From 48131e03ca4ed71d73fbe55c311a258c6fa2a090 Mon Sep 17 00:00:00 2001 From: Vlastimil Babka Date: Thu, 14 Jan 2016 15:19:23 -0800 Subject: mm, proc: reduce cost of /proc/pid/smaps for unpopulated shmem mappings Following the previous patch, further reduction of /proc/pid/smaps cost is possible for private writable shmem mappings with unpopulated areas where the page walk invokes the .pte_hole function. We can use radix tree iterator for each such area instead of calling find_get_entry() in a loop. This is possible at the extra maintenance cost of introducing another shmem function shmem_partial_swap_usage(). To demonstrate the diference, I have measured this on a process that creates a private writable 2GB mapping of a partially swapped out /dev/shm/file (which cannot employ the optimizations from the prvious patch) and doesn't populate it at all. I time how long does it take to cat /proc/pid/smaps of this process 100 times. Before this patch: real 0m3.831s user 0m0.180s sys 0m3.212s After this patch: real 0m1.176s user 0m0.180s sys 0m0.684s The time is similar to the case where a radix tree iterator is employed on the whole mapping. Signed-off-by: Vlastimil Babka Cc: Hugh Dickins Cc: Jerome Marchand Cc: Konstantin Khlebnikov Acked-by: Michal Hocko Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/shmem.c | 65 ++++++++++++++++++++++++++++++++++++-------------------------- 1 file changed, 38 insertions(+), 27 deletions(-) (limited to 'mm') diff --git a/mm/shmem.c b/mm/shmem.c index e978621de1ef..760d90cf2a41 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -361,41 +361,18 @@ static int shmem_free_swap(struct address_space *mapping, /* * Determine (in bytes) how many of the shmem object's pages mapped by the - * given vma is swapped out. + * given offsets are swapped out. * * This is safe to call without i_mutex or mapping->tree_lock thanks to RCU, * as long as the inode doesn't go away and racy results are not a problem. */ -unsigned long shmem_swap_usage(struct vm_area_struct *vma) +unsigned long shmem_partial_swap_usage(struct address_space *mapping, + pgoff_t start, pgoff_t end) { - struct inode *inode = file_inode(vma->vm_file); - struct shmem_inode_info *info = SHMEM_I(inode); - struct address_space *mapping = inode->i_mapping; - unsigned long swapped; - pgoff_t start, end; struct radix_tree_iter iter; void **slot; struct page *page; - - /* Be careful as we don't hold info->lock */ - swapped = READ_ONCE(info->swapped); - - /* - * The easier cases are when the shmem object has nothing in swap, or - * the vma maps it whole. Then we can simply use the stats that we - * already track. - */ - if (!swapped) - return 0; - - if (!vma->vm_pgoff && vma->vm_end - vma->vm_start >= inode->i_size) - return swapped << PAGE_SHIFT; - - swapped = 0; - - /* Here comes the more involved part */ - start = linear_page_index(vma, vma->vm_start); - end = linear_page_index(vma, vma->vm_end); + unsigned long swapped = 0; rcu_read_lock(); @@ -429,6 +406,40 @@ restart: return swapped << PAGE_SHIFT; } +/* + * Determine (in bytes) how many of the shmem object's pages mapped by the + * given vma is swapped out. + * + * This is safe to call without i_mutex or mapping->tree_lock thanks to RCU, + * as long as the inode doesn't go away and racy results are not a problem. + */ +unsigned long shmem_swap_usage(struct vm_area_struct *vma) +{ + struct inode *inode = file_inode(vma->vm_file); + struct shmem_inode_info *info = SHMEM_I(inode); + struct address_space *mapping = inode->i_mapping; + unsigned long swapped; + + /* Be careful as we don't hold info->lock */ + swapped = READ_ONCE(info->swapped); + + /* + * The easier cases are when the shmem object has nothing in swap, or + * the vma maps it whole. Then we can simply use the stats that we + * already track. + */ + if (!swapped) + return 0; + + if (!vma->vm_pgoff && vma->vm_end - vma->vm_start >= inode->i_size) + return swapped << PAGE_SHIFT; + + /* Here comes the more involved part */ + return shmem_partial_swap_usage(mapping, + linear_page_index(vma, vma->vm_start), + linear_page_index(vma, vma->vm_end)); +} + /* * SysV IPC SHM_UNLOCK restore Unevictable pages to their evictable lists. */ -- cgit v1.2.3