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authorVlastimil Babka <vbabka@suse.cz>2016-01-14 15:19:23 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2016-01-14 16:00:49 -0800
commit48131e03ca4ed71d73fbe55c311a258c6fa2a090 (patch)
tree2957b6c97152f31bd97e0943f36ab03ea49b6a19 /mm/shmem.c
parent6a15a37097c7e02390bb08d83dac433c9f10144f (diff)
downloadlwn-48131e03ca4ed71d73fbe55c311a258c6fa2a090.tar.gz
lwn-48131e03ca4ed71d73fbe55c311a258c6fa2a090.zip
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 <vbabka@suse.cz> Cc: Hugh Dickins <hughd@google.com> Cc: Jerome Marchand <jmarchan@redhat.com> Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru> Acked-by: Michal Hocko <mhocko@suse.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/shmem.c')
-rw-r--r--mm/shmem.c65
1 files changed, 38 insertions, 27 deletions
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();
@@ -430,6 +407,40 @@ restart:
}
/*
+ * 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.
*/
void shmem_unlock_mapping(struct address_space *mapping)