mm: non-atomically mark page accessed during page cache allocation where possible

aops->write_begin may allocate a new page and make it visible only to have
mark_page_accessed called almost immediately after.  Once the page is
visible the atomic operations are necessary which is noticable overhead
when writing to an in-memory filesystem like tmpfs but should also be
noticable with fast storage.  The objective of the patch is to initialse
the accessed information with non-atomic operations before the page is
visible.

The bulk of filesystems directly or indirectly use
grab_cache_page_write_begin or find_or_create_page for the initial
allocation of a page cache page.  This patch adds an init_page_accessed()
helper which behaves like the first call to mark_page_accessed() but may
called before the page is visible and can be done non-atomically.

The primary APIs of concern in this care are the following and are used
by most filesystems.

	find_get_page
	find_lock_page
	find_or_create_page
	grab_cache_page_nowait
	grab_cache_page_write_begin

All of them are very similar in detail to the patch creates a core helper
pagecache_get_page() which takes a flags parameter that affects its
behavior such as whether the page should be marked accessed or not.  Then
old API is preserved but is basically a thin wrapper around this core
function.

Each of the filesystems are then updated to avoid calling
mark_page_accessed when it is known that the VM interfaces have already
done the job.  There is a slight snag in that the timing of the
mark_page_accessed() has now changed so in rare cases it's possible a page
gets to the end of the LRU as PageReferenced where as previously it might
have been repromoted.  This is expected to be rare but it's worth the
filesystem people thinking about it in case they see a problem with the
timing change.  It is also the case that some filesystems may be marking
pages accessed that previously did not but it makes sense that filesystems
have consistent behaviour in this regard.

The test case used to evaulate this is a simple dd of a large file done
multiple times with the file deleted on each iterations.  The size of the
file is 1/10th physical memory to avoid dirty page balancing.  In the
async case it will be possible that the workload completes without even
hitting the disk and will have variable results but highlight the impact
of mark_page_accessed for async IO.  The sync results are expected to be
more stable.  The exception is tmpfs where the normal case is for the "IO"
to not hit the disk.

The test machine was single socket and UMA to avoid any scheduling or NUMA
artifacts.  Throughput and wall times are presented for sync IO, only wall
times are shown for async as the granularity reported by dd and the
variability is unsuitable for comparison.  As async results were variable
do to writback timings, I'm only reporting the maximum figures.  The sync
results were stable enough to make the mean and stddev uninteresting.

The performance results are reported based on a run with no profiling.
Profile data is based on a separate run with oprofile running.

async dd
                                    3.15.0-rc3            3.15.0-rc3
                                       vanilla           accessed-v2
ext3    Max      elapsed     13.9900 (  0.00%)     11.5900 ( 17.16%)
tmpfs	Max      elapsed      0.5100 (  0.00%)      0.4900 (  3.92%)
btrfs   Max      elapsed     12.8100 (  0.00%)     12.7800 (  0.23%)
ext4	Max      elapsed     18.6000 (  0.00%)     13.3400 ( 28.28%)
xfs	Max      elapsed     12.5600 (  0.00%)      2.0900 ( 83.36%)

The XFS figure is a bit strange as it managed to avoid a worst case by
sheer luck but the average figures looked reasonable.

        samples percentage
ext3       86107    0.9783  vmlinux-3.15.0-rc4-vanilla        mark_page_accessed
ext3       23833    0.2710  vmlinux-3.15.0-rc4-accessed-v3r25 mark_page_accessed
ext3        5036    0.0573  vmlinux-3.15.0-rc4-accessed-v3r25 init_page_accessed
ext4       64566    0.8961  vmlinux-3.15.0-rc4-vanilla        mark_page_accessed
ext4        5322    0.0713  vmlinux-3.15.0-rc4-accessed-v3r25 mark_page_accessed
ext4        2869    0.0384  vmlinux-3.15.0-rc4-accessed-v3r25 init_page_accessed
xfs        62126    1.7675  vmlinux-3.15.0-rc4-vanilla        mark_page_accessed
xfs         1904    0.0554  vmlinux-3.15.0-rc4-accessed-v3r25 init_page_accessed
xfs          103    0.0030  vmlinux-3.15.0-rc4-accessed-v3r25 mark_page_accessed
btrfs      10655    0.1338  vmlinux-3.15.0-rc4-vanilla        mark_page_accessed
btrfs       2020    0.0273  vmlinux-3.15.0-rc4-accessed-v3r25 init_page_accessed
btrfs        587    0.0079  vmlinux-3.15.0-rc4-accessed-v3r25 mark_page_accessed
tmpfs      59562    3.2628  vmlinux-3.15.0-rc4-vanilla        mark_page_accessed
tmpfs       1210    0.0696  vmlinux-3.15.0-rc4-accessed-v3r25 init_page_accessed
tmpfs         94    0.0054  vmlinux-3.15.0-rc4-accessed-v3r25 mark_page_accessed

[akpm@linux-foundation.org: don't run init_page_accessed() against an uninitialised pointer]
Signed-off-by: Mel Gorman <mgorman@suse.de>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Jan Kara <jack@suse.cz>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Tested-by: Prabhakar Lad <prabhakar.csengg@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

11 files changed, 23 insertions, 28 deletions

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index f29a54e454d4..4cd0ac983f91 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -4510,7 +4510,8 @@ static void check_buffer_tree_ref(struct extent_buffer *eb)
         spin_unlock(&eb->refs_lock);
 }
 
-static void mark_extent_buffer_accessed(struct extent_buffer *eb)
+static void mark_extent_buffer_accessed(struct extent_buffer *eb,
+                struct page *accessed)
 {
         unsigned long num_pages, i;
 
@@ -4519,7 +4520,8 @@ static void mark_extent_buffer_accessed(struct extent_buffer *eb)
         num_pages = num_extent_pages(eb->start, eb->len);
         for (i = 0; i < num_pages; i++) {
                 struct page *p = extent_buffer_page(eb, i);
-                mark_page_accessed(p);
+                if (p != accessed)
+                        mark_page_accessed(p);
         }
 }
 
@@ -4533,7 +4535,7 @@ struct extent_buffer *find_extent_buffer(struct btrfs_fs_info *fs_info,
                                start >> PAGE_CACHE_SHIFT);
         if (eb && atomic_inc_not_zero(&eb->refs)) {
                 rcu_read_unlock();
-                mark_extent_buffer_accessed(eb);
+                mark_extent_buffer_accessed(eb, NULL);
                 return eb;
         }
         rcu_read_unlock();
@@ -4581,7 +4583,7 @@ struct extent_buffer *alloc_extent_buffer(struct btrfs_fs_info *fs_info,
                                 spin_unlock(&mapping->private_lock);
                                 unlock_page(p);
                                 page_cache_release(p);
-                                mark_extent_buffer_accessed(exists);
+                                mark_extent_buffer_accessed(exists, p);
                                 goto free_eb;
                         }
 
@@ -4596,7 +4598,6 @@ struct extent_buffer *alloc_extent_buffer(struct btrfs_fs_info *fs_info,
                 attach_extent_buffer_page(eb, p);
                 spin_unlock(&mapping->private_lock);
                 WARN_ON(PageDirty(p));
-                mark_page_accessed(p);
                 eb->pages[i] = p;
                 if (!PageUptodate(p))
                         uptodate = 0;
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index ae6af072b635..74272a3f9d9b 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -470,11 +470,12 @@ static void btrfs_drop_pages(struct page **pages, size_t num_pages)
         for (i = 0; i < num_pages; i++) {
                 /* page checked is some magic around finding pages that
                  * have been modified without going through btrfs_set_page_dirty
-                 * clear it here
+                 * clear it here. There should be no need to mark the pages
+                 * accessed as prepare_pages should have marked them accessed
+                 * in prepare_pages via find_or_create_page()
                  */
                 ClearPageChecked(pages[i]);
                 unlock_page(pages[i]);
-                mark_page_accessed(pages[i]);
                 page_cache_release(pages[i]);
         }
 }
diff --git a/fs/buffer.c b/fs/buffer.c
index 0d3e8d5a2299..eba6e4f621ce 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -227,7 +227,7 @@ __find_get_block_slow(struct block_device *bdev, sector_t block)
         int all_mapped = 1;
 
         index = block >> (PAGE_CACHE_SHIFT - bd_inode->i_blkbits);
-        page = find_get_page(bd_mapping, index);
+        page = find_get_page_flags(bd_mapping, index, FGP_ACCESSED);
         if (!page)
                 goto out;
 
@@ -1366,12 +1366,13 @@ __find_get_block(struct block_device *bdev, sector_t block, unsigned size)
         struct buffer_head *bh = lookup_bh_lru(bdev, block, size);
 
         if (bh == NULL) {
+                /* __find_get_block_slow will mark the page accessed */
                 bh = __find_get_block_slow(bdev, block);
                 if (bh)
                         bh_lru_install(bh);
-        }
-        if (bh)
+        } else
                 touch_buffer(bh);
+
         return bh;
 }
 EXPORT_SYMBOL(__find_get_block);
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index c8238a26818c..afe8a133e3d1 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -1044,6 +1044,8 @@ int ext4_mb_init_group(struct super_block *sb, ext4_group_t group)
          * allocating. If we are looking at the buddy cache we would
          * have taken a reference using ext4_mb_load_buddy and that
          * would have pinned buddy page to page cache.
+         * The call to ext4_mb_get_buddy_page_lock will mark the
+         * page accessed.
          */
         ret = ext4_mb_get_buddy_page_lock(sb, group, &e4b);
         if (ret || !EXT4_MB_GRP_NEED_INIT(this_grp)) {
@@ -1062,7 +1064,6 @@ int ext4_mb_init_group(struct super_block *sb, ext4_group_t group)
                 ret = -EIO;
                 goto err;
         }
-        mark_page_accessed(page);
 
         if (e4b.bd_buddy_page == NULL) {
                 /*
@@ -1082,7 +1083,6 @@ int ext4_mb_init_group(struct super_block *sb, ext4_group_t group)
                 ret = -EIO;
                 goto err;
         }
-        mark_page_accessed(page);
 err:
         ext4_mb_put_buddy_page_lock(&e4b);
         return ret;
@@ -1141,7 +1141,7 @@ ext4_mb_load_buddy(struct super_block *sb, ext4_group_t group,
 
         /* we could use find_or_create_page(), but it locks page
          * what we'd like to avoid in fast path ... */
-        page = find_get_page(inode->i_mapping, pnum);
+        page = find_get_page_flags(inode->i_mapping, pnum, FGP_ACCESSED);
         if (page == NULL || !PageUptodate(page)) {
                 if (page)
                         /*
@@ -1176,15 +1176,16 @@ ext4_mb_load_buddy(struct super_block *sb, ext4_group_t group,
                 ret = -EIO;
                 goto err;
         }
+
+        /* Pages marked accessed already */
         e4b->bd_bitmap_page = page;
         e4b->bd_bitmap = page_address(page) + (poff * sb->s_blocksize);
-        mark_page_accessed(page);
 
         block++;
         pnum = block / blocks_per_page;
         poff = block % blocks_per_page;
 
-        page = find_get_page(inode->i_mapping, pnum);
+        page = find_get_page_flags(inode->i_mapping, pnum, FGP_ACCESSED);
         if (page == NULL || !PageUptodate(page)) {
                 if (page)
                         page_cache_release(page);
@@ -1209,9 +1210,10 @@ ext4_mb_load_buddy(struct super_block *sb, ext4_group_t group,
                 ret = -EIO;
                 goto err;
         }
+
+        /* Pages marked accessed already */
         e4b->bd_buddy_page = page;
         e4b->bd_buddy = page_address(page) + (poff * sb->s_blocksize);
-        mark_page_accessed(page);
 
         BUG_ON(e4b->bd_bitmap_page == NULL);
         BUG_ON(e4b->bd_buddy_page == NULL);
diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
index 4aa521aa9bc3..c405b8f17054 100644
--- a/fs/f2fs/checkpoint.c
+++ b/fs/f2fs/checkpoint.c
@@ -69,7 +69,6 @@ repeat:
                 goto repeat;
         }
 out:
-        mark_page_accessed(page);
         return page;
 }
 
@@ -137,13 +136,11 @@ int ra_meta_pages(struct f2fs_sb_info *sbi, int start, int nrpages, int type)
                 if (!page)
                         continue;
                 if (PageUptodate(page)) {
-                        mark_page_accessed(page);
                         f2fs_put_page(page, 1);
                         continue;
                 }
 
                 f2fs_submit_page_mbio(sbi, page, blk_addr, &fio);
-                mark_page_accessed(page);
                 f2fs_put_page(page, 0);
         }
 out:
diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
index a161e955c4c8..57caa6eaf47b 100644
--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c
@@ -967,7 +967,6 @@ repeat:
                 goto repeat;
         }
 got_it:
-        mark_page_accessed(page);
         return page;
 }
 
@@ -1022,7 +1021,6 @@ page_hit:
                 f2fs_put_page(page, 1);
                 return ERR_PTR(-EIO);
         }
-        mark_page_accessed(page);
         return page;
 }
 
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index f680d2c44e97..903cbc9cd6bd 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1089,8 +1089,6 @@ static ssize_t fuse_fill_write_pages(struct fuse_req *req,
                 tmp = iov_iter_copy_from_user_atomic(page, ii, offset, bytes);
                 flush_dcache_page(page);
 
-                mark_page_accessed(page);
-
                 if (!tmp) {
                         unlock_page(page);
                         page_cache_release(page);
diff --git a/fs/gfs2/aops.c b/fs/gfs2/aops.c
index 5a49b037da81..492123cda64a 100644
--- a/fs/gfs2/aops.c
+++ b/fs/gfs2/aops.c
@@ -577,7 +577,6 @@ int gfs2_internal_read(struct gfs2_inode *ip, char *buf, loff_t *pos,
                 p = kmap_atomic(page);
                 memcpy(buf + copied, p + offset, amt);
                 kunmap_atomic(p);
-                mark_page_accessed(page);
                 page_cache_release(page);
                 copied += amt;
                 index++;
diff --git a/fs/gfs2/meta_io.c b/fs/gfs2/meta_io.c
index 2cf09b63a6b4..b984a6e190bc 100644
--- a/fs/gfs2/meta_io.c
+++ b/fs/gfs2/meta_io.c
@@ -136,7 +136,8 @@ struct buffer_head *gfs2_getbuf(struct gfs2_glock *gl, u64 blkno, int create)
                         yield();
                 }
         } else {
-                page = find_lock_page(mapping, index);
+                page = find_get_page_flags(mapping, index,
+                                                FGP_LOCK|FGP_ACCESSED);
                 if (!page)
                         return NULL;
         }
@@ -153,7 +154,6 @@ struct buffer_head *gfs2_getbuf(struct gfs2_glock *gl, u64 blkno, int create)
                 map_bh(bh, sdp->sd_vfs, blkno);
 
         unlock_page(page);
-        mark_page_accessed(page);
         page_cache_release(page);
 
         return bh;
diff --git a/fs/ntfs/attrib.c b/fs/ntfs/attrib.c
index a27e3fecefaf..250ed5b20c8f 100644
--- a/fs/ntfs/attrib.c
+++ b/fs/ntfs/attrib.c
@@ -1748,7 +1748,6 @@ int ntfs_attr_make_non_resident(ntfs_inode *ni, const u32 data_size)
         if (page) {
                 set_page_dirty(page);
                 unlock_page(page);
-                mark_page_accessed(page);
                 page_cache_release(page);
         }
         ntfs_debug("Done.");
diff --git a/fs/ntfs/file.c b/fs/ntfs/file.c
index db9bd8a31725..86ddab916b66 100644
--- a/fs/ntfs/file.c
+++ b/fs/ntfs/file.c
@@ -2060,7 +2060,6 @@ static ssize_t ntfs_file_buffered_write(struct kiocb *iocb,
                 }
                 do {
                         unlock_page(pages[--do_pages]);
-                        mark_page_accessed(pages[do_pages]);
                         page_cache_release(pages[do_pages]);
                 } while (do_pages);
                 if (unlikely(status))