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mm: add_to_swap_cache() must not sleep
After commit 355cfa73
("mm: modify swap_map and add SWAP_HAS_CACHE flag"),
read_swap_cache_async() will busy-wait while a entry doesn't exist in swap
cache but it has SWAP_HAS_CACHE flag.
Such entries can exist on add/delete path of swap cache. On add path,
add_to_swap_cache() is called soon after SWAP_HAS_CACHE flag is set, and
on delete path, swapcache_free() will be called (SWAP_HAS_CACHE flag is
cleared) soon after __delete_from_swap_cache() is called. So, the
busy-wait works well in most cases.
But this mechanism can cause soft lockup if add_to_swap_cache() sleeps and
read_swap_cache_async() tries to swap-in the same entry on the same cpu.
This patch calls radix_tree_preload() before swapcache_prepare() and
divides add_to_swap_cache() into two part: radix_tree_preload() part and
radix_tree_insert() part(define it as __add_to_swap_cache()).
Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
parent
8fbb398f5c
commit
31a5639623
1 changed files with 46 additions and 24 deletions
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@ -67,10 +67,10 @@ void show_swap_cache_info(void)
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}
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/*
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* add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
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* __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
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* but sets SwapCache flag and private instead of mapping and index.
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*/
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int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
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static int __add_to_swap_cache(struct page *page, swp_entry_t entry)
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{
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int error;
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@ -78,28 +78,37 @@ int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
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VM_BUG_ON(PageSwapCache(page));
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VM_BUG_ON(!PageSwapBacked(page));
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page_cache_get(page);
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SetPageSwapCache(page);
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set_page_private(page, entry.val);
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spin_lock_irq(&swapper_space.tree_lock);
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error = radix_tree_insert(&swapper_space.page_tree, entry.val, page);
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if (likely(!error)) {
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total_swapcache_pages++;
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__inc_zone_page_state(page, NR_FILE_PAGES);
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INC_CACHE_INFO(add_total);
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}
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spin_unlock_irq(&swapper_space.tree_lock);
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if (unlikely(error)) {
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set_page_private(page, 0UL);
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ClearPageSwapCache(page);
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page_cache_release(page);
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}
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return error;
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}
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int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
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{
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int error;
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error = radix_tree_preload(gfp_mask);
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if (!error) {
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page_cache_get(page);
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SetPageSwapCache(page);
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set_page_private(page, entry.val);
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spin_lock_irq(&swapper_space.tree_lock);
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error = radix_tree_insert(&swapper_space.page_tree,
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entry.val, page);
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if (likely(!error)) {
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total_swapcache_pages++;
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__inc_zone_page_state(page, NR_FILE_PAGES);
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INC_CACHE_INFO(add_total);
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}
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spin_unlock_irq(&swapper_space.tree_lock);
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error = __add_to_swap_cache(page, entry);
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radix_tree_preload_end();
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if (unlikely(error)) {
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set_page_private(page, 0UL);
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ClearPageSwapCache(page);
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page_cache_release(page);
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}
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}
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return error;
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}
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@ -289,14 +298,25 @@ struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
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break; /* Out of memory */
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}
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/*
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* call radix_tree_preload() while we can wait.
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*/
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err = radix_tree_preload(gfp_mask & GFP_KERNEL);
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if (err)
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break;
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/*
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* Swap entry may have been freed since our caller observed it.
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*/
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err = swapcache_prepare(entry);
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if (err == -EEXIST) /* seems racy */
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if (err == -EEXIST) { /* seems racy */
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radix_tree_preload_end();
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continue;
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if (err) /* swp entry is obsolete ? */
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}
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if (err) { /* swp entry is obsolete ? */
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radix_tree_preload_end();
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break;
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}
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/*
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* Associate the page with swap entry in the swap cache.
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@ -308,8 +328,9 @@ struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
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*/
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__set_page_locked(new_page);
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SetPageSwapBacked(new_page);
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err = add_to_swap_cache(new_page, entry, gfp_mask & GFP_KERNEL);
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err = __add_to_swap_cache(new_page, entry);
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if (likely(!err)) {
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radix_tree_preload_end();
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/*
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* Initiate read into locked page and return.
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*/
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@ -317,6 +338,7 @@ struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
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swap_readpage(new_page);
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return new_page;
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}
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radix_tree_preload_end();
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ClearPageSwapBacked(new_page);
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__clear_page_locked(new_page);
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swapcache_free(entry, NULL);
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