From 6cc94b5acbf1a25fb78fd8c9123133c4bed67e2d Mon Sep 17 00:00:00 2001 From: Huang Ying Date: Sat, 10 Sep 2016 20:34:11 +1000 Subject: [PATCH] mm: don't use radix tree writeback tags for pages in swap cache MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit File pages use a set of radix tree tags (DIRTY, TOWRITE, WRITEBACK, etc.) to accelerate finding the pages with a specific tag in the radix tree during inode writeback. But for anonymous pages in the swap cache, there is no inode writeback. So there is no need to find the pages with some writeback tags in the radix tree. It is not necessary to touch radix tree writeback tags for pages in the swap cache. Per Rik van Riel's suggestion, a new flag AS_NO_WRITEBACK_TAGS is introduced for address spaces which don't need to update the writeback tags. The flag is set for swap caches. It may be used for DAX file systems, etc. With this patch, the swap out bandwidth improved 22.3% (from ~1.2GB/s to ~ 1.48GBps) in the vm-scalability swap-w-seq test case with 8 processes. The test is done on a Xeon E5 v3 system. The swap device used is a RAM simulated PMEM (persistent memory) device. The improvement comes from the reduced contention on the swap cache radix tree lock. To test sequential swapping out, the test case uses 8 processes, which sequentially allocate and write to the anonymous pages until RAM and part of the swap device is used up. Details of comparison is as follow, base base+patch ---------------- -------------------------- %stddev %change %stddev \ | \ 2506952 ± 2% +28.1% 3212076 ± 7% vm-scalability.throughput 1207402 ± 7% +22.3% 1476578 ± 6% vmstat.swap.so 10.86 ± 12% -23.4% 8.31 ± 16% perf-profile.cycles-pp._raw_spin_lock_irq.__add_to_swap_cache.add_to_swap_cache.add_to_swap.shrink_page_list 10.82 ± 13% -33.1% 7.24 ± 14% perf-profile.cycles-pp._raw_spin_lock_irqsave.__remove_mapping.shrink_page_list.shrink_inactive_list.shrink_zone_memcg 10.36 ± 11% -100.0% 0.00 ± -1% perf-profile.cycles-pp._raw_spin_lock_irqsave.__test_set_page_writeback.bdev_write_page.__swap_writepage.swap_writepage 10.52 ± 12% -100.0% 0.00 ± -1% perf-profile.cycles-pp._raw_spin_lock_irqsave.test_clear_page_writeback.end_page_writeback.page_endio.pmem_rw_page Link: http://lkml.kernel.org/r/1472578089-5560-1-git-send-email-ying.huang@intel.com Signed-off-by: "Huang, Ying" Acked-by: Rik van Riel Cc: Hugh Dickins Cc: Shaohua Li Cc: Minchan Kim Cc: Mel Gorman Cc: Tejun Heo Cc: Wu Fengguang Cc: Dave Hansen Signed-off-by: Andrew Morton --- include/linux/pagemap.h | 12 ++++++++++++ mm/page-writeback.c | 4 ++-- mm/swap_state.c | 2 ++ 3 files changed, 16 insertions(+), 2 deletions(-) diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index 66a1260b33de..2f5a65ddbebf 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -25,6 +25,8 @@ enum mapping_flags { AS_MM_ALL_LOCKS = __GFP_BITS_SHIFT + 2, /* under mm_take_all_locks() */ AS_UNEVICTABLE = __GFP_BITS_SHIFT + 3, /* e.g., ramdisk, SHM_LOCK */ AS_EXITING = __GFP_BITS_SHIFT + 4, /* final truncate in progress */ + /* writeback related tags are not used */ + AS_NO_WRITEBACK_TAGS = __GFP_BITS_SHIFT + 5, }; static inline void mapping_set_error(struct address_space *mapping, int error) @@ -64,6 +66,16 @@ static inline int mapping_exiting(struct address_space *mapping) return test_bit(AS_EXITING, &mapping->flags); } +static inline void mapping_set_no_writeback_tags(struct address_space *mapping) +{ + set_bit(AS_NO_WRITEBACK_TAGS, &mapping->flags); +} + +static inline int mapping_use_writeback_tags(struct address_space *mapping) +{ + return !test_bit(AS_NO_WRITEBACK_TAGS, &mapping->flags); +} + static inline gfp_t mapping_gfp_mask(struct address_space * mapping) { return (__force gfp_t)mapping->flags & __GFP_BITS_MASK; diff --git a/mm/page-writeback.c b/mm/page-writeback.c index 82e72524db55..67b7c8b55889 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -2728,7 +2728,7 @@ int test_clear_page_writeback(struct page *page) int ret; lock_page_memcg(page); - if (mapping) { + if (mapping && mapping_use_writeback_tags(mapping)) { struct inode *inode = mapping->host; struct backing_dev_info *bdi = inode_to_bdi(inode); unsigned long flags; @@ -2771,7 +2771,7 @@ int __test_set_page_writeback(struct page *page, bool keep_write) int ret; lock_page_memcg(page); - if (mapping) { + if (mapping && mapping_use_writeback_tags(mapping)) { struct inode *inode = mapping->host; struct backing_dev_info *bdi = inode_to_bdi(inode); unsigned long flags; diff --git a/mm/swap_state.c b/mm/swap_state.c index c8310a37be3a..268b8191982b 100644 --- a/mm/swap_state.c +++ b/mm/swap_state.c @@ -37,6 +37,8 @@ struct address_space swapper_spaces[MAX_SWAPFILES] = { .page_tree = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN), .i_mmap_writable = ATOMIC_INIT(0), .a_ops = &swap_aops, + /* swap cache doesn't use writeback related tags */ + .flags = 1 << AS_NO_WRITEBACK_TAGS, } }; -- 2.34.1