readahead: record mmap read-around states in file_ra_state

Mmap read-around now shares the same code style and data structure with
readahead code.

This also removes do_page_cache_readahead().  Its last user, mmap
read-around, has been changed to call ra_submit().

The no-readahead-if-congested logic is dumped by the way.  Users will be
pretty sensitive about the slow loading of executables.  So it's
unfavorable to disabled mmap read-around on a congested queue.

[akpm@linux-foundation.org: coding-style fixes]
Cc: Nick Piggin <npiggin@suse.de>
Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
Cc: Ying Han <yinghan@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/mm.h

@@ -1178,8 +1178,6 @@ void task_dirty_inc(struct task_struct *tsk);
 #define VM_MAX_READAHEAD	128	/* kbytes */
 #define VM_MIN_READAHEAD	16	/* kbytes (includes current page) */
 
-int do_page_cache_readahead(struct address_space *mapping, struct file *filp,
-			pgoff_t offset, unsigned long nr_to_read);
 int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
 			pgoff_t offset, unsigned long nr_to_read);
 
@@ -1197,6 +1195,9 @@ void page_cache_async_readahead(struct address_space *mapping,
 				unsigned long size);
 
 unsigned long max_sane_readahead(unsigned long nr);
+unsigned long ra_submit(struct file_ra_state *ra,
+			struct address_space *mapping,
+			struct file *filp);
 
 /* Do stack extension */
 extern int expand_stack(struct vm_area_struct *vma, unsigned long address);

mm/filemap.c

@@ -1488,13 +1488,15 @@ static void do_sync_mmap_readahead(struct vm_area_struct *vma,
 	if (ra->mmap_miss > MMAP_LOTSAMISS)
 		return;
 
+	/*
+	 * mmap read-around
+	 */
 	ra_pages = max_sane_readahead(ra->ra_pages);
 	if (ra_pages) {
-		pgoff_t start = 0;
-
-		if (offset > ra_pages / 2)
-			start = offset - ra_pages / 2;
-		do_page_cache_readahead(mapping, file, start, ra_pages);
+		ra->start = max_t(long, 0, offset - ra_pages/2);
+		ra->size = ra_pages;
+		ra->async_size = 0;
+		ra_submit(ra, mapping, file);
 	}
 }
 

mm/readahead.c

@@ -133,15 +133,12 @@ static int read_pages(struct address_space *mapping, struct file *filp,
 }
 
 /*
- * do_page_cache_readahead actually reads a chunk of disk.  It allocates all
+ * __do_page_cache_readahead() actually reads a chunk of disk.  It allocates all
  * the pages first, then submits them all for I/O. This avoids the very bad
  * behaviour which would occur if page allocations are causing VM writeback.
  * We really don't want to intermingle reads and writes like that.
  *
  * Returns the number of pages requested, or the maximum amount of I/O allowed.
- *
- * do_page_cache_readahead() returns -1 if it encountered request queue
- * congestion.
  */
 static int
 __do_page_cache_readahead(struct address_space *mapping, struct file *filp,
@@ -231,22 +228,6 @@ int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
 	return ret;
 }
 
-/*
- * This version skips the IO if the queue is read-congested, and will tell the
- * block layer to abandon the readahead if request allocation would block.
- *
- * force_page_cache_readahead() will ignore queue congestion and will block on
- * request queues.
- */
-int do_page_cache_readahead(struct address_space *mapping, struct file *filp,
-			pgoff_t offset, unsigned long nr_to_read)
-{
-	if (bdi_read_congested(mapping->backing_dev_info))
-		return -1;
-
-	return __do_page_cache_readahead(mapping, filp, offset, nr_to_read, 0);
-}
-
 /*
  * Given a desired number of PAGE_CACHE_SIZE readahead pages, return a
  * sensible upper limit.
@@ -260,7 +241,7 @@ unsigned long max_sane_readahead(unsigned long nr)
 /*
  * Submit IO for the read-ahead request in file_ra_state.
  */
-static unsigned long ra_submit(struct file_ra_state *ra,
+unsigned long ra_submit(struct file_ra_state *ra,
 		       struct address_space *mapping, struct file *filp)
 {
 	int actual;