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/*
* linux/mm/compaction.c
*
* Memory compaction for the reduction of external fragmentation. Note that
* this heavily depends upon page migration to do all the real heavy
* lifting
*
* Copyright IBM Corp. 2007-2010 Mel Gorman <mel@csn.ul.ie>
*/
#include
<linux/swap.h>
#include
<linux/migrate.h>
#include
<linux/compaction.h>
#include
<linux/mm_inline.h>
#include
<linux/backing-dev.h>
#include
<linux/sysctl.h>
#include
<linux/sysfs.h>
#include
"internal.h"
#ifdef
CONFIG_COMPACTION
static
inline
void
count_compact_event
(
enum
vm_event_item
item
)
{
count_vm_event
(
item
);
}
static
inline
void
count_compact_events
(
enum
vm_event_item
item
,
long
delta
)
{
count_vm_events
(
item
,
delta
);
}
#else
#define
count_compact_event
(
item
) do { } while (0)
#define
count_compact_events
(
item
,
delta
) do { } while (0)
#endif
#if
defined
CONFIG_COMPACTION
||
defined
CONFIG_CMA
#define
CREATE_TRACE_POINTS
#include
<trace/events/compaction.h>
static
unsigned long
release_freepages
(
struct
list_head
*
freelist
)
{
struct
page
*
page
,
*
next
;
unsigned long
count
=
0
;
list_for_each_entry_safe
(
page
,
next
,
freelist
,
lru
) {
list_del
(
&
page
->
lru
);
__free_page
(
page
);
count
++
;
}
return
count
;
}
static
void
map_pages
(
struct
list_head
*
list
)
{
struct
page
*
page
;
list_for_each_entry
(
page
,
list
,
lru
) {
arch_alloc_page
(
page
,
0
);
kernel_map_pages
(
page
,
1
,
1
);
}
}
static
inline
bool
migrate_async_suitable
(
int
migratetype
)
{
return
is_migrate_cma
(
migratetype
)
||
migratetype
==
MIGRATE_MOVABLE
;
}
#ifdef
CONFIG_COMPACTION
/* Returns true if the pageblock should be scanned for pages to isolate. */
static
inline
bool
isolation_suitable
(
struct
compact_control
*
cc
,
struct
page
*
page
)
{
if
(
cc
->
ignore_skip_hint
)
return
true;
return
!
get_pageblock_skip
(
page
);
}
/*
* This function is called to clear all cached information on pageblocks that
* should be skipped for page isolation when the migrate and free page scanner
* meet.
*/
static
void
__reset_isolation_suitable
(
struct
zone
*
zone
)
{
unsigned long
start_pfn
=
zone
->
zone_start_pfn
;
unsigned long
end_pfn
=
zone
->
zone_start_pfn
+
zone
->
spanned_pages
;
unsigned long
pfn
;
zone
->
compact_cached_migrate_pfn
=
start_pfn
;
zone
->
compact_cached_free_pfn
=
end_pfn
;
zone
->
compact_blockskip_flush
=
false;
/* Walk the zone and mark every pageblock as suitable for isolation */
for
(
pfn
=
start_pfn
;
pfn
<
end_pfn
;
pfn
+=
pageblock_nr_pages
) {
struct
page
*
page
;
cond_resched
();
if
(!
pfn_valid
(
pfn
))
continue
;
page
=
pfn_to_page
(
pfn
);
if
(
zone
!=
page_zone
(
page
))
continue
;
clear_pageblock_skip
(
page
);
}
}
void
reset_isolation_suitable
(
pg_data_t
*
pgdat
)
{
int
zoneid
;
for
(
zoneid
=
0
;
zoneid
<
MAX_NR_ZONES
;
zoneid
++
) {
struct
zone
*
zone
=
&
pgdat
->
node_zones
[
zoneid
];
if
(!
populated_zone
(
zone
))
continue
;
/* Only flush if a full compaction finished recently */
if
(
zone
->
compact_blockskip_flush
)
__reset_isolation_suitable
(
zone
);
}
}
/*
* If no pages were isolated then mark this pageblock to be skipped in the
* future. The information is later cleared by __reset_isolation_suitable().
*/
static
void
update_pageblock_skip
(
struct
compact_control
*
cc
,
struct
page
*
page
,
unsigned long
nr_isolated
,
bool
migrate_scanner
)
{
struct
zone
*
zone
=
cc
->
zone
;
if
(!
page
)
return
;
if
(!
nr_isolated
) {
unsigned long
pfn
=
page_to_pfn
(
page
);
set_pageblock_skip
(
page
);
/* Update where compaction should restart */
if
(
migrate_scanner
) {
if
(!
cc
->
finished_update_migrate
&&
pfn
>
zone
->
compact_cached_migrate_pfn
)
zone
->
compact_cached_migrate_pfn
=
pfn
;
}
else
{
if
(!
cc
->
finished_update_free
&&
pfn
<
zone
->
compact_cached_free_pfn
)
zone
->
compact_cached_free_pfn
=
pfn
;
}
}
}
#else
static
inline
bool
isolation_suitable
(
struct
compact_control
*
cc
,
struct
page
*
page
)
{
return
true;
}
static
void
update_pageblock_skip
(
struct
compact_control
*
cc
,
struct
page
*
page
,
unsigned long
nr_isolated
,
bool
migrate_scanner
)
{
}
#endif
/* CONFIG_COMPACTION */
static
inline
bool
should_release_lock
(
spinlock_t
*
lock
)
{
return
need_resched
()
||
spin_is_contended
(
lock
);
}
/*
* Compaction requires the taking of some coarse locks that are potentially
* very heavily contended. Check if the process needs to be scheduled or
* if the lock is contended. For async compaction, back out in the event
* if contention is severe. For sync compaction, schedule.
*
* Returns true if the lock is held.
* Returns false if the lock is released and compaction should abort
*/
static
bool
compact_checklock_irqsave
(
spinlock_t
*
lock
,
unsigned long
*
flags
,
bool
locked
,
struct
compact_control
*
cc
)
{
if
(
should_release_lock
(
lock
)) {
if
(
locked
) {
spin_unlock_irqrestore
(
lock
,
*
flags
);
locked
=
false;
}
/* async aborts if taking too long or contended */
if
(!
cc
->
sync
) {
cc
->
contended
=
true;
return
false;
}
cond_resched
();
}
if
(!
locked
)
spin_lock_irqsave
(
lock
,
*
flags
);
return
true;
}
static
inline
bool
compact_trylock_irqsave
(
spinlock_t
*
lock
,
unsigned long
*
flags
,
struct
compact_control
*
cc
)
{
return
compact_checklock_irqsave
(
lock
,
flags
, false,
cc
);
}
/* Returns true if the page is within a block suitable for migration to */
static
bool
suitable_migration_target
(
struct
page
*
page
)
{
int
migratetype
=
get_pageblock_migratetype
(
page
);
/* Don't interfere with memory hot-remove or the min_free_kbytes blocks */
if
(
migratetype
==
MIGRATE_ISOLATE
||
migratetype
==
MIGRATE_RESERVE
)
return
false;
/* If the page is a large free page, then allow migration */
if
(
PageBuddy
(
page
)
&&
page_order
(
page
) >=
pageblock_order
)
return
true;
/* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
if
(
migrate_async_suitable
(
migratetype
))
return
true;
/* Otherwise skip the block */
return
false;
}
/*
* Isolate free pages onto a private freelist. Caller must hold zone->lock.
* If @strict is true, will abort returning 0 on any invalid PFNs or non-free
* pages inside of the pageblock (even though it may still end up isolating
* some pages).
*/
static
unsigned long
isolate_freepages_block
(
struct
compact_control
*
cc
,
unsigned long
blockpfn
,
unsigned long
end_pfn
,
struct
list_head
*
freelist
,
bool
strict
)
{
int
nr_scanned
=
0
,
total_isolated
=
0
;
struct
page
*
cursor
,
*
valid_page
=
NULL
;
unsigned long
flags
;
bool
locked
=
false;
cursor
=
pfn_to_page
(
blockpfn
);
/* Isolate free pages. */
for
(;
blockpfn
<
end_pfn
;
blockpfn
++
,
cursor
++
) {
int
isolated
,
i
;
struct
page
*
page
=
cursor
;
nr_scanned
++
;
if
(!
pfn_valid_within
(
blockpfn
))
goto
isolate_fail
;
if
(!
valid_page
)
valid_page
=
page
;
if
(!
PageBuddy
(
page
))
goto
isolate_fail
;
/*
* The zone lock must be held to isolate freepages.
* Unfortunately this is a very coarse lock and can be
* heavily contended if there are parallel allocations
* or parallel compactions. For async compaction do not
* spin on the lock and we acquire the lock as late as
* possible.
*/
locked
=
compact_checklock_irqsave
(
&
cc
->
zone
->
lock
,
&
flags
,
locked
,
cc
);
if
(!
locked
)
break
;
/* Recheck this is a suitable migration target under lock */
if
(!
strict
&&
!
suitable_migration_target
(
page
))
break
;
/* Recheck this is a buddy page under lock */
if
(!
PageBuddy
(
page
))
goto
isolate_fail
;
/* Found a free page, break it into order-0 pages */
isolated
=
split_free_page
(
page
);
total_isolated
+=
isolated
;
for
(
i
=
0
;
i
<
isolated
;
i
++
) {
list_add
(
&
page
->
lru
,
freelist
);
page
++
;
}
/* If a page was split, advance to the end of it */
if
(
isolated
) {
blockpfn
+=
isolated
-
1
;
cursor
+=
isolated
-
1
;
continue
;
}
isolate_fail
:
if
(
strict
)
break
;
}
trace_mm_compaction_isolate_freepages
(
nr_scanned
,
total_isolated
);
/*
* If strict isolation is requested by CMA then check that all the
* pages requested were isolated. If there were any failures, 0 is
* returned and CMA will fail.
*/
if
(
strict
&&
blockpfn
<
end_pfn
)
total_isolated
=
0
;
if
(
locked
)
spin_unlock_irqrestore
(
&
cc
->
zone
->
lock
,
flags
);
/* Update the pageblock-skip if the whole pageblock was scanned */
if
(
blockpfn
==
end_pfn
)
update_pageblock_skip
(
cc
,
valid_page
,
total_isolated
, false);
count_compact_events
(
COMPACTFREE_SCANNED
,
nr_scanned
);
if
(
total_isolated
)
count_compact_events
(
COMPACTISOLATED
,
total_isolated
);
return
total_isolated
;
}
/**
* isolate_freepages_range() - isolate free pages.
* @start_pfn: The first PFN to start isolating.
* @end_pfn: The one-past-last PFN.
*
* Non-free pages, invalid PFNs, or zone boundaries within the
* [start_pfn, end_pfn) range are considered errors, cause function to
* undo its actions and return zero.
*
* Otherwise, function returns one-past-the-last PFN of isolated page
* (which may be greater then end_pfn if end fell in a middle of
* a free page).
*/
unsigned long
isolate_freepages_range
(
struct
compact_control
*
cc
,
unsigned long
start_pfn
,
unsigned long
end_pfn
)
{
unsigned long
isolated
,
pfn
,
block_end_pfn
;
LIST_HEAD
(
freelist
);
for
(
pfn
=
start_pfn
;
pfn
<
end_pfn
;
pfn
+=
isolated
) {
if
(!
pfn_valid
(
pfn
)
||
cc
->
zone
!=
page_zone
(
pfn_to_page
(
pfn
)))
break
;
/*
* On subsequent iterations ALIGN() is actually not needed,
* but we keep it that we not to complicate the code.
*/
block_end_pfn
=
ALIGN
(
pfn
+
1
,
pageblock_nr_pages
);
block_end_pfn
=
min
(
block_end_pfn
,
end_pfn
);
isolated
=
isolate_freepages_block
(
cc
,
pfn
,
block_end_pfn
,
&
freelist
, true);
/*
* In strict mode, isolate_freepages_block() returns 0 if
* there are any holes in the block (ie. invalid PFNs or
* non-free pages).
*/
if
(!
isolated
)
break
;
/*
* If we managed to isolate pages, it is always (1 << n) *
* pageblock_nr_pages for some non-negative n. (Max order
* page may span two pageblocks).
*/
}
/* split_free_page does not map the pages */
map_pages
(
&
freelist
);
if
(
pfn
<
end_pfn
) {
/* Loop terminated early, cleanup. */
release_freepages
(
&
freelist
);
return
0
;
}
/* We don't use freelists for anything. */
return
pfn
;
}
/* Update the number of anon and file isolated pages in the zone */
static
void
acct_isolated
(
struct
zone
*
zone
,
bool
locked
,
struct
compact_control
*
cc
)
{
struct
page
*
page
;
unsigned
int
count
[
2
]
=
{
0
, };
list_for_each_entry
(
page
,
&
cc
->
migratepages
,
lru
)
count
[!!
page_is_file_cache
(
page
)]
++
;
/* If locked we can use the interrupt unsafe versions */
if
(
locked
) {
__mod_zone_page_state
(
zone
,
NR_ISOLATED_ANON
,
count
[
0
]);
__mod_zone_page_state
(
zone
,
NR_ISOLATED_FILE
,
count
[
1
]);
}
else
{
mod_zone_page_state
(
zone
,
NR_ISOLATED_ANON
,
count
[
0
]);
mod_zone_page_state
(
zone
,
NR_ISOLATED_FILE
,
count
[
1
]);
}
}
/* Similar to reclaim, but different enough that they don't share logic */
static
bool
too_many_isolated
(
struct
zone
*
zone
)
{
unsigned long
active
,
inactive
,
isolated
;
inactive
=
zone_page_state
(
zone
,
NR_INACTIVE_FILE
)
+
zone_page_state
(
zone
,
NR_INACTIVE_ANON
);
active
=
zone_page_state
(
zone
,
NR_ACTIVE_FILE
)
+
zone_page_state
(
zone
,
NR_ACTIVE_ANON
);
isolated
=
zone_page_state
(
zone
,
NR_ISOLATED_FILE
)
+
zone_page_state
(
zone
,
NR_ISOLATED_ANON
);
return
isolated
>
(
inactive
+
active
) /
2
;
}
/**
* isolate_migratepages_range() - isolate all migrate-able pages in range.
* @zone: Zone pages are in.
* @cc: Compaction control structure.
* @low_pfn: The first PFN of the range.
* @end_pfn: The one-past-the-last PFN of the range.
* @unevictable: true if it allows to isolate unevictable pages
*
* Isolate all pages that can be migrated from the range specified by
* [low_pfn, end_pfn). Returns zero if there is a fatal signal
* pending), otherwise PFN of the first page that was not scanned
* (which may be both less, equal to or more then end_pfn).
*
* Assumes that cc->migratepages is empty and cc->nr_migratepages is
* zero.
*
* Apart from cc->migratepages and cc->nr_migratetypes this function
* does not modify any cc's fields, in particular it does not modify
* (or read for that matter) cc->migrate_pfn.
*/
unsigned long
isolate_migratepages_range
(
struct
zone
*
zone
,
struct
compact_control
*
cc
,
unsigned long
low_pfn
,
unsigned long
end_pfn
,
bool
unevictable
)
{
unsigned long
last_pageblock_nr
=
0
,
pageblock_nr
;
unsigned long
nr_scanned
=
0
,
nr_isolated
=
0
;
struct
list_head
*
migratelist
=
&
cc
->
migratepages
;
isolate_mode_t
mode
=
0
;
unsigned long
flags
;
bool
locked
=
false;
struct
page
*
page
=
NULL
,
*
valid_page
=
NULL
;
/*
* Ensure that there are not too many pages isolated from the LRU
* list by either parallel reclaimers or compaction. If there are,
* delay for some time until fewer pages are isolated
*/
while
(
unlikely
(
too_many_isolated
(
zone
))) {
/* async migration should just abort */
if
(!
cc
->
sync
)
return
0
;
congestion_wait
(
BLK_RW_ASYNC
,
HZ
/
10
);
if
(
fatal_signal_pending
(
current
))
return
0
;
}
/* Time to isolate some pages for migration */
cond_resched
();
for
(;
low_pfn
<
end_pfn
;
low_pfn
++
) {
/* give a chance to irqs before checking need_resched() */
if
(
locked
&&
!((
low_pfn
+
1
) %
SWAP_CLUSTER_MAX
)) {
if
(
should_release_lock
(
&
zone
->
lru_lock
)) {
spin_unlock_irqrestore
(
&
zone
->
lru_lock
,
flags
);
locked
=
false;
}
}
/*
* migrate_pfn does not necessarily start aligned to a
* pageblock. Ensure that pfn_valid is called when moving
* into a new MAX_ORDER_NR_PAGES range in case of large
* memory holes within the zone
*/
if
((
low_pfn
&
(
MAX_ORDER_NR_PAGES
-
1
))
==
0
) {
if
(!
pfn_valid
(
low_pfn
)) {
low_pfn
+=
MAX_ORDER_NR_PAGES
-
1
;
continue
;
}
}
if
(!
pfn_valid_within
(
low_pfn
))
continue
;
nr_scanned
++
;
/*
* Get the page and ensure the page is within the same zone.
* See the comment in isolate_freepages about overlapping
* nodes. It is deliberate that the new zone lock is not taken
* as memory compaction should not move pages between nodes.
*/
page
=
pfn_to_page
(
low_pfn
);
if
(
page_zone
(
page
)
!=
zone
)
continue
;
if
(!
valid_page
)
valid_page
=
page
;
/* If isolation recently failed, do not retry */
pageblock_nr
=
low_pfn
>>
pageblock_order
;
if
(!
isolation_suitable
(
cc
,
page
))
goto
next_pageblock
;
/* Skip if free */
if
(
PageBuddy
(
page
))
continue
;
/*
* For async migration, also only scan in MOVABLE blocks. Async
* migration is optimistic to see if the minimum amount of work
* satisfies the allocation
*/
if
(!
cc
->
sync
&&
last_pageblock_nr
!=
pageblock_nr
&&
!
migrate_async_suitable
(
get_pageblock_migratetype
(
page
))) {
cc
->
finished_update_migrate
=
true;
goto
next_pageblock
;
}
/* Check may be lockless but that's ok as we recheck later */
if
(!
PageLRU
(
page
))
continue
;
/*
* PageLRU is set. lru_lock normally excludes isolation
* splitting and collapsing (collapsing has already happened
* if PageLRU is set) but the lock is not necessarily taken
* here and it is wasteful to take it just to check transhuge.
* Check TransHuge without lock and skip the whole pageblock if
* it's either a transhuge or hugetlbfs page, as calling
* compound_order() without preventing THP from splitting the
* page underneath us may return surprising results.
*/
if
(
PageTransHuge
(
page
)) {
if
(!
locked
)
goto
next_pageblock
;
low_pfn
+=
(
1
<<
compound_order
(
page
))
-
1
;
continue
;
}
/* Check if it is ok to still hold the lock */
locked
=
compact_checklock_irqsave
(
&
zone
->
lru_lock
,
&
flags
,
locked
,
cc
);
if
(!
locked
||
fatal_signal_pending
(
current
))
break
;
/* Recheck PageLRU and PageTransHuge under lock */
if
(!
PageLRU
(
page
))
continue
;
if
(
PageTransHuge
(
page
)) {
low_pfn
+=
(
1
<<
compound_order
(
page
))
-
1
;
continue
;
}
if
(!
cc
->
sync
)
mode
|=
ISOLATE_ASYNC_MIGRATE
;
if
(
unevictable
)
mode
|=
ISOLATE_UNEVICTABLE
;
/* Try isolate the page */
if
(
__isolate_lru_page
(
page
,
mode
)
!=
0
)
continue
;
VM_BUG_ON
(
PageTransCompound
(
page
));
/* Successfully isolated */
cc
->
finished_update_migrate
=
true;
del_page_from_lru_list
(
zone
,
page
,
page_lru
(
page
));
list_add
(
&
page
->
lru
,
migratelist
);
cc
->
nr_migratepages
++
;
nr_isolated
++
;
/* Avoid isolating too much */
if
(
cc
->
nr_migratepages
==
COMPACT_CLUSTER_MAX
) {
++
low_pfn
;
break
;
}
continue
;
next_pageblock
:
low_pfn
+=
pageblock_nr_pages
;
low_pfn
=
ALIGN
(
low_pfn
,
pageblock_nr_pages
)
-
1
;
last_pageblock_nr
=
pageblock_nr
;
}
acct_isolated
(
zone
,
locked
,
cc
);
if
(
locked
)
spin_unlock_irqrestore
(
&
zone
->
lru_lock
,
flags
);
/* Update the pageblock-skip if the whole pageblock was scanned */
if
(
low_pfn
==
end_pfn
)
update_pageblock_skip
(
cc
,
valid_page
,
nr_isolated
, true);
trace_mm_compaction_isolate_migratepages
(
nr_scanned
,
nr_isolated
);
count_compact_events
(
COMPACTMIGRATE_SCANNED
,
nr_scanned
);
if
(
nr_isolated
)
count_compact_events
(
COMPACTISOLATED
,
nr_isolated
);
return
low_pfn
;
}
#endif
/* CONFIG_COMPACTION || CONFIG_CMA */
#ifdef
CONFIG_COMPACTION
/*
* Based on information in the current compact_control, find blocks
* suitable for isolating free pages from and then isolate them.
*/
static
void
isolate_freepages
(
struct
zone
*
zone
,
struct
compact_control
*
cc
)
{
struct
page
*
page
;
unsigned long
high_pfn
,
low_pfn
,
pfn
,
zone_end_pfn
,
end_pfn
;
int
nr_freepages
=
cc
->
nr_freepages
;
struct
list_head
*
freelist
=
&
cc
->
freepages
;
/*
* Initialise the free scanner. The starting point is where we last
* scanned from (or the end of the zone if starting). The low point
* is the end of the pageblock the migration scanner is using.
*/
pfn
=
cc
->
free_pfn
;
low_pfn
=
cc
->
migrate_pfn
+
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.
*/
high_pfn
=
min
(
low_pfn
,
pfn
);
zone_end_pfn
=
zone
->
zone_start_pfn
+
zone
->
spanned_pages
;
/*
* 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
) {
unsigned long
isolated
;
if
(!
pfn_valid
(
pfn
))
continue
;
/*
* Check for overlapping nodes/zones. It's possible on some
* configurations to have a setup like
* node0 node1 node0
* 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
);
if
(
page_zone
(
page
)
!=
zone
)
continue
;
/* Check the block is suitable for migration */
if
(!
suitable_migration_target
(
page
))
continue
;
/* If isolation recently failed, do not retry */
if
(!
isolation_suitable
(
cc
,
page
))
continue
;
/* Found a block suitable for isolating free pages from */
isolated
=
0
;
/*
* As pfn may not start aligned, pfn+pageblock_nr_page
* may cross a MAX_ORDER_NR_PAGES boundary and miss
* a pfn_valid check. Ensure isolate_freepages_block()
* only scans within a pageblock
*/
end_pfn
=
ALIGN
(
pfn
+
1
,
pageblock_nr_pages
);
end_pfn
=
min
(
end_pfn
,
zone_end_pfn
);
isolated
=
isolate_freepages_block
(
cc
,
pfn
,
end_pfn
,
freelist
, false);
nr_freepages
+=
isolated
;
/*
* Record the highest PFN we isolated pages from. When next
* looking for free pages, the search will restart here as
* page migration may have returned some pages to the allocator
*/
if
(
isolated
) {
cc
->
finished_update_free
=
true;
high_pfn
=
max
(
high_pfn
,
pfn
);
}
}
/* split_free_page does not map the pages */
map_pages
(
freelist
);
cc
->
free_pfn
=
high_pfn
;
cc
->
nr_freepages
=
nr_freepages
;
}
/*
* This is a migrate-callback that "allocates" freepages by taking pages
* from the isolated freelists in the block we are migrating to.
*/
static
struct
page
*
compaction_alloc
(
struct
page
*
migratepage
,
unsigned long
data
,
int
*
*
result
)
{
struct
compact_control
*
cc
=
(
struct
compact_control
*
)
data
;
struct
page
*
freepage
;
/* Isolate free pages if necessary */
if
(
list_empty
(
&
cc
->
freepages
)) {
isolate_freepages
(
cc
->
zone
,
cc
);
if
(
list_empty
(
&
cc
->
freepages
))
return
NULL
;
}
freepage
=
list_entry
(
cc
->
freepages
.
next
,
struct
page
,
lru
);
list_del
(
&
freepage
->
lru
);
cc
->
nr_freepages
--
;
return
freepage
;
}
/*
* We cannot control nr_migratepages and nr_freepages fully when migration is
* running as migrate_pages() has no knowledge of compact_control. When
* migration is complete, we count the number of pages on the lists by hand.
*/
static
void
update_nr_listpages
(
struct
compact_control
*
cc
)
{
int
nr_migratepages
=
0
;
int
nr_freepages
=
0
;
struct
page
*
page
;
list_for_each_entry
(
page
,
&
cc
->
migratepages
,
lru
)
nr_migratepages
++
;
list_for_each_entry
(
page
,
&
cc
->
freepages
,
lru
)
nr_freepages
++
;
cc
->
nr_migratepages
=
nr_migratepages
;
cc
->
nr_freepages
=
nr_freepages
;
}
/* possible outcome of isolate_migratepages */
typedef
enum
{
ISOLATE_ABORT
,
/* Abort compaction now */
ISOLATE_NONE
,
/* No pages isolated, continue scanning */
ISOLATE_SUCCESS
,
/* Pages isolated, migrate */
}
isolate_migrate_t
;
/*
* Isolate all pages that can be migrated from the block pointed to by
* the migrate scanner within compact_control.
*/
static
isolate_migrate_t
isolate_migratepages
(
struct
zone
*
zone
,
struct
compact_control
*
cc
)
{
unsigned long
low_pfn
,
end_pfn
;
/* Do not scan outside zone boundaries */
low_pfn
=
max
(
cc
->
migrate_pfn
,
zone
->
zone_start_pfn
);
/* Only scan within a pageblock boundary */
end_pfn
=
ALIGN
(
low_pfn
+
pageblock_nr_pages
,
pageblock_nr_pages
);
/* Do not cross the free scanner or scan within a memory hole */
if
(
end_pfn
>
cc
->
free_pfn
||
!
pfn_valid
(
low_pfn
)) {
cc
->
migrate_pfn
=
end_pfn
;
return
ISOLATE_NONE
;
}
/* Perform the isolation */
low_pfn
=
isolate_migratepages_range
(
zone
,
cc
,
low_pfn
,
end_pfn
, false);
if
(!
low_pfn
||
cc
->
contended
)
return
ISOLATE_ABORT
;
cc
->
migrate_pfn
=
low_pfn
;
return
ISOLATE_SUCCESS
;
}
static
int
compact_finished
(
struct
zone
*
zone
,
struct
compact_control
*
cc
)
{
unsigned
int
order
;
unsigned long
watermark
;
if
(
fatal_signal_pending
(
current
))
return
COMPACT_PARTIAL
;
/* Compaction run completes if the migrate and free scanner meet */
if
(
cc
->
free_pfn
<=
cc
->
migrate_pfn
) {
/*
* Mark that the PG_migrate_skip information should be cleared
* by kswapd when it goes to sleep. kswapd does not set the
* flag itself as the decision to be clear should be directly
* based on an allocation request.
*/
if
(!
current_is_kswapd
())
zone
->
compact_blockskip_flush
=
true;
return
COMPACT_COMPLETE
;
}
/*
* order == -1 is expected when compacting via
* /proc/sys/vm/compact_memory
*/
if
(
cc
->
order
==
-1
)
return
COMPACT_CONTINUE
;
/* Compaction run is not finished if the watermark is not met */
watermark
=
low_wmark_pages
(
zone
);
watermark
+=
(
1
<<
cc
->
order
);
if
(!
zone_watermark_ok
(
zone
,
cc
->
order
,
watermark
,
0
,
0
))
return
COMPACT_CONTINUE
;
/* Direct compactor: Is a suitable page free? */
for
(
order
=
cc
->
order
;
order
<
MAX_ORDER
;
order
++
) {
struct
free_area
*
area
=
&
zone
->
free_area
[
order
];
/* Job done if page is free of the right migratetype */
if
(!
list_empty
(
&
area
->
free_list
[
cc
->
migratetype
]))
return
COMPACT_PARTIAL
;
/* Job done if allocation would set block type */
if
(
cc
->
order
>=
pageblock_order
&&
area
->
nr_free
)
return
COMPACT_PARTIAL
;
}
return
COMPACT_CONTINUE
;
}
/*
* compaction_suitable: Is this suitable to run compaction on this zone now?
* Returns
* COMPACT_SKIPPED - If there are too few free pages for compaction
* COMPACT_PARTIAL - If the allocation would succeed without compaction
* COMPACT_CONTINUE - If compaction should run now
*/
unsigned long
compaction_suitable
(
struct
zone
*
zone
,
int
order
)
{
int
fragindex
;
unsigned long
watermark
;
/*
* order == -1 is expected when compacting via
* /proc/sys/vm/compact_memory
*/
if
(
order
==
-1
)
return
COMPACT_CONTINUE
;
/*
* Watermarks for order-0 must be met for compaction. Note the 2UL.
* This is because during migration, copies of pages need to be
* allocated and for a short time, the footprint is higher
*/
watermark
=
low_wmark_pages
(
zone
)
+
(
2UL
<<
order
);
if
(!
zone_watermark_ok
(
zone
,
0
,
watermark
,
0
,
0
))
return
COMPACT_SKIPPED
;
/*
* fragmentation index determines if allocation failures are due to
* low memory or external fragmentation
*
* index of -1000 implies allocations might succeed depending on
* watermarks
* index towards 0 implies failure is due to lack of memory
* index towards 1000 implies failure is due to fragmentation
*
* Only compact if a failure would be due to fragmentation.
*/
fragindex
=
fragmentation_index
(
zone
,
order
);
if
(
fragindex
>=
0
&&
fragindex
<=
sysctl_extfrag_threshold
)
return
COMPACT_SKIPPED
;
if
(
fragindex
==
-1000
&&
zone_watermark_ok
(
zone
,
order
,
watermark
,
0
,
0
))
return
COMPACT_PARTIAL
;
return
COMPACT_CONTINUE
;
}
static
int
compact_zone
(
struct
zone
*
zone
,
struct
compact_control
*
cc
)
{
int
ret
;
unsigned long
start_pfn
=
zone
->
zone_start_pfn
;
unsigned long
end_pfn
=
zone
->
zone_start_pfn
+
zone
->
spanned_pages
;
ret
=
compaction_suitable
(
zone
,
cc
->
order
);
switch
(
ret
) {
case
COMPACT_PARTIAL
:
case
COMPACT_SKIPPED
:
/* Compaction is likely to fail */
return
ret
;
case
COMPACT_CONTINUE
:
/* Fall through to compaction */
;
}
/*
* Setup to move all movable pages to the end of the zone. Used cached
* information on where the scanners should start but check that it
* is initialised by ensuring the values are within zone boundaries.
*/
cc
->
migrate_pfn
=
zone
->
compact_cached_migrate_pfn
;
cc
->
free_pfn
=
zone
->
compact_cached_free_pfn
;
if
(
cc
->
free_pfn
<
start_pfn
||
cc
->
free_pfn
>
end_pfn
) {
cc
->
free_pfn
=
end_pfn
&
~(
pageblock_nr_pages
-
1
);
zone
->
compact_cached_free_pfn
=
cc
->
free_pfn
;
}
if
(
cc
->
migrate_pfn
<
start_pfn
||
cc
->
migrate_pfn
>
end_pfn
) {
cc
->
migrate_pfn
=
start_pfn
;
zone
->
compact_cached_migrate_pfn
=
cc
->
migrate_pfn
;
}
/*
* Clear pageblock skip if there were failures recently and compaction
* is about to be retried after being deferred. kswapd does not do
* this reset as it'll reset the cached information when going to sleep.
*/
if
(
compaction_restarting
(
zone
,
cc
->
order
)
&&
!
current_is_kswapd
())
__reset_isolation_suitable
(
zone
);
migrate_prep_local
();
while
((
ret
=
compact_finished
(
zone
,
cc
))
==
COMPACT_CONTINUE
) {
unsigned long
nr_migrate
,
nr_remaining
;
int
err
;
switch
(
isolate_migratepages
(
zone
,
cc
)) {
case
ISOLATE_ABORT
:
ret
=
COMPACT_PARTIAL
;
putback_lru_pages
(
&
cc
->
migratepages
);
cc
->
nr_migratepages
=
0
;
goto
out
;
case
ISOLATE_NONE
:
continue
;
case
ISOLATE_SUCCESS
:
;
}
nr_migrate
=
cc
->
nr_migratepages
;
err
=
migrate_pages
(
&
cc
->
migratepages
,
compaction_alloc
,
(
unsigned long
)
cc
, false,
cc
->
sync
?
MIGRATE_SYNC_LIGHT
:
MIGRATE_ASYNC
);
update_nr_listpages
(
cc
);
nr_remaining
=
cc
->
nr_migratepages
;
trace_mm_compaction_migratepages
(
nr_migrate
-
nr_remaining
,
nr_remaining
);
/* Release LRU pages not migrated */
if
(
err
) {
putback_lru_pages
(
&
cc
->
migratepages
);
cc
->
nr_migratepages
=
0
;
if
(
err
==
-
ENOMEM
) {
ret
=
COMPACT_PARTIAL
;
goto
out
;
}
}
}
out
:
/* Release free pages and check accounting */
cc
->
nr_freepages
-=
release_freepages
(
&
cc
->
freepages
);
VM_BUG_ON
(
cc
->
nr_freepages
!=
0
);
return
ret
;
}
static
unsigned long
compact_zone_order
(
struct
zone
*
zone
,
int
order
,
gfp_t
gfp_mask
,
bool
sync
,
bool
*
contended
)
{
unsigned long
ret
;
struct
compact_control
cc
=
{
.
nr_freepages
=
0
,
.
nr_migratepages
=
0
,
.
order
=
order
,
.
migratetype
=
allocflags_to_migratetype
(
gfp_mask
),
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