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Subject[PATCH 6/9] 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>
---
mm/filemap.c | 51 +++++++++++++++++++++++++++++--------------------
1 file changed, 31 insertions(+), 20 deletions(-)
--- linux-2.6.22-rc1-mm1.orig/mm/filemap.c
+++ linux-2.6.22-rc1-mm1/mm/filemap.c
@@ -916,15 +916,20 @@ void do_generic_mapping_read(struct addr
nr = nr - offset;

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;
@@ -1075,6 +1080,7 @@ no_cached_page:

out:
*_ra = ra;
+ _ra->prev_index = prev_index;

*ppos = ((loff_t) index << PAGE_CACHE_SHIFT) + offset;
if (cached_page)
@@ -1378,26 +1384,30 @@ struct page *filemap_fault(struct vm_are
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, fdata->pgoff, 1);
-
- /*
* Do we have something in the page cache already?
*/
retry_find:
page = find_lock_page(mapping, fdata->pgoff);
+ /*
+ * For sequential accesses, we use the generic readahead logic.
+ */
+ if (VM_SequentialReadHint(vma)) {
+ if (!page) {
+ page_cache_readahead_ondemand(mapping, ra, file, page,
+ fdata->pgoff, 1);
+ page = find_lock_page(mapping, fdata->pgoff);
+ if (!page)
+ goto no_cached_page;
+ }
+ if (PageReadahead(page)) {
+ page_cache_readahead_ondemand(mapping, ra, file, page,
+ fdata->pgoff, 1);
+ }
+ }
+
if (!page) {
unsigned long ra_pages;

- if (VM_SequentialReadHint(vma)) {
- handle_ra_miss(mapping, ra, fdata->pgoff);
- goto no_cached_page;
- }
ra->mmap_miss++;

/*
@@ -1450,6 +1460,7 @@ retry_find:
* Found the page and have a reference on it.
*/
mark_page_accessed(page);
+ ra->prev_index = page->index;
return page;

outside_data_content:
--
-
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