From a528910e12ec7ee203095eb1711468a66b9b60b0 Mon Sep 17 00:00:00 2001 From: Johannes Weiner Date: Thu, 3 Apr 2014 14:47:51 -0700 Subject: mm: thrash detection-based file cache sizing The VM maintains cached filesystem pages on two types of lists. One list holds the pages recently faulted into the cache, the other list holds pages that have been referenced repeatedly on that first list. The idea is to prefer reclaiming young pages over those that have shown to benefit from caching in the past. We call the recently usedbut ultimately was not significantly better than a FIFO policy and still thrashed cache based on eviction speed, rather than actual demand for cache. This patch solves one half of the problem by decoupling the ability to detect working set changes from the inactive list size. By maintaining a history of recently evicted file pages it can detect frequently used pages with an arbitrarily small inactive list size, and subsequently apply pressure on the active list based on actual demand for cache, not just overall eviction speed. Every zone maintains a counter that tracks inactive list aging speed. When a page is evicted, a snapshot of this counter is stored in the now-empty page cache radix tree slot. On refault, the minimum access distance of the page can be assessed, to evaluate whether the page should be part of the active list or not. This fixes the VM's blindness towards working set changes in excess of the inactive list. And it's the foundation to further improve the protection ability and reduce the minimum inactive list size of 50%. Signed-off-by: Johannes Weiner Reviewed-by: Rik van Riel Reviewed-by: Minchan Kim Reviewed-by: Bob Liu Cc: Andrea Arcangeli Cc: Christoph Hellwig Cc: Dave Chinner Cc: Greg Thelen Cc: Hugh Dickins Cc: Jan Kara Cc: KOSAKI Motohiro Cc: Luigi Semenzato Cc: Mel Gorman Cc: Metin Doslu Cc: Michel Lespinasse Cc: Ozgun Erdogan Cc: Peter Zijlstra Cc: Roman Gushchin Cc: Ryan Mallon Cc: Tejun Heo Cc: Vlastimil Babka Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/swap.h | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'include/linux/swap.h') diff --git a/include/linux/swap.h b/include/linux/swap.h index 46ba0c6c219f..b83cf61403ed 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -260,6 +260,11 @@ struct swap_list_t { int next; /* swapfile to be used next */ }; +/* linux/mm/workingset.c */ +void *workingset_eviction(struct address_space *mapping, struct page *page); +bool workingset_refault(void *shadow); +void workingset_activation(struct page *page); + /* linux/mm/page_alloc.c */ extern unsigned long totalram_pages; extern unsigned long totalreserve_pages; -- cgit From 449dd6984d0e47643c04c807f609dd56d48d5bcc Mon Sep 17 00:00:00 2001 From: Johannes Weiner Date: Thu, 3 Apr 2014 14:47:56 -0700 Subject: mm: keep page cache radix tree nodes in check Previously, page cache radix tree nodes were freed after reclaim emptied out their page pointers. But now reclaim stores shadow entries in their place, which are only reclaimed when the inodes themselves are reclaimed. This is problematic for bigger files that are still in use after they have a significant amount of their cache reclaimed, without any of those pages actually refaulting. The shadow entries will just sit there and waste memory. In the worst case, the shadow entries will accumulate until the machine runs out of memory. To get this under control, the VM will track radix tree nodes exclusively containing shadow entries on a per-NUMA node list. Per-NUMA rather than global because we expect the radix tree nodes themselves to be allocated node-locally and we want to reduce cross-node references of otherwise independent cache workloads. A simple shrinker will then reclaim these nodes on memory pressure. A few things need to be stored in the radix tree node to implement the shadow node LRU and allow tree deletions coming from the list: 1. There is no index available that would describe the reverse path from the node up to the tree root, which is needed to perform a deletion. To solve this, encode in each node its offset inside the parent. This can be stored in the unused upper bits of the same member that stores the node's height at no extra space cost. 2. The number of shadow entries needs to be counted in addition to the regular entries, to quickly detect when the node is ready to go to the shadow node LRU list. The current entry count is an unsigned int but the maximum number of entries is 64, so a shadow counter can easily be stored in the unused upper bits. 3. Tree modification needs tree lock and tree root, which are located in the address space, so store an address_space backpointer in the node. The parent pointer of the node is in a union with the 2-word rcu_head, so the backpointer comes at no extra cost as well. 4. The node needs to be linked to an LRU list, which requires a list head inside the node. This does increase the size of the node, but it does not change the number of objects that fit into a slab page. [akpm@linux-foundation.org: export the right function] Signed-off-by: Johannes Weiner Reviewed-by: Rik van Riel Reviewed-by: Minchan Kim Cc: Andrea Arcangeli Cc: Bob Liu Cc: Christoph Hellwig Cc: Dave Chinner Cc: Greg Thelen Cc: Hugh Dickins Cc: Jan Kara Cc: KOSAKI Motohiro Cc: Luigi Semenzato Cc: Mel Gorman Cc: Metin Doslu Cc: Michel Lespinasse Cc: Ozgun Erdogan Cc: Peter Zijlstra Cc: Roman Gushchin Cc: Ryan Mallon Cc: Tejun Heo Cc: Vlastimil Babka Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/swap.h | 31 +++++++++++++++++++++++++++++++ 1 file changed, 31 insertions(+) (limited to 'include/linux/swap.h') diff --git a/include/linux/swap.h b/include/linux/swap.h index b83cf61403ed..350711560753 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -264,6 +264,37 @@ struct swap_list_t { void *workingset_eviction(struct address_space *mapping, struct page *page); bool workingset_refault(void *shadow); void workingset_activation(struct page *page); +extern struct list_lru workingset_shadow_nodes; + +static inline unsigned int workingset_node_pages(struct radix_tree_node *node) +{ + return node->count & RADIX_TREE_COUNT_MASK; +} + +static inline void workingset_node_pages_inc(struct radix_tree_node *node) +{ + node->count++; +} + +static inline void workingset_node_pages_dec(struct radix_tree_node *node) +{ + node->count--; +} + +static inline unsigned int workingset_node_shadows(struct radix_tree_node *node) +{ + return node->count >> RADIX_TREE_COUNT_SHIFT; +} + +static inline void workingset_node_shadows_inc(struct radix_tree_node *node) +{ + node->count += 1U << RADIX_TREE_COUNT_SHIFT; +} + +static inline void workingset_node_shadows_dec(struct radix_tree_node *node) +{ + node->count -= 1U << RADIX_TREE_COUNT_SHIFT; +} /* linux/mm/page_alloc.c */ extern unsigned long totalram_pages; -- cgit