mm-compaction-cleanup-isolate_freepages-fix3

What I did here is taking end_pfn out of the loop and considering zone
boundary once.  After then, we can just set previous pfn to end_pfn on
every iteration to move scanning window.  With this change, we can remove
local variable, z_end_pfn.

Another things I did are removing max() operation and un-needed assignment
to isolate variable.

In addition, I change both the variable names, from pfn and end_pfn to
block_start_pfn and block_end_pfn, respectively.  They represent their
meaning perfectly.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: Vlastimil Babka <vbabka@suse.de>
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Dongjun Shin <d.j.shin@samsung.com>
Cc: Sunghwan Yun <sunghwan.yun@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/compaction.c b/mm/compaction.c
index 6a42ee508e6ccb4c7a39a42de14f311d265aff84..8e501566199c392cac771599b2ea1df288052f17 100644 (file)
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -662,10 +662,10 @@ static void isolate_freepages(struct zone *zone,
                                struct compact_control *cc)
 {
        struct page *page;
-       unsigned long pfn;           /* scanning cursor */
+       unsigned long block_start_pfn;  /* start of current pageblock */
+       unsigned long block_end_pfn;    /* end of current pageblock */
        unsigned long low_pfn;       /* lowest pfn scanner is able to scan */
        unsigned long next_free_pfn; /* start pfn for scaning at next round */
-       unsigned long z_end_pfn;     /* zone's end pfn */
        int nr_freepages = cc->nr_freepages;
        struct list_head *freelist = &cc->freepages;
 
@@ -673,31 +673,33 @@ static void isolate_freepages(struct zone *zone,
         * Initialise the free scanner. The starting point is where we last
         * successfully isolated from, zone-cached value, or the end of the
         * zone when isolating for the first time. We need this aligned to
-        * the pageblock boundary, because we do pfn -= pageblock_nr_pages
-        * in the for loop.
+        * the pageblock boundary, because we do
+        * block_start_pfn -= pageblock_nr_pages in the for loop.
+        * For ending point, take care when isolating in last pageblock of a
+        * a zone which ends in the middle of a pageblock.
         * The low boundary is the end of the pageblock the migration scanner
         * is using.
         */
-       pfn = cc->free_pfn & ~(pageblock_nr_pages-1);
+       block_start_pfn = cc->free_pfn & ~(pageblock_nr_pages-1);
+       block_end_pfn = min(block_start_pfn + pageblock_nr_pages,
+                                               zone_end_pfn(zone));
        low_pfn = ALIGN(cc->migrate_pfn + 1, pageblock_nr_pages);
 
        /*
-        * Seed the value for max(next_free_pfn, pfn) updates. If no pages are
-        * isolated, the pfn < low_pfn check will kick in.
+        * If no pages are isolated, the block_start_pfn < low_pfn check
+        * will kick in.
         */
        next_free_pfn = 0;
 
-       z_end_pfn = zone_end_pfn(zone);
-
        /*
         * Isolate free pages until enough are available to migrate the
         * pages on cc->migratepages. We stop searching if the migrate
         * and free page scanners meet or enough free pages are isolated.
         */
-       for (; pfn >= low_pfn && cc->nr_migratepages > nr_freepages;
-                                       pfn -= pageblock_nr_pages) {
+       for (; block_start_pfn >= low_pfn && cc->nr_migratepages > nr_freepages;
+                               block_end_pfn = block_start_pfn,
+                               block_start_pfn -= pageblock_nr_pages) {
                unsigned long isolated;
-               unsigned long end_pfn;
 
                /*
                 * This can iterate a massively long zone without finding any
@@ -706,7 +708,7 @@ static void isolate_freepages(struct zone *zone,
                 */
                cond_resched();
 
-               if (!pfn_valid(pfn))
+               if (!pfn_valid(block_start_pfn))
                        continue;
 
                /*
@@ -716,7 +718,7 @@ static void isolate_freepages(struct zone *zone,
                 * i.e. it's possible that all pages within a zones range of
                 * pages do not belong to a single zone.
                 */
-               page = pfn_to_page(pfn);
+               page = pfn_to_page(block_start_pfn);
                if (page_zone(page) != zone)
                        continue;
 
@@ -729,14 +731,8 @@ static void isolate_freepages(struct zone *zone,
                        continue;
 
                /* Found a block suitable for isolating free pages from */
-
-               /*
-                * Take care when isolating in last pageblock of a zone which
-                * ends in the middle of a pageblock.
-                */
-               end_pfn = min(pfn + pageblock_nr_pages, z_end_pfn);
-               isolated = isolate_freepages_block(cc, pfn, end_pfn,
-                                                  freelist, false);
+               isolated = isolate_freepages_block(cc, block_start_pfn,
+                                       block_end_pfn, freelist, false);
                nr_freepages += isolated;
 
                /*
@@ -744,9 +740,9 @@ static void isolate_freepages(struct zone *zone,
                 * looking for free pages, the search will restart here as
                 * page migration may have returned some pages to the allocator
                 */
-               if (isolated) {
+               if (isolated && next_free_pfn == 0) {
                        cc->finished_update_free = true;
-                       next_free_pfn = max(next_free_pfn, pfn);
+                       next_free_pfn = block_start_pfn;
                }
        }
 
@@ -757,7 +753,7 @@ static void isolate_freepages(struct zone *zone,
         * If we crossed the migrate scanner, we want to keep it that way
         * so that compact_finished() may detect this
         */
-       if (pfn < low_pfn)
+       if (block_start_pfn < low_pfn)
                next_free_pfn = cc->migrate_pfn;
 
        cc->free_pfn = next_free_pfn;