ceph: optimize pagevec iterating in ceph_writepages_start()

ceph_writepages_start() supports writing non-continuous pages.
If it encounters a non-dirty or non-writeable page in pagevec,
it can continue to check the rest pages in pagevec.

Signed-off-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
index 8526359c08b27034327a692db320b7c75bce94b4..5ca887bb5caeae48e535a8203ca7ab5f5cfa721b 100644 (file)
--- a/fs/ceph/addr.c
+++ b/fs/ceph/addr.c
@@ -851,7 +851,6 @@ retry:
 
        while (!done && index <= end) {
                unsigned i;
-               int first;
                pgoff_t strip_unit_end = 0;
                int num_ops = 0, op_idx;
                int pvec_pages, locked_pages = 0;
@@ -864,7 +863,6 @@ retry:
                max_pages = max_pages_ever;
 
 get_more_pages:
-               first = -1;
                want = min(end - index,
                           min((pgoff_t)PAGEVEC_SIZE,
                               max_pages - (pgoff_t)locked_pages) - 1)
@@ -888,7 +886,7 @@ get_more_pages:
                            unlikely(page->mapping != mapping)) {
                                dout("!dirty or !mapping %p\n", page);
                                unlock_page(page);
-                               break;
+                               continue;
                        }
                        if (!wbc->range_cyclic && page->index > end) {
                                dout("end of range %p\n", page);
@@ -901,10 +899,6 @@ get_more_pages:
                                unlock_page(page);
                                break;
                        }
-                       if (wbc->sync_mode != WB_SYNC_NONE) {
-                               dout("waiting on writeback %p\n", page);
-                               wait_on_page_writeback(page);
-                       }
                        if (page_offset(page) >= ceph_wbc.i_size) {
                                dout("%p page eof %llu\n",
                                     page, ceph_wbc.i_size);
@@ -913,9 +907,13 @@ get_more_pages:
                                break;
                        }
                        if (PageWriteback(page)) {
-                               dout("%p under writeback\n", page);
-                               unlock_page(page);
-                               break;
+                               if (wbc->sync_mode == WB_SYNC_NONE) {
+                                       dout("%p under writeback\n", page);
+                                       unlock_page(page);
+                                       continue;
+                               }
+                               dout("waiting on writeback %p\n", page);
+                               wait_on_page_writeback(page);
                        }
 
                        /* only if matching snap context */
@@ -924,15 +922,13 @@ get_more_pages:
                                dout("page snapc %p %lld > oldest %p %lld\n",
                                     pgsnapc, pgsnapc->seq, snapc, snapc->seq);
                                unlock_page(page);
-                               if (!locked_pages)
-                                       continue; /* keep looking for snap */
-                               break;
+                               continue;
                        }
 
                        if (!clear_page_dirty_for_io(page)) {
                                dout("%p !clear_page_dirty_for_io\n", page);
                                unlock_page(page);
-                               break;
+                               continue;
                        }
 
                        /*
@@ -988,8 +984,6 @@ get_more_pages:
                        }
 
                        /* note position of first page in pvec */
-                       if (first < 0)
-                               first = i;
                        dout("%p will write page %p idx %lu\n",
                             inode, page, page->index);
 
@@ -1000,8 +994,10 @@ get_more_pages:
                                                  BLK_RW_ASYNC);
                        }
 
-                       pages[locked_pages] = page;
-                       locked_pages++;
+
+                       pages[locked_pages++] = page;
+                       pvec.pages[i] = NULL;
+
                        len += PAGE_SIZE;
                }
 
@@ -1009,23 +1005,23 @@ get_more_pages:
                if (!locked_pages)
                        goto release_pvec_pages;
                if (i) {
-                       int j;
-                       BUG_ON(!locked_pages || first < 0);
+                       unsigned j, n = 0;
+                       /* shift unused page to beginning of pvec */
+                       for (j = 0; j < pvec_pages; j++) {
+                               if (!pvec.pages[j])
+                                       continue;
+                               if (n < j)
+                                       pvec.pages[n] = pvec.pages[j];
+                               n++;
+                       }
+                       pvec.nr = n;
 
                        if (pvec_pages && i == pvec_pages &&
                            locked_pages < max_pages) {
                                dout("reached end pvec, trying for more\n");
-                               pagevec_reinit(&pvec);
+                               pagevec_release(&pvec);
                                goto get_more_pages;
                        }
-
-                       /* shift unused pages over in the pvec...  we
-                        * will need to release them below. */
-                       for (j = i; j < pvec_pages; j++) {
-                               dout(" pvec leftover page %p\n", pvec.pages[j]);
-                               pvec.pages[j-i+first] = pvec.pages[j];
-                       }
-                       pvec.nr -= i-first;
                }
 
 new_request: