readahead: split ondemand readahead interface into two functions
Rusty Russell [Thu, 19 Jul 2007 08:48:08 +0000 (01:48 -0700)]
Split ondemand readahead interface into two functions.  I think this makes it
a little clearer for non-readahead experts (like Rusty).

Internally they both call ondemand_readahead(), but the page argument is
changed to an obvious boolean flag.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/ext3/dir.c
fs/ext4/dir.c
fs/splice.c
include/linux/mm.h
mm/filemap.c
mm/readahead.c

index 3c6d384..c00723a 100644 (file)
@@ -139,10 +139,10 @@ static int ext3_readdir(struct file * filp,
                        pgoff_t index = map_bh.b_blocknr >>
                                        (PAGE_CACHE_SHIFT - inode->i_blkbits);
                        if (!ra_has_index(&filp->f_ra, index))
-                               page_cache_readahead_ondemand(
+                               page_cache_sync_readahead(
                                        sb->s_bdev->bd_inode->i_mapping,
                                        &filp->f_ra, filp,
-                                       NULL, index, 1);
+                                       index, 1);
                        filp->f_ra.prev_index = index;
                        bh = ext3_bread(NULL, inode, blk, 0, &err);
                }
index 0a872a0..3ab01c0 100644 (file)
@@ -138,10 +138,10 @@ static int ext4_readdir(struct file * filp,
                        pgoff_t index = map_bh.b_blocknr >>
                                        (PAGE_CACHE_SHIFT - inode->i_blkbits);
                        if (!ra_has_index(&filp->f_ra, index))
-                               page_cache_readahead_ondemand(
+                               page_cache_sync_readahead(
                                        sb->s_bdev->bd_inode->i_mapping,
                                        &filp->f_ra, filp,
-                                       NULL, index, 1);
+                                       index, 1);
                        filp->f_ra.prev_index = index;
                        bh = ext4_bread(NULL, inode, blk, 0, &err);
                }
index 6ddd032..22496d2 100644 (file)
@@ -295,8 +295,8 @@ __generic_file_splice_read(struct file *in, loff_t *ppos,
         * readahead/allocate the rest and fill in the holes.
         */
        if (spd.nr_pages < nr_pages)
-               page_cache_readahead_ondemand(mapping, &in->f_ra, in,
-                               NULL, index, req_pages - spd.nr_pages);
+               page_cache_sync_readahead(mapping, &in->f_ra, in,
+                               index, req_pages - spd.nr_pages);
 
        error = 0;
        while (spd.nr_pages < nr_pages) {
@@ -352,7 +352,7 @@ __generic_file_splice_read(struct file *in, loff_t *ppos,
                page = pages[page_nr];
 
                if (PageReadahead(page))
-                       page_cache_readahead_ondemand(mapping, &in->f_ra, in,
+                       page_cache_async_readahead(mapping, &in->f_ra, in,
                                        page, index, req_pages - page_nr);
 
                /*
index 3d0d7d2..50a0ed1 100644 (file)
@@ -1138,12 +1138,20 @@ 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);
-unsigned long page_cache_readahead_ondemand(struct address_space *mapping,
-                         struct file_ra_state *ra,
-                         struct file *filp,
-                         struct page *page,
-                         pgoff_t offset,
-                         unsigned long size);
+
+void page_cache_sync_readahead(struct address_space *mapping,
+                              struct file_ra_state *ra,
+                              struct file *filp,
+                              pgoff_t offset,
+                              unsigned long size);
+
+void page_cache_async_readahead(struct address_space *mapping,
+                               struct file_ra_state *ra,
+                               struct file *filp,
+                               struct page *pg,
+                               pgoff_t offset,
+                               unsigned long size);
+
 unsigned long max_sane_readahead(unsigned long nr);
 
 /* Do stack extension */
index 5eb0a6b..49a6fe3 100644 (file)
@@ -894,15 +894,15 @@ void do_generic_mapping_read(struct address_space *mapping,
 find_page:
                page = find_get_page(mapping, index);
                if (!page) {
-                       page_cache_readahead_ondemand(mapping,
-                                       &ra, filp, page,
+                       page_cache_sync_readahead(mapping,
+                                       &ra, filp,
                                        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,
+                       page_cache_async_readahead(mapping,
                                        &ra, filp, page,
                                        index, last_index - index);
                }
@@ -1348,14 +1348,14 @@ retry_find:
         */
        if (VM_SequentialReadHint(vma)) {
                if (!page) {
-                       page_cache_readahead_ondemand(mapping, ra, file, page,
+                       page_cache_sync_readahead(mapping, ra, file,
                                                           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,
+                       page_cache_async_readahead(mapping, ra, file, page,
                                                           vmf->pgoff, 1);
                }
        }
index 205a4a4..3d262bb 100644 (file)
@@ -359,7 +359,7 @@ static unsigned long get_next_ra_size(struct file_ra_state *ra,
 static unsigned long
 ondemand_readahead(struct address_space *mapping,
                   struct file_ra_state *ra, struct file *filp,
-                  struct page *page, pgoff_t offset,
+                  bool hit_readahead_marker, pgoff_t offset,
                   unsigned long req_size)
 {
        unsigned long max;      /* max readahead pages */
@@ -387,7 +387,7 @@ ondemand_readahead(struct address_space *mapping,
         * Standalone, small read.
         * Read as is, and do not pollute the readahead state.
         */
-       if (!page && !sequential) {
+       if (!hit_readahead_marker && !sequential) {
                return __do_page_cache_readahead(mapping, filp,
                                                offset, req_size, 0);
        }
@@ -408,7 +408,7 @@ ondemand_readahead(struct address_space *mapping,
         * E.g. interleaved reads.
         * Not knowing its readahead pos/size, bet on the minimal possible one.
         */
-       if (page) {
+       if (hit_readahead_marker) {
                ra_index++;
                ra_size = min(4 * ra_size, max);
        }
@@ -421,50 +421,71 @@ fill_ra:
 }
 
 /**
- * page_cache_readahead_ondemand - generic file readahead
+ * page_cache_sync_readahead - generic file readahead
  * @mapping: address_space which holds the pagecache and I/O vectors
  * @ra: file_ra_state which holds the readahead state
  * @filp: passed on to ->readpage() and ->readpages()
- * @page: the page at @offset, or NULL if non-present
- * @offset: start offset into @mapping, in PAGE_CACHE_SIZE units
+ * @offset: start offset into @mapping, in pagecache page-sized units
  * @req_size: hint: total size of the read which the caller is performing in
- *            PAGE_CACHE_SIZE units
+ *            pagecache pages
  *
- * page_cache_readahead_ondemand() is the entry point of readahead logic.
- * This function should be called when it is time to perform readahead:
- * 1) @page == NULL
- *    A cache miss happened, time for synchronous readahead.
- * 2) @page != NULL && PageReadahead(@page)
- *    A look-ahead hit occured, time for asynchronous readahead.
+ * page_cache_sync_readahead() should be called when a cache miss happened:
+ * it will submit the read.  The readahead logic may decide to piggyback more
+ * pages onto the read request if access patterns suggest it will improve
+ * performance.
  */
-unsigned long
-page_cache_readahead_ondemand(struct address_space *mapping,
-                               struct file_ra_state *ra, struct file *filp,
-                               struct page *page, pgoff_t offset,
-                               unsigned long req_size)
+void page_cache_sync_readahead(struct address_space *mapping,
+                              struct file_ra_state *ra, struct file *filp,
+                              pgoff_t offset, unsigned long req_size)
 {
        /* no read-ahead */
        if (!ra->ra_pages)
-               return 0;
-
-       if (page) {
-               /*
-                * It can be PG_reclaim.
-                */
-               if (PageWriteback(page))
-                       return 0;
-
-               ClearPageReadahead(page);
-
-               /*
-                * Defer asynchronous read-ahead on IO congestion.
-                */
-               if (bdi_read_congested(mapping->backing_dev_info))
-                       return 0;
-       }
+               return;
+
+       /* do read-ahead */
+       ondemand_readahead(mapping, ra, filp, false, offset, req_size);
+}
+EXPORT_SYMBOL_GPL(page_cache_sync_readahead);
+
+/**
+ * page_cache_async_readahead - file readahead for marked pages
+ * @mapping: address_space which holds the pagecache and I/O vectors
+ * @ra: file_ra_state which holds the readahead state
+ * @filp: passed on to ->readpage() and ->readpages()
+ * @page: the page at @offset which has the PG_readahead flag set
+ * @offset: start offset into @mapping, in pagecache page-sized units
+ * @req_size: hint: total size of the read which the caller is performing in
+ *            pagecache pages
+ *
+ * page_cache_async_ondemand() should be called when a page is used which
+ * has the PG_readahead flag: this is a marker to suggest that the application
+ * has used up enough of the readahead window that we should start pulling in
+ * more pages. */
+void
+page_cache_async_readahead(struct address_space *mapping,
+                          struct file_ra_state *ra, struct file *filp,
+                          struct page *page, pgoff_t offset,
+                          unsigned long req_size)
+{
+       /* no read-ahead */
+       if (!ra->ra_pages)
+               return;
+
+       /*
+        * Same bit is used for PG_readahead and PG_reclaim.
+        */
+       if (PageWriteback(page))
+               return;
+
+       ClearPageReadahead(page);
+
+       /*
+        * Defer asynchronous read-ahead on IO congestion.
+        */
+       if (bdi_read_congested(mapping->backing_dev_info))
+               return;
 
        /* do read-ahead */
-       return ondemand_readahead(mapping, ra, filp, page,
-                                       offset, req_size);
+       ondemand_readahead(mapping, ra, filp, true, offset, req_size);
 }
-EXPORT_SYMBOL_GPL(page_cache_readahead_ondemand);
+EXPORT_SYMBOL_GPL(page_cache_async_readahead);