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>

diff --git a/mm/filemap.c b/mm/filemap.c
index 4fd9e3f..5eb0a6b 100644 (file)
--- 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)
@@ -1332,27 +1338,31 @@ int filemap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
        if (VM_RandomReadHint(vma))
                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;