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/*
* linux/mm/swap.c
*
* Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
*/
/*
* This file contains the default values for the operation of the
* Linux VM subsystem. Fine-tuning documentation can be found in
* Documentation/sysctl/vm.txt.
* Started 18.12.91
* Swap aging added 23.2.95, Stephen Tweedie.
* Buffermem limits added 12.3.98, Rik van Riel.
*/
#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/kernel_stat.h>
#include <linux/swap.h>
#include <linux/mman.h>
#include <linux/pagemap.h>
#include <linux/pagevec.h>
#include <linux/init.h>
#include <linux/export.h>
#include <linux/mm_inline.h>
#include <linux/percpu_counter.h>
#include <linux/percpu.h>
#include <linux/cpu.h>
#include <linux/notifier.h>
#include <linux/backing-dev.h>
#include <linux/memcontrol.h>
#include <linux/gfp.h>
#include "internal.h"
/* How many pages do we try to swap or page in/out together? */
int page_cluster;
static DEFINE_PER_CPU(struct pagevec[NR_LRU_LISTS], lru_add_pvecs);
static DEFINE_PER_CPU(struct pagevec, lru_rotate_pvecs);
static DEFINE_PER_CPU(struct pagevec, lru_deactivate_pvecs);
/*
* This path almost never happens for VM activity - pages are normally
* freed via pagevecs. But it gets used by networking.
*/
static void __page_cache_release(struct page *page)
{
if (PageLRU(page)) {
struct zone *zone = page_zone(page);
struct lruvec *lruvec;
unsigned long flags;
spin_lock_irqsave(&zone->lru_lock, flags);
lruvec = mem_cgroup_page_lruvec(page, zone);
VM_BUG_ON(!PageLRU(page));
__ClearPageLRU(page);
del_page_from_lru_list(page, lruvec, page_off_lru(page));
spin_unlock_irqrestore(&zone->lru_lock, flags);
}
}
static void __put_single_page(struct page *page)
{
__page_cache_release(page);
free_hot_cold_page(page, 0);
}
static void __put_compound_page(struct page *page)
{
compound_page_dtor *dtor;
__page_cache_release(page);
dtor = get_compound_page_dtor(page);
(*dtor)(page);
}
static void put_compound_page(struct page *page)
{
if (unlikely(PageTail(page))) {
/* __split_huge_page_refcount can run under us */
struct page *page_head = compound_trans_head(page);
if (likely(page != page_head &&
get_page_unless_zero(page_head))) {
unsigned long flags;
/*
* THP can not break up slab pages so avoid taking
* compound_lock(). Slab performs non-atomic bit ops
* on page->flags for better performance. In particular
* slab_unlock() in slub used to be a hot path. It is
* still hot on arches that do not support
* this_cpu_cmpxchg_double().
*/
if (PageSlab(page_head)) {
if (PageTail(page)) {
if (put_page_testzero(page_head))
VM_BUG_ON(1);
atomic_dec(&page->_mapcount);
goto skip_lock_tail;
} else
goto skip_lock;
}
/*
* page_head wasn't a dangling pointer but it
* may not be a head page anymore by the time
* we obtain the lock. That is ok as long as it
* can't be freed from under us.
*/
flags = compound_lock_irqsave(page_head);
if (unlikely(!PageTail(page))) {
/* __split_huge_page_refcount run before us */
compound_unlock_irqrestore(page_head, flags);
skip_lock:
if (put_page_testzero(page_head))
__put_single_page(page_head);
out_put_single:
if (put_page_testzero(page))
__put_single_page(page);
return;
}
VM_BUG_ON(page_head != page->first_page);
/*
* We can release the refcount taken by
* get_page_unless_zero() now that
* __split_huge_page_refcount() is blocked on
* the compound_lock.
*/
if (put_page_testzero(page_head))
VM_BUG_ON(1);
/* __split_huge_page_refcount will wait now */
VM_BUG_ON(page_mapcount(page) <= 0);
atomic_dec(&page->_mapcount);
VM_BUG_ON(atomic_read(&page_head->_count) <= 0);
VM_BUG_ON(atomic_read(&page->_count) != 0);
compound_unlock_irqrestore(page_head, flags);
skip_lock_tail:
if (put_page_testzero(page_head)) {
if (PageHead(page_head))
__put_compound_page(page_head);
else
__put_single_page(page_head);
}
} else {
/* page_head is a dangling pointer */
VM_BUG_ON(PageTail(page));
goto out_put_single;
}
} else if (put_page_testzero(page)) {
if (PageHead(page))
__put_compound_page(page);
else
__put_single_page(page);
}
}
void put_page(struct page *page)
{
if (unlikely(PageCompound(page)))
put_compound_page(page);
else if (put_page_testzero(page))
__put_single_page(page);
}
EXPORT_SYMBOL(put_page);
/*
* This function is exported but must not be called by anything other
* than get_page(). It implements the slow path of get_page().
*/
bool __get_page_tail(struct page *page)
{
/*
* This takes care of get_page() if run on a tail page
* returned by one of the get_user_pages/follow_page variants.
* get_user_pages/follow_page itself doesn't need the compound
* lock because it runs __get_page_tail_foll() under the
* proper PT lock that already serializes against
* split_huge_page().
*/
unsigned long flags;
bool got = false;
struct page *page_head = compound_trans_head(page);
if (likely(page != page_head && get_page_unless_zero(page_head))) {
/* Ref to put_compound_page() comment. */
if (PageSlab(page_head)) {
if (likely(PageTail(page))) {
__get_page_tail_foll(page, false);
return true;
} else {
put_page(page_head);
return false;
}
}
/*
* page_head wasn't a dangling pointer but it
* may not be a head page anymore by the time
* we obtain the lock. That is ok as long as it
* can't be freed from under us.
*/
flags = compound_lock_irqsave(page_head);
/* here __split_huge_page_refcount won't run anymore */
if (likely(PageTail(page))) {
__get_page_tail_foll(page, false);
got = true;
}
compound_unlock_irqrestore(page_head, flags);
if (unlikely(!got))
put_page(page_head);
}
return got;
}
EXPORT_SYMBOL(__get_page_tail);
/**
* put_pages_list() - release a list of pages
* @pages: list of pages threaded on page->lru
*
* Release a list of pages which are strung together on page.lru. Currently
* used by read_cache_pages() and related error recovery code.
*/
void put_pages_list(struct list_head *pages)
{
while (!list_empty(pages)) {
struct page *victim;
victim = list_entry(pages->prev, struct page, lru);
list_del(&victim->lru);
page_cache_release(victim);
}
}
EXPORT_SYMBOL(put_pages_list);
/*
* get_kernel_pages() - pin kernel pages in memory
* @kiov: An array of struct kvec structures
* @nr_segs: number of segments to pin
* @write: pinning for read/write, currently ignored
* @pages: array that receives pointers to the pages pinned.
* Should be at least nr_segs long.
*
* Returns number of pages pinned. This may be fewer than the number
* requested. If nr_pages is 0 or negative, returns 0. If no pages
* were pinned, returns -errno. Each page returned must be released
* with a put_page() call when it is finished with.
*/
int get_kernel_pages(const struct kvec *kiov, int nr_segs, int write,
struct page **pages)
{
int seg;
for (seg = 0; seg < nr_segs; seg++) {
if (WARN_ON(kiov[seg].iov_len != PAGE_SIZE))
return seg;
pages[seg] = kmap_to_page(kiov[seg].iov_base);
page_cache_get(pages[seg]);
}
return seg;
}
EXPORT_SYMBOL_GPL(get_kernel_pages);
/*
* get_kernel_page() - pin a kernel page in memory
* @start: starting kernel address
* @write: pinning for read/write, currently ignored
* @pages: array that receives pointer to the page pinned.
* Must be at least nr_segs long.
*
* Returns 1 if page is pinned. If the page was not pinned, returns
* -errno. The page returned must be released with a put_page() call
* when it is finished with.
*/
int get_kernel_page(unsigned long start, int write, struct page **pages)
{
const struct kvec kiov = {
.iov_base = (void *)start,
.iov_len = PAGE_SIZE
};
return get_kernel_pages(&kiov, 1, write, pages);
}
EXPORT_SYMBOL_GPL(get_kernel_page);
static void pagevec_lru_move_fn(struct pagevec *pvec,
void (*move_fn)(struct page *page, struct lruvec *lruvec, void *arg),
void *arg)
{
int i;
struct zone *zone = NULL;
struct lruvec *lruvec;
unsigned long flags = 0;
for (i = 0; i < pagevec_count(pvec); i++) {
struct page *page = pvec->pages[i];
struct zone *pagezone = page_zone(page);
if (pagezone != zone) {
if (zone)
spin_unlock_irqrestore(&zone->lru_lock, flags);
zone = pagezone;
spin_lock_irqsave(&zone->lru_lock, flags);
}
lruvec = mem_cgroup_page_lruvec(page, zone);
(*move_fn)(page, lruvec, arg);
}
if (zone)
spin_unlock_irqrestore(&zone->lru_lock, flags);
release_pages(pvec->pages, pvec->nr, pvec->cold);
pagevec_reinit(pvec);
}
static void pagevec_move_tail_fn(struct page *page, struct lruvec *lruvec,
void *arg)
{
int *pgmoved = arg;
if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
enum lru_list lru = page_lru_base_type(page);
list_move_tail(&page->lru, &lruvec->lists[lru]);
(*pgmoved)++;
}
}
/*
* pagevec_move_tail() must be called with IRQ disabled.
* Otherwise this may cause nasty races.
*/
static void pagevec_move_tail(struct pagevec *pvec)
{
int pgmoved = 0;
pagevec_lru_move_fn(pvec, pagevec_move_tail_fn, &pgmoved);
__count_vm_events(PGROTATED, pgmoved);
}
/*
* Writeback is about to end against a page which has been marked for immediate
* reclaim. If it still appears to be reclaimable, move it to the tail of the
* inactive list.
*/
void rotate_reclaimable_page(struct page *page)
{
if (!PageLocked(page) && !PageDirty(page) && !PageActive(page) &&
!PageUnevictable(page) && PageLRU(page)) {
struct pagevec *pvec;
unsigned long flags;
page_cache_get(page);
local_irq_save(flags);
pvec = &__get_cpu_var(lru_rotate_pvecs);
if (!pagevec_add(pvec, page))
pagevec_move_tail(pvec);
local_irq_restore(flags);
}
}
static void update_page_reclaim_stat(struct lruvec *lruvec,
int file, int rotated)
{
struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
reclaim_stat->recent_scanned[file]++;
if (rotated)
reclaim_stat->recent_rotated[file]++;
}
static void __activate_page(struct page *page, struct lruvec *lruvec,
void *arg)
{
if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
int file = page_is_file_cache(page);
int lru = page_lru_base_type(page);
del_page_from_lru_list(page, lruvec, lru);
SetPageActive(page);
lru += LRU_ACTIVE;
add_page_to_lru_list(page, lruvec, lru);
__count_vm_event(PGACTIVATE);
update_page_reclaim_stat(lruvec, file, 1);
}
}
#ifdef CONFIG_SMP
static DEFINE_PER_CPU(struct pagevec, activate_page_pvecs);
static void activate_page_drain(int cpu)
{
struct pagevec *pvec = &per_cpu(activate_page_pvecs, cpu);
if (pagevec_count(pvec))
pagevec_lru_move_fn(pvec, __activate_page, NULL);
}
void activate_page(struct page *page)
{
if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
struct pagevec *pvec = &get_cpu_var(activate_page_pvecs);
page_cache_get(page);
if (!pagevec_add(pvec, page))
pagevec_lru_move_fn(pvec, __activate_page, NULL);
put_cpu_var(activate_page_pvecs);
}
}
#else
static inline void activate_page_drain(int cpu)
{
}
void activate_page(struct page *page)
{
struct zone *zone = page_zone(page);
spin_lock_irq(&zone->lru_lock);
__activate_page(page, mem_cgroup_page_lruvec(page, zone), NULL);
spin_unlock_irq(&zone->lru_lock);
}
#endif
/*
* Mark a page as having seen activity.
*
* inactive,unreferenced -> inactive,referenced
* inactive,referenced -> active,unreferenced
* active,unreferenced -> active,referenced
*/
void mark_page_accessed(struct page *page)
{
if (!PageActive(page) && !PageUnevictable(page) &&
PageReferenced(page) && PageLRU(page)) {
activate_page(page);
ClearPageReferenced(page);
} else if (!PageReferenced(page)) {
SetPageReferenced(page);
}
}
EXPORT_SYMBOL(mark_page_accessed);
void __lru_cache_add(struct page *page, enum lru_list lru)
{
struct pagevec *pvec = &get_cpu_var(lru_add_pvecs)[lru];
page_cache_get(page);
if (!pagevec_add(pvec, page))
__pagevec_lru_add(pvec, lru);
put_cpu_var(lru_add_pvecs);
}
EXPORT_SYMBOL(__lru_cache_add);
/**
* lru_cache_add_lru - add a page to a page list
* @page: the page to be added to the LRU.
* @lru: the LRU list to which the page is added.
*/
void lru_cache_add_lru(struct page *page, enum lru_list lru)
{
if (PageActive(page)) {
VM_BUG_ON(PageUnevictable(page));
ClearPageActive(page);
} else if (PageUnevictable(page)) {
VM_BUG_ON(PageActive(page));
ClearPageUnevictable(page);
}
VM_BUG_ON(PageLRU(page) || PageActive(page) || PageUnevictable(page));
__lru_cache_add(page, lru);
}
/**
* add_page_to_unevictable_list - add a page to the unevictable list
* @page: the page to be added to the unevictable list
*
* Add page directly to its zone's unevictable list. To avoid races with
* tasks that might be making the page evictable, through eg. munlock,
* munmap or exit, while it's not on the lru, we want to add the page
* while it's locked or otherwise "invisible" to other tasks. This is
* difficult to do when using the pagevec cache, so bypass that.
*/
void add_page_to_unevictable_list(struct page *page)
{
struct zone *zone = page_zone(page);
struct lruvec *lruvec;
spin_lock_irq(&zone->lru_lock);
lruvec = mem_cgroup_page_lruvec(page, zone);
SetPageUnevictable(page);
SetPageLRU(page);
add_page_to_lru_list(page, lruvec, LRU_UNEVICTABLE);
spin_unlock_irq(&zone->lru_lock);
}
/*
* If the page can not be invalidated, it is moved to the
* inactive list to speed up its reclaim. It is moved to the
* head of the list, rather than the tail, to give the flusher
* threads some time to write it out, as this is much more
* effective than the single-page writeout from reclaim.
*
* If the page isn't page_mapped and dirty/writeback, the page
* could reclaim asap using PG_reclaim.
*
* 1. active, mapped page -> none
* 2. active, dirty/writeback page -> inactive, head, PG_reclaim
* 3. inactive, mapped page -> none
* 4. inactive, dirty/writeback page -> inactive, head, PG_reclaim
* 5. inactive, clean -> inactive, tail
* 6. Others -> none
*
* In 4, why it moves inactive's head, the VM expects the page would
* be write it out by flusher threads as this is much more effective
* than the single-page writeout from reclaim.
*/
static void lru_deactivate_fn(struct page *page, struct lruvec *lruvec,
void *arg)
{
int lru, file;
bool active;
if (!PageLRU(page))
return;
if (PageUnevictable(page))
return;
/* Some processes are using the page */
if (page_mapped(page))
return;
active = PageActive(page);
file = page_is_file_cache(page);
lru = page_lru_base_type(page);
del_page_from_lru_list(page, lruvec, lru + active);
ClearPageActive(page);
ClearPageReferenced(page);
add_page_to_lru_list(page, lruvec, lru);
if (PageWriteback(page) || PageDirty(page)) {
/*
* PG_reclaim could be raced with end_page_writeback
* It can make readahead confusing. But race window
* is _really_ small and it's non-critical problem.
*/
SetPageReclaim(page);
} else {
/*
* The page's writeback ends up during pagevec
* We moves tha page into tail of inactive.
*/
list_move_tail(&page->lru, &lruvec->lists[lru]);
__count_vm_event(PGROTATED);
}
if (active)
__count_vm_event(PGDEACTIVATE);
update_page_reclaim_stat(lruvec, file, 0);
}
/*
* Drain pages out of the cpu's pagevecs.
* Either "cpu" is the current CPU, and preemption has already been
* disabled; or "cpu" is being hot-unplugged, and is already dead.
*/
void lru_add_drain_cpu(int cpu)
{
struct pagevec *pvecs = per_cpu(lru_add_pvecs, cpu);
struct pagevec *pvec;
int lru;
for_each_lru(lru) {
pvec = &pvecs[lru - LRU_BASE];
if (pagevec_count(pvec))
__pagevec_lru_add(pvec, lru);
}
pvec = &per_cpu(lru_rotate_pvecs, cpu);
if (pagevec_count(pvec)) {
unsigned long flags;
/* No harm done if a racing interrupt already did this */
local_irq_save(flags);
pagevec_move_tail(pvec);
local_irq_restore(flags);
}
pvec = &per_cpu(lru_deactivate_pvecs, cpu);
if (pagevec_count(pvec))
pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL);
activate_page_drain(cpu);
}
/**
* deactivate_page - forcefully deactivate a page
* @page: page to deactivate
*
* This function hints the VM that @page is a good reclaim candidate,
* for example if its invalidation fails due to the page being dirty
* or under writeback.
*/
void deactivate_page(struct page *page)
{
/*
* In a workload with many unevictable page such as mprotect, unevictable
* page deactivation for accelerating reclaim is pointless.
*/
if (PageUnevictable(page))
return;
if (likely(get_page_unless_zero(page))) {
struct pagevec *pvec = &get_cpu_var(lru_deactivate_pvecs);
if (!pagevec_add(pvec, page))
pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL);
put_cpu_var(lru_deactivate_pvecs);
}
}
void lru_add_drain(void)
{
lru_add_drain_cpu(get_cpu());
put_cpu();
}
static void lru_add_drain_per_cpu(struct work_struct *dummy)
{
lru_add_drain();
}
/*
* Returns 0 for success
*/
int lru_add_drain_all(void)
{
return schedule_on_each_cpu(lru_add_drain_per_cpu);
}
/*
* Batched page_cache_release(). Decrement the reference count on all the
* passed pages. If it fell to zero then remove the page from the LRU and
* free it.
*
* Avoid taking zone->lru_lock if possible, but if it is taken, retain it
* for the remainder of the operation.
*
* The locking in this function is against shrink_inactive_list(): we recheck
* the page count inside the lock to see whether shrink_inactive_list()
* grabbed the page via the LRU. If it did, give up: shrink_inactive_list()
* will free it.
*/
void release_pages(struct page **pages, int nr, int cold)
{
int i;
LIST_HEAD(pages_to_free);
struct zone *zone = NULL;
struct lruvec *lruvec;
unsigned long uninitialized_var(flags);
for (i = 0; i < nr; i++) {
struct page *page = pages[i];
if (unlikely(PageCompound(page))) {
if (zone) {
spin_unlock_irqrestore(&zone->lru_lock, flags);
zone = NULL;
}
put_compound_page(page);
continue;
}
if (!put_page_testzero(page))
continue;
if (PageLRU(page)) {
struct zone *pagezone = page_zone(page);
if (pagezone != zone) {
if (zone)
spin_unlock_irqrestore(&zone->lru_lock,
flags);
zone = pagezone;
spin_lock_irqsave(&zone->lru_lock, flags);
}
lruvec = mem_cgroup_page_lruvec(page, zone);
VM_BUG_ON(!PageLRU(page));
__ClearPageLRU(page);
del_page_from_lru_list(page, lruvec, page_off_lru(page));
}
list_add(&page->lru, &pages_to_free);
}
if (zone)
spin_unlock_irqrestore(&zone->lru_lock, flags);
free_hot_cold_page_list(&pages_to_free, cold);
}
EXPORT_SYMBOL(release_pages);
/*
* The pages which we're about to release may be in the deferred lru-addition
* queues. That would prevent them from really being freed right now. That's
* OK from a correctness point of view but is inefficient - those pages may be
* cache-warm and we want to give them back to the page allocator ASAP.
*
* So __pagevec_release() will drain those queues here. __pagevec_lru_add()
* and __pagevec_lru_add_active() call release_pages() directly to avoid
* mutual recursion.
*/
void __pagevec_release(struct pagevec *pvec)
{
lru_add_drain();
release_pages(pvec->pages, pagevec_count(pvec), pvec->cold);
pagevec_reinit(pvec);
}
EXPORT_SYMBOL(__pagevec_release);
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
/* used by __split_huge_page_refcount() */
void lru_add_page_tail(struct page *page, struct page *page_tail,
struct lruvec *lruvec)
{
int uninitialized_var(active);
enum lru_list lru;
const int file = 0;
VM_BUG_ON(!PageHead(page));
VM_BUG_ON(PageCompound(page_tail));
VM_BUG_ON(PageLRU(page_tail));
VM_BUG_ON(NR_CPUS != 1 &&
!spin_is_locked(&lruvec_zone(lruvec)->lru_lock));
SetPageLRU(page_tail);
if (page_evictable(page_tail, NULL)) {
if (PageActive(page)) {
SetPageActive(page_tail);
active = 1;
lru = LRU_ACTIVE_ANON;
} else {
active = 0;
lru = LRU_INACTIVE_ANON;
}
} else {
SetPageUnevictable(page_tail);
lru = LRU_UNEVICTABLE;
}
if (likely(PageLRU(page)))
list_add_tail(&page_tail->lru, &page->lru);
else {
struct list_head *list_head;
/*
* Head page has not yet been counted, as an hpage,
* so we must account for each subpage individually.
*
* Use the standard add function to put page_tail on the list,
* but then correct its position so they all end up in order.
*/
add_page_to_lru_list(page_tail, lruvec, lru);
list_head = page_tail->lru.prev;
list_move_tail(&page_tail->lru, list_head);
}
if (!PageUnevictable(page))
update_page_reclaim_stat(lruvec, file, active);
}
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec,
void *arg)
{
enum lru_list lru = (enum lru_list)arg;
int file = is_file_lru(lru);
int active = is_active_lru(lru);
VM_BUG_ON(PageActive(page));
VM_BUG_ON(PageUnevictable(page));
VM_BUG_ON(PageLRU(page));
SetPageLRU(page);
if (active)
SetPageActive(page);
add_page_to_lru_list(page, lruvec, lru);
update_page_reclaim_stat(lruvec, file, active);
}
/*
* Add the passed pages to the LRU, then drop the caller's refcount
* on them. Reinitialises the caller's pagevec.
*/
void __pagevec_lru_add(struct pagevec *pvec, enum lru_list lru)
{
VM_BUG_ON(is_unevictable_lru(lru));
pagevec_lru_move_fn(pvec, __pagevec_lru_add_fn, (void *)lru);
}
EXPORT_SYMBOL(__pagevec_lru_add);
/**
* pagevec_lookup - gang pagecache lookup
* @pvec: Where the resulting pages are placed
* @mapping: The address_space to search
* @start: The starting page index
* @nr_pages: The maximum number of pages
*
* pagevec_lookup() will search for and return a group of up to @nr_pages pages
* in the mapping. The pages are placed in @pvec. pagevec_lookup() takes a
* reference against the pages in @pvec.
*
* The search returns a group of mapping-contiguous pages with ascending
* indexes. There may be holes in the indices due to not-present pages.
*
* pagevec_lookup() returns the number of pages which were found.
*/
unsigned pagevec_lookup(struct pagevec *pvec, struct address_space *mapping,
pgoff_t start, unsigned nr_pages)
{
pvec->nr = find_get_pages(mapping, start, nr_pages, pvec->pages);
return pagevec_count(pvec);
}
EXPORT_SYMBOL(pagevec_lookup);
unsigned pagevec_lookup_tag(struct pagevec *pvec, struct address_space *mapping,
pgoff_t *index, int tag, unsigned nr_pages)
{
pvec->nr = find_get_pages_tag(mapping, index, tag,
nr_pages, pvec->pages);
return pagevec_count(pvec);
}
EXPORT_SYMBOL(pagevec_lookup_tag);
/*
* Perform any setup for the swap system
*/
void __init swap_setup(void)
{
unsigned long megs = totalram_pages >> (20 - PAGE_SHIFT);
#ifdef CONFIG_SWAP
bdi_init(swapper_space.backing_dev_info);
#endif
/* Use a smaller cluster for small-memory machines */
if (megs < 16)
page_cluster = 2;
else
page_cluster = 3;
/*
* Right now other parts of the system means that we
* _really_ don't want to cluster much more
*/
}
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