readahead: convert filemap invocations

Convert filemap reads to use on-demand readahead.

The new call scheme is to
- call readahead on non-cached page
- call readahead on look-ahead page
- update prev_index when finished with the read request

Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
Cc: Steven Pratt <slpratt@austin.ibm.com>
Cc: Ram Pai <linuxram@us.ibm.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 31 insertions, 20 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index 4fd9e3f0f48a..5eb0a6b9d607 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -891,15 +891,20 @@ void do_generic_mapping_read(struct address_space *mapping,
                 unsigned long nr, ret;
 
                 cond_resched();
-                if (index == next_index)
-                        next_index = page_cache_readahead(mapping, &ra, filp,
-                                        index, last_index - index);
-
 find_page:
                 page = find_get_page(mapping, index);
-                if (unlikely(page == NULL)) {
-                        handle_ra_miss(mapping, &ra, index);
-                        goto no_cached_page;
+                if (!page) {
+                        page_cache_readahead_ondemand(mapping,
+                                        &ra, filp, page,
+                                        index, last_index - index);
+                        page = find_get_page(mapping, index);
+                        if (unlikely(page == NULL))
+                                goto no_cached_page;
+                }
+                if (PageReadahead(page)) {
+                        page_cache_readahead_ondemand(mapping,
+                                        &ra, filp, page,
+                                        index, last_index - index);
                 }
                 if (!PageUptodate(page))
                         goto page_not_up_to_date;
@@ -1051,6 +1056,7 @@ no_cached_page:
 
 out:
         *_ra = ra;
+        _ra->prev_index = prev_index;
 
         *ppos = ((loff_t) index << PAGE_CACHE_SHIFT) + offset;
         if (cached_page)
@@ -1333,26 +1339,30 @@ int filemap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
                 goto no_cached_page;
 
         /*
-         * The readahead code wants to be told about each and every page
-         * so it can build and shrink its windows appropriately
-         *
-         * For sequential accesses, we use the generic readahead logic.
-         */
-        if (VM_SequentialReadHint(vma))
-                page_cache_readahead(mapping, ra, file, vmf->pgoff, 1);
-
-        /*
          * Do we have something in the page cache already?
          */
 retry_find:
         page = find_lock_page(mapping, vmf->pgoff);
+        /*
+         * For sequential accesses, we use the generic readahead logic.
+         */
+        if (VM_SequentialReadHint(vma)) {
+                if (!page) {
+                        page_cache_readahead_ondemand(mapping, ra, file, page,
+                                                           vmf->pgoff, 1);
+                        page = find_lock_page(mapping, vmf->pgoff);
+                        if (!page)
+                                goto no_cached_page;
+                }
+                if (PageReadahead(page)) {
+                        page_cache_readahead_ondemand(mapping, ra, file, page,
+                                                           vmf->pgoff, 1);
+                }
+        }
+
         if (!page) {
                 unsigned long ra_pages;
 
-                if (VM_SequentialReadHint(vma)) {
-                        handle_ra_miss(mapping, ra, vmf->pgoff);
-                        goto no_cached_page;
-                }
                 ra->mmap_miss++;
 
                 /*
@@ -1405,6 +1415,7 @@ retry_find:
          * Found the page and have a reference on it.
          */
         mark_page_accessed(page);
+        ra->prev_index = page->index;
         vmf->page = page;
         return ret | VM_FAULT_LOCKED;