On 9/13/2023 12:28 AM, Zi Yan wrote:
From: Zi Yan <ziy@xxxxxxxxxx>
Before, memory compaction only migrates order-0 folios and skips >0 order
folios. This commit adds support for >0 order folio compaction by keeping
isolated free pages at their original size without splitting them into
order-0 pages and using them directly during migration process.
What is different from the prior implementation:
1. All isolated free pages are kept in a MAX_ORDER+1 array of page lists,
where each page list stores free pages in the same order.
2. All free pages are not post_alloc_hook() processed nor buddy pages,
although their orders are stored in first page's private like buddy
pages.
3. During migration, in new page allocation time (i.e., in
compaction_alloc()), free pages are then processed by post_alloc_hook().
When migration fails and a new page is returned (i.e., in
compaction_free()), free pages are restored by reversing the
post_alloc_hook() operations.
Step 3 is done for a latter optimization that splitting and/or merging free
pages during compaction becomes easier.
Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
---
mm/compaction.c | 108 +++++++++++++++++++++++++++++++++++++++---------
mm/internal.h | 7 +++-
2 files changed, 94 insertions(+), 21 deletions(-)
diff --git a/mm/compaction.c b/mm/compaction.c
index 01ba298739dd..868e92e55d27 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -107,6 +107,44 @@ static void split_map_pages(struct list_head *list)
list_splice(&tmp_list, list);
}
+static unsigned long release_free_list(struct free_list *freepages)
+{
+ int order;
+ unsigned long high_pfn = 0;
+
+ for (order = 0; order <= MAX_ORDER; order++) {
+ struct page *page, *next;
+
+ list_for_each_entry_safe(page, next, &freepages[order].pages, lru) {
+ unsigned long pfn = page_to_pfn(page);
+
+ list_del(&page->lru);
+ /*
+ * Convert free pages into post allocation pages, so
+ * that we can free them via __free_page.
+ */
+ post_alloc_hook(page, order, __GFP_MOVABLE);
+ __free_pages(page, order);
+ if (pfn > high_pfn)
+ high_pfn = pfn;
+ }
+ }
+ return high_pfn;
+}
+
+static void sort_free_pages(struct list_head *src, struct free_list *dst)
+{
+ unsigned int order;
+ struct page *page, *next;
+
+ list_for_each_entry_safe(page, next, src, lru) {
+ order = buddy_order(page);
These pages are already isolated from the buddy system, but continue to
use buddy_order() to get the page order, which can be confused.
Moreover, the buddy_order() should be under the zone lock protection.
IMO, just use 'page_private()' to get the page order like
split_map_pages() already did, that seems more readable.
+
+ list_move(&page->lru, &dst[order].pages);
+ dst[order].nr_free++;
+ }
+}
+
#ifdef CONFIG_COMPACTION
bool PageMovable(struct page *page)
{
@@ -1422,6 +1460,7 @@ fast_isolate_around(struct compact_control *cc, unsigned long pfn)
{
unsigned long start_pfn, end_pfn;
struct page *page;
+ LIST_HEAD(freelist);
/* Do not search around if there are enough pages already */
if (cc->nr_freepages >= cc->nr_migratepages)
@@ -1439,7 +1478,8 @@ fast_isolate_around(struct compact_control *cc, unsigned long pfn)
if (!page)
return;
- isolate_freepages_block(cc, &start_pfn, end_pfn, &cc->freepages, 1, false);
+ isolate_freepages_block(cc, &start_pfn, end_pfn, &freelist, 1, false);
+ sort_free_pages(&freelist, cc->freepages);
/* Skip this pageblock in the future as it's full or nearly full */
if (start_pfn == end_pfn && !cc->no_set_skip_hint)
@@ -1568,7 +1608,7 @@ static void fast_isolate_freepages(struct compact_control *cc)
nr_scanned += nr_isolated - 1;
total_isolated += nr_isolated;
cc->nr_freepages += nr_isolated;
- list_add_tail(&page->lru, &cc->freepages);
+ list_add_tail(&page->lru, &cc->freepages[order].pages);
Missed to update cc->freepages[order].nr_free?
count_compact_events(COMPACTISOLATED, nr_isolated);
} else {
/* If isolation fails, abort the search */
@@ -1642,13 +1682,13 @@ static void isolate_freepages(struct compact_control *cc)
unsigned long isolate_start_pfn; /* exact pfn we start at */
unsigned long block_end_pfn; /* end of current pageblock */
unsigned long low_pfn; /* lowest pfn scanner is able to scan */
- struct list_head *freelist = &cc->freepages;
unsigned int stride;
+ LIST_HEAD(freelist);
/* Try a small search of the free lists for a candidate */
fast_isolate_freepages(cc);
if (cc->nr_freepages)
- goto splitmap;
+ return;
/*
* Initialise the free scanner. The starting point is where we last
@@ -1708,7 +1748,8 @@ static void isolate_freepages(struct compact_control *cc)
/* Found a block suitable for isolating free pages from. */
nr_isolated = isolate_freepages_block(cc, &isolate_start_pfn,
- block_end_pfn, freelist, stride, false);
+ block_end_pfn, &freelist, stride, false);
+ sort_free_pages(&freelist, cc->freepages);
/* Update the skip hint if the full pageblock was scanned */
if (isolate_start_pfn == block_end_pfn)
@@ -1749,10 +1790,6 @@ static void isolate_freepages(struct compact_control *cc)
* and the loop terminated due to isolate_start_pfn < low_pfn
*/
cc->free_pfn = isolate_start_pfn;
-
-splitmap:
- /* __isolate_free_page() does not map the pages */
- split_map_pages(freelist);
}
/*
@@ -1763,18 +1800,21 @@ static struct folio *compaction_alloc(struct folio *src, unsigned long data)
{
struct compact_control *cc = (struct compact_control *)data;
struct folio *dst;
+ int order = folio_order(src);
- if (list_empty(&cc->freepages)) {
+ if (!cc->freepages[order].nr_free) {
isolate_freepages(cc);
-
- if (list_empty(&cc->freepages))
+ if (!cc->freepages[order].nr_free)
return NULL;
}
- dst = list_entry(cc->freepages.next, struct folio, lru);
+ dst = list_first_entry(&cc->freepages[order].pages, struct folio, lru);
+ cc->freepages[order].nr_free--;
list_del(&dst->lru);
- cc->nr_freepages--;
-
+ post_alloc_hook(&dst->page, order, __GFP_MOVABLE);
+ if (order)
+ prep_compound_page(&dst->page, order);
+ cc->nr_freepages -= 1 << order;
return dst;
}
@@ -1786,9 +1826,34 @@ static struct folio *compaction_alloc(struct folio *src, unsigned long data)
static void compaction_free(struct folio *dst, unsigned long data)
{
struct compact_control *cc = (struct compact_control *)data;
+ int order = folio_order(dst);
+ struct page *page = &dst->page;
- list_add(&dst->lru, &cc->freepages);
- cc->nr_freepages++;
+ if (order) {
+ int i;
+
+ page[1].flags &= ~PAGE_FLAGS_SECOND;
+ for (i = 1; i < (1 << order); i++) {
+ page[i].mapping = NULL;
+ clear_compound_head(&page[i]);
+ page[i].flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
+ }
+
+ }
+ /* revert post_alloc_hook() operations */
+ page->mapping = NULL;
+ page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
+ set_page_count(page, 0);
+ page_mapcount_reset(page);
+ reset_page_owner(page, order);
+ page_table_check_free(page, order);
+ arch_free_page(page, order);
+ set_page_private(page, order);
+ INIT_LIST_HEAD(&dst->lru);
+
+ list_add(&dst->lru, &cc->freepages[order].pages);
+ cc->freepages[order].nr_free++;
+ cc->nr_freepages += 1 << order;
}
/* possible outcome of isolate_migratepages */
@@ -2412,6 +2477,7 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)
const bool sync = cc->mode != MIGRATE_ASYNC;
bool update_cached;
unsigned int nr_succeeded = 0;
+ int order;
/*
* These counters track activities during zone compaction. Initialize
@@ -2421,7 +2487,10 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)
cc->total_free_scanned = 0;
cc->nr_migratepages = 0;
cc->nr_freepages = 0;
- INIT_LIST_HEAD(&cc->freepages);
+ for (order = 0; order <= MAX_ORDER; order++) {
+ INIT_LIST_HEAD(&cc->freepages[order].pages);
+ cc->freepages[order].nr_free = 0;
+ }
INIT_LIST_HEAD(&cc->migratepages);
cc->migratetype = gfp_migratetype(cc->gfp_mask);
@@ -2607,7 +2676,7 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)
* so we don't leave any returned pages behind in the next attempt.
*/
if (cc->nr_freepages > 0) {
- unsigned long free_pfn = release_freepages(&cc->freepages);
+ unsigned long free_pfn = release_free_list(cc->freepages);
cc->nr_freepages = 0;
VM_BUG_ON(free_pfn == 0);
@@ -2626,7 +2695,6 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)
trace_mm_compaction_end(cc, start_pfn, end_pfn, sync, ret);
- VM_BUG_ON(!list_empty(&cc->freepages));
VM_BUG_ON(!list_empty(&cc->migratepages));
return ret;
diff --git a/mm/internal.h b/mm/internal.h
index 8c90e966e9f8..f5c691bb5c1c 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -465,6 +465,11 @@ int split_free_page(struct page *free_page,
/*
* in mm/compaction.c
*/
+
+struct free_list {
+ struct list_head pages;
+ unsigned long nr_free;
+};
/*
* compact_control is used to track pages being migrated and the free pages
* they are being migrated to during memory compaction. The free_pfn starts
@@ -473,7 +478,7 @@ int split_free_page(struct page *free_page,
* completes when free_pfn <= migrate_pfn
*/
struct compact_control {
- struct list_head freepages; /* List of free pages to migrate to */
+ struct free_list freepages[MAX_ORDER + 1]; /* List of free pages to migrate to */
struct list_head migratepages; /* List of pages being migrated */
unsigned int nr_freepages; /* Number of isolated free pages */
unsigned int nr_migratepages; /* Number of pages to migrate */
