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authorHuang Ying <ying.huang@intel.com>2017-09-07 02:24:36 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2017-09-07 03:27:29 +0300
commitec560175c0b6fce86994bdf036754d48122c5c87 (patch)
tree7aacd0beae098c785452a8a8361e13e7ffe2bc73 /include/linux/swap.h
parentc4fa63092f216737b60c789968371d9960a598e5 (diff)
downloadlinux-ec560175c0b6fce86994bdf036754d48122c5c87.tar.xz
mm, swap: VMA based swap readahead
The swap readahead is an important mechanism to reduce the swap in latency. Although pure sequential memory access pattern isn't very popular for anonymous memory, the space locality is still considered valid. In the original swap readahead implementation, the consecutive blocks in swap device are readahead based on the global space locality estimation. But the consecutive blocks in swap device just reflect the order of page reclaiming, don't necessarily reflect the access pattern in virtual memory. And the different tasks in the system may have different access patterns, which makes the global space locality estimation incorrect. In this patch, when page fault occurs, the virtual pages near the fault address will be readahead instead of the swap slots near the fault swap slot in swap device. This avoid to readahead the unrelated swap slots. At the same time, the swap readahead is changed to work on per-VMA from globally. So that the different access patterns of the different VMAs could be distinguished, and the different readahead policy could be applied accordingly. The original core readahead detection and scaling algorithm is reused, because it is an effect algorithm to detect the space locality. The test and result is as follow, Common test condition ===================== Test Machine: Xeon E5 v3 (2 sockets, 72 threads, 32G RAM) Swap device: NVMe disk Micro-benchmark with combined access pattern ============================================ vm-scalability, sequential swap test case, 4 processes to eat 50G virtual memory space, repeat the sequential memory writing until 300 seconds. The first round writing will trigger swap out, the following rounds will trigger sequential swap in and out. At the same time, run vm-scalability random swap test case in background, 8 processes to eat 30G virtual memory space, repeat the random memory write until 300 seconds. This will trigger random swap-in in the background. This is a combined workload with sequential and random memory accessing at the same time. The result (for sequential workload) is as follow, Base Optimized ---- --------- throughput 345413 KB/s 414029 KB/s (+19.9%) latency.average 97.14 us 61.06 us (-37.1%) latency.50th 2 us 1 us latency.60th 2 us 1 us latency.70th 98 us 2 us latency.80th 160 us 2 us latency.90th 260 us 217 us latency.95th 346 us 369 us latency.99th 1.34 ms 1.09 ms ra_hit% 52.69% 99.98% The original swap readahead algorithm is confused by the background random access workload, so readahead hit rate is lower. The VMA-base readahead algorithm works much better. Linpack ======= The test memory size is bigger than RAM to trigger swapping. Base Optimized ---- --------- elapsed_time 393.49 s 329.88 s (-16.2%) ra_hit% 86.21% 98.82% The score of base and optimized kernel hasn't visible changes. But the elapsed time reduced and readahead hit rate improved, so the optimized kernel runs better for startup and tear down stages. And the absolute value of readahead hit rate is high, shows that the space locality is still valid in some practical workloads. Link: http://lkml.kernel.org/r/20170807054038.1843-4-ying.huang@intel.com Signed-off-by: "Huang, Ying" <ying.huang@intel.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Minchan Kim <minchan@kernel.org> Cc: Rik van Riel <riel@redhat.com> Cc: Shaohua Li <shli@kernel.org> Cc: Hugh Dickins <hughd@google.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Cc: Tim Chen <tim.c.chen@intel.com> Cc: Dave Hansen <dave.hansen@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/linux/swap.h')
-rw-r--r--include/linux/swap.h57
1 files changed, 55 insertions, 2 deletions
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 76f1632eea5a..61d63379e956 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -251,6 +251,25 @@ struct swap_info_struct {
struct swap_cluster_list discard_clusters; /* discard clusters list */
};
+#ifdef CONFIG_64BIT
+#define SWAP_RA_ORDER_CEILING 5
+#else
+/* Avoid stack overflow, because we need to save part of page table */
+#define SWAP_RA_ORDER_CEILING 3
+#define SWAP_RA_PTE_CACHE_SIZE (1 << SWAP_RA_ORDER_CEILING)
+#endif
+
+struct vma_swap_readahead {
+ unsigned short win;
+ unsigned short offset;
+ unsigned short nr_pte;
+#ifdef CONFIG_64BIT
+ pte_t *ptes;
+#else
+ pte_t ptes[SWAP_RA_PTE_CACHE_SIZE];
+#endif
+};
+
/* linux/mm/workingset.c */
void *workingset_eviction(struct address_space *mapping, struct page *page);
bool workingset_refault(void *shadow);
@@ -350,6 +369,7 @@ int generic_swapfile_activate(struct swap_info_struct *, struct file *,
#define SWAP_ADDRESS_SPACE_SHIFT 14
#define SWAP_ADDRESS_SPACE_PAGES (1 << SWAP_ADDRESS_SPACE_SHIFT)
extern struct address_space *swapper_spaces[];
+extern bool swap_vma_readahead;
#define swap_address_space(entry) \
(&swapper_spaces[swp_type(entry)][swp_offset(entry) \
>> SWAP_ADDRESS_SPACE_SHIFT])
@@ -362,7 +382,9 @@ extern void __delete_from_swap_cache(struct page *);
extern void delete_from_swap_cache(struct page *);
extern void free_page_and_swap_cache(struct page *);
extern void free_pages_and_swap_cache(struct page **, int);
-extern struct page *lookup_swap_cache(swp_entry_t);
+extern struct page *lookup_swap_cache(swp_entry_t entry,
+ struct vm_area_struct *vma,
+ unsigned long addr);
extern struct page *read_swap_cache_async(swp_entry_t, gfp_t,
struct vm_area_struct *vma, unsigned long addr,
bool do_poll);
@@ -372,6 +394,17 @@ extern struct page *__read_swap_cache_async(swp_entry_t, gfp_t,
extern struct page *swapin_readahead(swp_entry_t, gfp_t,
struct vm_area_struct *vma, unsigned long addr);
+extern struct page *swap_readahead_detect(struct vm_fault *vmf,
+ struct vma_swap_readahead *swap_ra);
+extern struct page *do_swap_page_readahead(swp_entry_t fentry, gfp_t gfp_mask,
+ struct vm_fault *vmf,
+ struct vma_swap_readahead *swap_ra);
+
+static inline bool swap_use_vma_readahead(void)
+{
+ return READ_ONCE(swap_vma_readahead);
+}
+
/* linux/mm/swapfile.c */
extern atomic_long_t nr_swap_pages;
extern long total_swap_pages;
@@ -466,12 +499,32 @@ static inline struct page *swapin_readahead(swp_entry_t swp, gfp_t gfp_mask,
return NULL;
}
+static inline bool swap_use_vma_readahead(void)
+{
+ return false;
+}
+
+static inline struct page *swap_readahead_detect(
+ struct vm_fault *vmf, struct vma_swap_readahead *swap_ra)
+{
+ return NULL;
+}
+
+static inline struct page *do_swap_page_readahead(
+ swp_entry_t fentry, gfp_t gfp_mask,
+ struct vm_fault *vmf, struct vma_swap_readahead *swap_ra)
+{
+ return NULL;
+}
+
static inline int swap_writepage(struct page *p, struct writeback_control *wbc)
{
return 0;
}
-static inline struct page *lookup_swap_cache(swp_entry_t swp)
+static inline struct page *lookup_swap_cache(swp_entry_t swp,
+ struct vm_area_struct *vma,
+ unsigned long addr)
{
return NULL;
}