readahead: move the random read case to bottom

[linux-block.git] / mm / readahead.c

diff --git a/mm/readahead.c b/mm/readahead.c
index a7f01fcce9e7958e155fbd8aee2ef1a9b2c28783..ceed7e4790bd99c4aa1e67fe3760a2c8ad8099d3 100644 (file)
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -339,33 +339,25 @@ ondemand_readahead(struct address_space *mapping,
                   unsigned long req_size)
 {
        unsigned long max = max_sane_readahead(ra->ra_pages);
-       pgoff_t prev_offset;
-       int     sequential;
+
+       /*
+        * start of file
+        */
+       if (!offset)
+               goto initial_readahead;
 
        /*
         * It's the expected callback offset, assume sequential access.
         * Ramp up sizes, and push forward the readahead window.
         */
-       if (offset && (offset == (ra->start + ra->size - ra->async_size) ||
-                       offset == (ra->start + ra->size))) {
+       if ((offset == (ra->start + ra->size - ra->async_size) ||
+            offset == (ra->start + ra->size))) {
                ra->start += ra->size;
                ra->size = get_next_ra_size(ra, max);
                ra->async_size = ra->size;
                goto readit;
        }
 
-       prev_offset = ra->prev_pos >> PAGE_CACHE_SHIFT;
-       sequential = offset - prev_offset <= 1UL || req_size > max;
-
-       /*
-        * Standalone, small read.
-        * Read as is, and do not pollute the readahead state.
-        */
-       if (!hit_readahead_marker && !sequential) {
-               return __do_page_cache_readahead(mapping, filp,
-                                               offset, req_size, 0);
-       }
-
        /*
         * Hit a marked page without valid readahead state.
         * E.g. interleaved reads.
@@ -391,12 +383,24 @@ ondemand_readahead(struct address_space *mapping,
        }
 
        /*
-        * It may be one of
-        *      - first read on start of file
-        *      - sequential cache miss
-        *      - oversize random read
-        * Start readahead for it.
+        * oversize read
         */
+       if (req_size > max)
+               goto initial_readahead;
+
+       /*
+        * sequential cache miss
+        */
+       if (offset - (ra->prev_pos >> PAGE_CACHE_SHIFT) <= 1UL)
+               goto initial_readahead;
+
+       /*
+        * standalone, small random read
+        * Read as is, and do not pollute the readahead state.
+        */
+       return __do_page_cache_readahead(mapping, filp, offset, req_size, 0);
+
+initial_readahead:
        ra->start = offset;
        ra->size = get_init_ra_size(req_size, max);
        ra->async_size = ra->size > req_size ? ra->size - req_size : ra->size;