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mm, page_alloc: remove MIGRATE_RESERVE
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MIGRATE_RESERVE preserves an old property of the buddy allocator that
existed prior to fragmentation avoidance -- min_free_kbytes worth of pages
tended to remain contiguous until the only alternative was to fail the
allocation.  At the time it was discovered that high-order atomic
allocations relied on this property so MIGRATE_RESERVE was introduced.  A
later patch will introduce an alternative MIGRATE_HIGHATOMIC so this patch
deletes MIGRATE_RESERVE and supporting code so it'll be easier to review.
Note that this patch in isolation may look like a false regression if
someone was bisecting high-order atomic allocation failures.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Vitaly Wool <vitalywool@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Mel Gorman authored and Linus Torvalds committed Nov 7, 2015
1 parent f77cf4e commit 974a786
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Showing 4 changed files with 11 additions and 150 deletions.
10 changes: 2 additions & 8 deletions include/linux/mmzone.h
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Original file line number Diff line number Diff line change
Expand Up @@ -39,8 +39,6 @@ enum {
MIGRATE_UNMOVABLE,
MIGRATE_MOVABLE,
MIGRATE_RECLAIMABLE,
MIGRATE_PCPTYPES, /* the number of types on the pcp lists */
MIGRATE_RESERVE = MIGRATE_PCPTYPES,
#ifdef CONFIG_CMA
/*
* MIGRATE_CMA migration type is designed to mimic the way
Expand All @@ -63,6 +61,8 @@ enum {
MIGRATE_TYPES
};

#define MIGRATE_PCPTYPES (MIGRATE_RECLAIMABLE+1)

#ifdef CONFIG_CMA
# define is_migrate_cma(migratetype) unlikely((migratetype) == MIGRATE_CMA)
#else
Expand Down Expand Up @@ -429,12 +429,6 @@ struct zone {

const char *name;

/*
* Number of MIGRATE_RESERVE page block. To maintain for just
* optimization. Protected by zone->lock.
*/
int nr_migrate_reserve_block;

#ifdef CONFIG_MEMORY_ISOLATION
/*
* Number of isolated pageblock. It is used to solve incorrect
Expand Down
2 changes: 1 addition & 1 deletion mm/huge_memory.c
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Original file line number Diff line number Diff line change
Expand Up @@ -116,7 +116,7 @@ static void set_recommended_min_free_kbytes(void)
for_each_populated_zone(zone)
nr_zones++;

/* Make sure at least 2 hugepages are free for MIGRATE_RESERVE */
/* Ensure 2 pageblocks are free to assist fragmentation avoidance */
recommended_min = pageblock_nr_pages * nr_zones * 2;

/*
Expand Down
148 changes: 8 additions & 140 deletions mm/page_alloc.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -817,7 +817,6 @@ static void free_pcppages_bulk(struct zone *zone, int count,
if (unlikely(has_isolate_pageblock(zone)))
mt = get_pageblock_migratetype(page);

/* MIGRATE_MOVABLE list may include MIGRATE_RESERVEs */
__free_one_page(page, page_to_pfn(page), zone, 0, mt);
trace_mm_page_pcpu_drain(page, 0, mt);
} while (--to_free && --batch_free && !list_empty(list));
Expand Down Expand Up @@ -1417,15 +1416,14 @@ struct page *__rmqueue_smallest(struct zone *zone, unsigned int order,
* the free lists for the desirable migrate type are depleted
*/
static int fallbacks[MIGRATE_TYPES][4] = {
[MIGRATE_UNMOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_MOVABLE, MIGRATE_RESERVE },
[MIGRATE_RECLAIMABLE] = { MIGRATE_UNMOVABLE, MIGRATE_MOVABLE, MIGRATE_RESERVE },
[MIGRATE_MOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE, MIGRATE_RESERVE },
[MIGRATE_UNMOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_MOVABLE, MIGRATE_TYPES },
[MIGRATE_RECLAIMABLE] = { MIGRATE_UNMOVABLE, MIGRATE_MOVABLE, MIGRATE_TYPES },
[MIGRATE_MOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE, MIGRATE_TYPES },
#ifdef CONFIG_CMA
[MIGRATE_CMA] = { MIGRATE_RESERVE }, /* Never used */
[MIGRATE_CMA] = { MIGRATE_TYPES }, /* Never used */
#endif
[MIGRATE_RESERVE] = { MIGRATE_RESERVE }, /* Never used */
#ifdef CONFIG_MEMORY_ISOLATION
[MIGRATE_ISOLATE] = { MIGRATE_RESERVE }, /* Never used */
[MIGRATE_ISOLATE] = { MIGRATE_TYPES }, /* Never used */
#endif
};

Expand Down Expand Up @@ -1598,7 +1596,7 @@ int find_suitable_fallback(struct free_area *area, unsigned int order,
*can_steal = false;
for (i = 0;; i++) {
fallback_mt = fallbacks[migratetype][i];
if (fallback_mt == MIGRATE_RESERVE)
if (fallback_mt == MIGRATE_TYPES)
break;

if (list_empty(&area->free_list[fallback_mt]))
Expand Down Expand Up @@ -1676,25 +1674,13 @@ static struct page *__rmqueue(struct zone *zone, unsigned int order,
{
struct page *page;

retry_reserve:
page = __rmqueue_smallest(zone, order, migratetype);

if (unlikely(!page) && migratetype != MIGRATE_RESERVE) {
if (unlikely(!page)) {
if (migratetype == MIGRATE_MOVABLE)
page = __rmqueue_cma_fallback(zone, order);

if (!page)
page = __rmqueue_fallback(zone, order, migratetype);

/*
* Use MIGRATE_RESERVE rather than fail an allocation. goto
* is used because __rmqueue_smallest is an inline function
* and we want just one call site
*/
if (!page) {
migratetype = MIGRATE_RESERVE;
goto retry_reserve;
}
}

trace_mm_page_alloc_zone_locked(page, order, migratetype);
Expand Down Expand Up @@ -3492,7 +3478,6 @@ static void show_migration_types(unsigned char type)
[MIGRATE_UNMOVABLE] = 'U',
[MIGRATE_RECLAIMABLE] = 'E',
[MIGRATE_MOVABLE] = 'M',
[MIGRATE_RESERVE] = 'R',
#ifdef CONFIG_CMA
[MIGRATE_CMA] = 'C',
#endif
Expand Down Expand Up @@ -4302,120 +4287,6 @@ static inline unsigned long wait_table_bits(unsigned long size)
return ffz(~size);
}

/*
* Check if a pageblock contains reserved pages
*/
static int pageblock_is_reserved(unsigned long start_pfn, unsigned long end_pfn)
{
unsigned long pfn;

for (pfn = start_pfn; pfn < end_pfn; pfn++) {
if (!pfn_valid_within(pfn) || PageReserved(pfn_to_page(pfn)))
return 1;
}
return 0;
}

/*
* Mark a number of pageblocks as MIGRATE_RESERVE. The number
* of blocks reserved is based on min_wmark_pages(zone). The memory within
* the reserve will tend to store contiguous free pages. Setting min_free_kbytes
* higher will lead to a bigger reserve which will get freed as contiguous
* blocks as reclaim kicks in
*/
static void setup_zone_migrate_reserve(struct zone *zone)
{
unsigned long start_pfn, pfn, end_pfn, block_end_pfn;
struct page *page;
unsigned long block_migratetype;
int reserve;
int old_reserve;

/*
* Get the start pfn, end pfn and the number of blocks to reserve
* We have to be careful to be aligned to pageblock_nr_pages to
* make sure that we always check pfn_valid for the first page in
* the block.
*/
start_pfn = zone->zone_start_pfn;
end_pfn = zone_end_pfn(zone);
start_pfn = roundup(start_pfn, pageblock_nr_pages);
reserve = roundup(min_wmark_pages(zone), pageblock_nr_pages) >>
pageblock_order;

/*
* Reserve blocks are generally in place to help high-order atomic
* allocations that are short-lived. A min_free_kbytes value that
* would result in more than 2 reserve blocks for atomic allocations
* is assumed to be in place to help anti-fragmentation for the
* future allocation of hugepages at runtime.
*/
reserve = min(2, reserve);
old_reserve = zone->nr_migrate_reserve_block;

/* When memory hot-add, we almost always need to do nothing */
if (reserve == old_reserve)
return;
zone->nr_migrate_reserve_block = reserve;

for (pfn = start_pfn; pfn < end_pfn; pfn += pageblock_nr_pages) {
if (!early_page_nid_uninitialised(pfn, zone_to_nid(zone)))
return;

if (!pfn_valid(pfn))
continue;
page = pfn_to_page(pfn);

/* Watch out for overlapping nodes */
if (page_to_nid(page) != zone_to_nid(zone))
continue;

block_migratetype = get_pageblock_migratetype(page);

/* Only test what is necessary when the reserves are not met */
if (reserve > 0) {
/*
* Blocks with reserved pages will never free, skip
* them.
*/
block_end_pfn = min(pfn + pageblock_nr_pages, end_pfn);
if (pageblock_is_reserved(pfn, block_end_pfn))
continue;

/* If this block is reserved, account for it */
if (block_migratetype == MIGRATE_RESERVE) {
reserve--;
continue;
}

/* Suitable for reserving if this block is movable */
if (block_migratetype == MIGRATE_MOVABLE) {
set_pageblock_migratetype(page,
MIGRATE_RESERVE);
move_freepages_block(zone, page,
MIGRATE_RESERVE);
reserve--;
continue;
}
} else if (!old_reserve) {
/*
* At boot time we don't need to scan the whole zone
* for turning off MIGRATE_RESERVE.
*/
break;
}

/*
* If the reserve is met and this is a previous reserved block,
* take it back
*/
if (block_migratetype == MIGRATE_RESERVE) {
set_pageblock_migratetype(page, MIGRATE_MOVABLE);
move_freepages_block(zone, page, MIGRATE_MOVABLE);
}
}
}

/*
* Initially all pages are reserved - free ones are freed
* up by free_all_bootmem() once the early boot process is
Expand Down Expand Up @@ -4455,9 +4326,7 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
* movable at startup. This will force kernel allocations
* to reserve their blocks rather than leaking throughout
* the address space during boot when many long-lived
* kernel allocations are made. Later some blocks near
* the start are marked MIGRATE_RESERVE by
* setup_zone_migrate_reserve()
* kernel allocations are made.
*
* bitmap is created for zone's valid pfn range. but memmap
* can be created for invalid pages (for alignment)
Expand Down Expand Up @@ -6018,7 +5887,6 @@ static void __setup_per_zone_wmarks(void)
high_wmark_pages(zone) - low_wmark_pages(zone) -
atomic_long_read(&zone->vm_stat[NR_ALLOC_BATCH]));

setup_zone_migrate_reserve(zone);
spin_unlock_irqrestore(&zone->lock, flags);
}

Expand Down
1 change: 0 additions & 1 deletion mm/vmstat.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -923,7 +923,6 @@ static char * const migratetype_names[MIGRATE_TYPES] = {
"Unmovable",
"Reclaimable",
"Movable",
"Reserve",
#ifdef CONFIG_CMA
"CMA",
#endif
Expand Down

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