout_t pageout(struct page *page, struct address_space *mapping,
> * Same as remove_mapping, but if the page is removed from the mapping, it
> * gets returned with a refcount of 0.
> */
> -static int __remove_mapping(struct address_space *mapping, struct page *page)
> +static int __remove_mapping(struct address_space *mapping, struct page *page,
> + bool irqcontext)
> {
> + unsigned long flags;
> +
> BUG_ON(!PageLocked(page));
> BUG_ON(mapping != page_mapping(page));
>
> - spin_lock_irq(&mapping->tree_lock);
> + if (irqcontext)
> + spin_lock_irqsave(&mapping->tree_lock, flags);
> + else
> + spin_lock_irq(&mapping->tree_lock);
> /*
> * The non racy check for a busy page.
> *
> @@ -490,17 +496,45 @@ static int __remove_mapping(struct address_space *mapping, struct page *page)
> }
>
> if (PageSwapCache(page)) {
> + struct swap_info_struct *p;
> swp_entry_t swap = { .val = page_private(page) };
> + p = swap_info_get(swap);
> + /*
> + * If we are irq context, check that we can get a
> + * swap_info_strcut->lock before removing the page from
> + * swap cache. Because __swapcache_free must be successful.
> + * If __swapcache_free can be failed, we should rollback
> + * things done by __delete_from_swap_cache and it needs
> + * memory allocation for radix tree node in irqcontext
> + * That's thing we really want to avoid.
> + * TODO : memcg mem_cgroup_uncharge_swapcache handling
> + * in irqcontext
> + */
> + if (irqcontext && p && !spin_trylock(&p->lock)) {
> + page_unfreeze_refs(page, 2);
> + goto cannot_free;
> + }
> +
> __delete_from_swap_cache(page);
> - spin_unlock_irq(&mapping->tree_lock);
> - swapcache_free(swap, page);
> + if (irqcontext) {
> + spin_unlock_irqrestore(&mapping->tree_lock, flags);
> + if (p)
> + __swapcache_free(p, swap, page);
> + spin_unlock(&p->lock);
> + } else {
> + spin_unlock_irq(&mapping->tree_lock);
> + swapcache_free(swap, page);
> + }
> } else {
> void (*freepage)(struct page *);
>
> freepage = mapping->a_ops->freepage;
>
> __delete_from_page_cache(page);
> - spin_unlock_irq(&mapping->tree_lock);
> + if (irqcontext)
> + spin_unlock_irqrestore(&mapping->tree_lock, flags);
> + else
> + spin_unlock_irq(&mapping->tree_lock);
> mem_cgroup_uncharge_cache_page(page);
>
> if (freepage != NULL)
> @@ -510,7 +544,10 @@ static int __remove_mapping(struct address_space *mapping, struct page *page)
> return 1;
>
> cannot_free:
> - spin_unlock_irq(&mapping->tree_lock);
> + if (irqcontext)
> + spin_unlock_irqrestore(&mapping->tree_lock, flags);
> + else
> + spin_unlock_irq(&mapping->tree_lock);
> return 0;
> }
>
> @@ -520,9 +557,10 @@ cannot_free:
> * successfully detached, return 1. Assumes the caller has a single ref on
> * this page.
> */
> -int remove_mapping(struct address_space *mapping, struct page *page)
> +int remove_mapping(struct address_space *mapping, struct page *page,
> + bool irqcontext)
> {
> - if (__remove_mapping(mapping, page)) {
> + if (__remove_mapping(mapping, page, irqcontext)) {
> /*
> * Unfreezing the refcount with 1 rather than 2 effectively
> * drops the pagecache ref for us without requiring another
> @@ -904,7 +942,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> }
> }
>
> - if (!mapping || !__remove_mapping(mapping, page))
> + if (!mapping || !__remove_mapping(mapping, page, false))
> goto keep_locked;
>
> /*
> --
> 1.8.2.1
>
--
Michal Hocko
SUSE Labs
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