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mm/compaction: cleanup isolate_freepages()

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isolate_freepages() is currently somewhat hard to follow thanks to many
looks like it is related to the 'low_pfn' variable, but in fact it is not.

This patch renames the 'high_pfn' variable to a hopefully less confusing name,
and slightly changes its handling without a functional change. A comment made
obsolete by recent changes is also updated.

[akpm@linux-foundation.org: comment fixes, per Minchan]
[iamjoonsoo.kim@lge.com: cleanups]
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
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: Michal Nazarewicz <mina86@mina86.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: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Vlastimil Babka 2014-06-04 16:07:26 -07:00 committed by Linus Torvalds
parent 13fb44e4b0
commit c96b9e508f
1 changed files with 27 additions and 29 deletions
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56
mm/compaction.c
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@ -665,7 +665,10 @@ static void isolate_freepages(struct zone *zone,
struct compact_control *cc)
{
struct page *page;
unsigned long high_pfn, low_pfn, pfn, z_end_pfn;
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 */
int nr_freepages = cc->nr_freepages;
struct list_head *freelist = &cc->freepages;
@ -673,32 +676,33 @@ 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);
/*
* Take care that if the migration scanner is at the end of the zone
* that the free scanner does not accidentally move to the next zone
* in the next isolation cycle.
* If no pages are isolated, the block_start_pfn < low_pfn check
* will kick in.
*/
high_pfn = min(low_pfn, pfn);
z_end_pfn = zone_end_pfn(zone);
next_free_pfn = 0;
/*
* 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
@ -707,7 +711,7 @@ static void isolate_freepages(struct zone *zone,
*/
cond_resched();
if (!pfn_valid(pfn))
if (!pfn_valid(block_start_pfn))
continue;
/*
@ -717,7 +721,7 @@ 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;
@ -730,14 +734,8 @@ 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;
/*
@ -745,9 +743,9 @@ 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;
high_pfn = max(high_pfn, pfn);
next_free_pfn = block_start_pfn;
}
}
@ -758,10 +756,10 @@ 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)
cc->free_pfn = max(pfn, zone->zone_start_pfn);
else
cc->free_pfn = high_pfn;
if (block_start_pfn < low_pfn)
next_free_pfn = cc->migrate_pfn;
cc->free_pfn = next_free_pfn;
cc->nr_freepages = nr_freepages;
}