blob: 5c5cb2d67b31fcb5fbfb85aca09878282731ac0f [file] [log] [blame]
// SPDX-License-Identifier: GPL-2.0
/*
* linux/mm/swap_state.c
*
* Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
* Swap reorganised 29.12.95, Stephen Tweedie
*
* Rewritten to use page cache, (C) 1998 Stephen Tweedie
*/
#include <linux/mm.h>
#include <linux/gfp.h>
#include <linux/kernel_stat.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/init.h>
#include <linux/pagemap.h>
#include <linux/backing-dev.h>
#include <linux/blkdev.h>
#include <linux/pagevec.h>
#include <linux/migrate.h>
#include <linux/vmalloc.h>
#include <linux/swap_slots.h>
#include <linux/huge_mm.h>
#include <linux/shmem_fs.h>
#include "internal.h"
/*
* swapper_space is a fiction, retained to simplify the path through
* vmscan's shrink_page_list.
*/
static const struct address_space_operations swap_aops = {
.writepage = swap_writepage,
.set_page_dirty = swap_set_page_dirty,
#ifdef CONFIG_MIGRATION
.migratepage = migrate_page,
#endif
};
struct address_space *swapper_spaces[MAX_SWAPFILES] __read_mostly;
static unsigned int nr_swapper_spaces[MAX_SWAPFILES] __read_mostly;
static bool enable_vma_readahead __read_mostly = true;
#define SWAP_RA_WIN_SHIFT (PAGE_SHIFT / 2)
#define SWAP_RA_HITS_MASK ((1UL << SWAP_RA_WIN_SHIFT) - 1)
#define SWAP_RA_HITS_MAX SWAP_RA_HITS_MASK
#define SWAP_RA_WIN_MASK (~PAGE_MASK & ~SWAP_RA_HITS_MASK)
#define SWAP_RA_HITS(v) ((v) & SWAP_RA_HITS_MASK)
#define SWAP_RA_WIN(v) (((v) & SWAP_RA_WIN_MASK) >> SWAP_RA_WIN_SHIFT)
#define SWAP_RA_ADDR(v) ((v) & PAGE_MASK)
#define SWAP_RA_VAL(addr, win, hits) \
(((addr) & PAGE_MASK) | \
(((win) << SWAP_RA_WIN_SHIFT) & SWAP_RA_WIN_MASK) | \
((hits) & SWAP_RA_HITS_MASK))
/* Initial readahead hits is 4 to start up with a small window */
#define GET_SWAP_RA_VAL(vma) \
(atomic_long_read(&(vma)->swap_readahead_info) ? : 4)
#define INC_CACHE_INFO(x) data_race(swap_cache_info.x++)
#define ADD_CACHE_INFO(x, nr) data_race(swap_cache_info.x += (nr))
static struct {
unsigned long add_total;
unsigned long del_total;
unsigned long find_success;
unsigned long find_total;
} swap_cache_info;
unsigned long total_swapcache_pages(void)
{
unsigned int i, j, nr;
unsigned long ret = 0;
struct address_space *spaces;
struct swap_info_struct *si;
for (i = 0; i < MAX_SWAPFILES; i++) {
swp_entry_t entry = swp_entry(i, 1);
/* Avoid get_swap_device() to warn for bad swap entry */
if (!swp_swap_info(entry))
continue;
/* Prevent swapoff to free swapper_spaces */
si = get_swap_device(entry);
if (!si)
continue;
nr = nr_swapper_spaces[i];
spaces = swapper_spaces[i];
for (j = 0; j < nr; j++)
ret += spaces[j].nrpages;
put_swap_device(si);
}
return ret;
}
static atomic_t swapin_readahead_hits = ATOMIC_INIT(4);
void show_swap_cache_info(void)
{
printk("%lu pages in swap cache\n", total_swapcache_pages());
printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
swap_cache_info.add_total, swap_cache_info.del_total,
swap_cache_info.find_success, swap_cache_info.find_total);
printk("Free swap = %ldkB\n",
get_nr_swap_pages() << (PAGE_SHIFT - 10));
printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
}
void *get_shadow_from_swap_cache(swp_entry_t entry)
{
struct address_space *address_space = swap_address_space(entry);
pgoff_t idx = swp_offset(entry);
struct page *page;
page = find_get_entry(address_space, idx);
if (xa_is_value(page))
return page;
if (page)
put_page(page);
return NULL;
}
/*
* add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
* but sets SwapCache flag and private instead of mapping and index.
*/
int add_to_swap_cache(struct page *page, swp_entry_t entry,
gfp_t gfp, void **shadowp)
{
struct address_space *address_space = swap_address_space(entry);
pgoff_t idx = swp_offset(entry);
XA_STATE_ORDER(xas, &address_space->i_pages, idx, compound_order(page));
unsigned long i, nr = thp_nr_pages(page);
void *old;
VM_BUG_ON_PAGE(!PageLocked(page), page);
VM_BUG_ON_PAGE(PageSwapCache(page), page);
VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
page_ref_add(page, nr);
SetPageSwapCache(page);
do {
unsigned long nr_shadows = 0;
xas_lock_irq(&xas);
xas_create_range(&xas);
if (xas_error(&xas))
goto unlock;
for (i = 0; i < nr; i++) {
VM_BUG_ON_PAGE(xas.xa_index != idx + i, page);
old = xas_load(&xas);
if (xa_is_value(old)) {
nr_shadows++;
if (shadowp)
*shadowp = old;
}
set_page_private(page + i, entry.val + i);
xas_store(&xas, page);
xas_next(&xas);
}
address_space->nrexceptional -= nr_shadows;
address_space->nrpages += nr;
__mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, nr);
ADD_CACHE_INFO(add_total, nr);
unlock:
xas_unlock_irq(&xas);
} while (xas_nomem(&xas, gfp));
if (!xas_error(&xas))
return 0;
ClearPageSwapCache(page);
page_ref_sub(page, nr);
return xas_error(&xas);
}
/*
* This must be called only on pages that have
* been verified to be in the swap cache.
*/
void __delete_from_swap_cache(struct page *page,
swp_entry_t entry, void *shadow)
{
struct address_space *address_space = swap_address_space(entry);
int i, nr = thp_nr_pages(page);
pgoff_t idx = swp_offset(entry);
XA_STATE(xas, &address_space->i_pages, idx);
VM_BUG_ON_PAGE(!PageLocked(page), page);
VM_BUG_ON_PAGE(!PageSwapCache(page), page);
VM_BUG_ON_PAGE(PageWriteback(page), page);
for (i = 0; i < nr; i++) {
void *entry = xas_store(&xas, shadow);
VM_BUG_ON_PAGE(entry != page, entry);
set_page_private(page + i, 0);
xas_next(&xas);
}
ClearPageSwapCache(page);
if (shadow)
address_space->nrexceptional += nr;
address_space->nrpages -= nr;
__mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, -nr);
ADD_CACHE_INFO(del_total, nr);
}
/**
* add_to_swap - allocate swap space for a page
* @page: page we want to move to swap
*
* Allocate swap space for the page and add the page to the
* swap cache. Caller needs to hold the page lock.
*/
int add_to_swap(struct page *page)
{
swp_entry_t entry;
int err;
VM_BUG_ON_PAGE(!PageLocked(page), page);
VM_BUG_ON_PAGE(!PageUptodate(page), page);
entry = get_swap_page(page);
if (!entry.val)
return 0;
/*
* XArray node allocations from PF_MEMALLOC contexts could
* completely exhaust the page allocator. __GFP_NOMEMALLOC
* stops emergency reserves from being allocated.
*
* TODO: this could cause a theoretical memory reclaim
* deadlock in the swap out path.
*/
/*
* Add it to the swap cache.
*/
err = add_to_swap_cache(page, entry,
__GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN, NULL);
if (err)
/*
* add_to_swap_cache() doesn't return -EEXIST, so we can safely
* clear SWAP_HAS_CACHE flag.
*/
goto fail;
/*
* Normally the page will be dirtied in unmap because its pte should be
* dirty. A special case is MADV_FREE page. The page's pte could have
* dirty bit cleared but the page's SwapBacked bit is still set because
* clearing the dirty bit and SwapBacked bit has no lock protected. For
* such page, unmap will not set dirty bit for it, so page reclaim will
* not write the page out. This can cause data corruption when the page
* is swap in later. Always setting the dirty bit for the page solves
* the problem.
*/
set_page_dirty(page);
return 1;
fail:
put_swap_page(page, entry);
return 0;
}
/*
* This must be called only on pages that have
* been verified to be in the swap cache and locked.
* It will never put the page into the free list,
* the caller has a reference on the page.
*/
void delete_from_swap_cache(struct page *page)
{
swp_entry_t entry = { .val = page_private(page) };
struct address_space *address_space = swap_address_space(entry);
xa_lock_irq(&address_space->i_pages);
__delete_from_swap_cache(page, entry, NULL);
xa_unlock_irq(&address_space->i_pages);
put_swap_page(page, entry);
page_ref_sub(page, thp_nr_pages(page));
}
void clear_shadow_from_swap_cache(int type, unsigned long begin,
unsigned long end)
{
unsigned long curr = begin;
void *old;
for (;;) {
unsigned long nr_shadows = 0;
swp_entry_t entry = swp_entry(type, curr);
struct address_space *address_space = swap_address_space(entry);
XA_STATE(xas, &address_space->i_pages, curr);
xa_lock_irq(&address_space->i_pages);
xas_for_each(&xas, old, end) {
if (!xa_is_value(old))
continue;
xas_store(&xas, NULL);
nr_shadows++;
}
address_space->nrexceptional -= nr_shadows;
xa_unlock_irq(&address_space->i_pages);
/* search the next swapcache until we meet end */
curr >>= SWAP_ADDRESS_SPACE_SHIFT;
curr++;
curr <<= SWAP_ADDRESS_SPACE_SHIFT;
if (curr > end)
break;
}
}
/*
* If we are the only user, then try to free up the swap cache.
*
* Its ok to check for PageSwapCache without the page lock
* here because we are going to recheck again inside
* try_to_free_swap() _with_ the lock.
* - Marcelo
*/
static inline void free_swap_cache(struct page *page)
{
if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
try_to_free_swap(page);
unlock_page(page);
}
}
/*
* Perform a free_page(), also freeing any swap cache associated with
* this page if it is the last user of the page.
*/
void free_page_and_swap_cache(struct page *page)
{
free_swap_cache(page);
if (!is_huge_zero_page(page))
put_page(page);
}
/*
* Passed an array of pages, drop them all from swapcache and then release
* them. They are removed from the LRU and freed if this is their last use.
*/
void free_pages_and_swap_cache(struct page **pages, int nr)
{
struct page **pagep = pages;
int i;
lru_add_drain();
for (i = 0; i < nr; i++)
free_swap_cache(pagep[i]);
release_pages(pagep, nr);
}
static inline bool swap_use_vma_readahead(void)
{
return READ_ONCE(enable_vma_readahead) && !atomic_read(&nr_rotate_swap);
}
/*
* Lookup a swap entry in the swap cache. A found page will be returned
* unlocked and with its refcount incremented - we rely on the kernel
* lock getting page table operations atomic even if we drop the page
* lock before returning.
*/
struct page *lookup_swap_cache(swp_entry_t entry, struct vm_area_struct *vma,
unsigned long addr)
{
struct page *page;
struct swap_info_struct *si;
si = get_swap_device(entry);
if (!si)
return NULL;
page = find_get_page(swap_address_space(entry), swp_offset(entry));
put_swap_device(si);
INC_CACHE_INFO(find_total);
if (page) {
bool vma_ra = swap_use_vma_readahead();
bool readahead;
INC_CACHE_INFO(find_success);
/*
* At the moment, we don't support PG_readahead for anon THP
* so let's bail out rather than confusing the readahead stat.
*/
if (unlikely(PageTransCompound(page)))
return page;
readahead = TestClearPageReadahead(page);
if (vma && vma_ra) {
unsigned long ra_val;
int win, hits;
ra_val = GET_SWAP_RA_VAL(vma);
win = SWAP_RA_WIN(ra_val);
hits = SWAP_RA_HITS(ra_val);
if (readahead)
hits = min_t(int, hits + 1, SWAP_RA_HITS_MAX);
atomic_long_set(&vma->swap_readahead_info,
SWAP_RA_VAL(addr, win, hits));
}
if (readahead) {
count_vm_event(SWAP_RA_HIT);
if (!vma || !vma_ra)
atomic_inc(&swapin_readahead_hits);
}
}
return page;
}
/**
* find_get_incore_page - Find and get a page from the page or swap caches.
* @mapping: The address_space to search.
* @index: The page cache index.
*
* This differs from find_get_page() in that it will also look for the
* page in the swap cache.
*
* Return: The found page or %NULL.
*/
struct page *find_get_incore_page(struct address_space *mapping, pgoff_t index)
{
swp_entry_t swp;
struct swap_info_struct *si;
struct page *page = find_get_entry(mapping, index);
if (!page)
return page;
if (!xa_is_value(page))
return find_subpage(page, index);
if (!shmem_mapping(mapping))
return NULL;
swp = radix_to_swp_entry(page);
/* Prevent swapoff from happening to us */
si = get_swap_device(swp);
if (!si)
return NULL;
page = find_get_page(swap_address_space(swp), swp_offset(swp));
put_swap_device(si);
return page;
}
struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
struct vm_area_struct *vma, unsigned long addr,
bool *new_page_allocated)
{
struct swap_info_struct *si;
struct page *page;
void *shadow = NULL;
*new_page_allocated = false;
for (;;) {
int err;
/*
* First check the swap cache. Since this is normally
* called after lookup_swap_cache() failed, re-calling
* that would confuse statistics.
*/
si = get_swap_device(entry);
if (!si)
return NULL;
page = find_get_page(swap_address_space(entry),
swp_offset(entry));
put_swap_device(si);
if (page)
return page;
/*
* Just skip read ahead for unused swap slot.
* During swap_off when swap_slot_cache is disabled,
* we have to handle the race between putting
* swap entry in swap cache and marking swap slot
* as SWAP_HAS_CACHE. That's done in later part of code or
* else swap_off will be aborted if we return NULL.
*/
if (!__swp_swapcount(entry) && swap_slot_cache_enabled)
return NULL;
/*
* Get a new page to read into from swap. Allocate it now,
* before marking swap_map SWAP_HAS_CACHE, when -EEXIST will
* cause any racers to loop around until we add it to cache.
*/
page = alloc_page_vma(gfp_mask, vma, addr);
if (!page)
return NULL;
/*
* Swap entry may have been freed since our caller observed it.
*/
err = swapcache_prepare(entry);
if (!err)
break;
put_page(page);
if (err != -EEXIST)
return NULL;
/*
* We might race against __delete_from_swap_cache(), and
* stumble across a swap_map entry whose SWAP_HAS_CACHE
* has not yet been cleared. Or race against another
* __read_swap_cache_async(), which has set SWAP_HAS_CACHE
* in swap_map, but not yet added its page to swap cache.
*/
schedule_timeout_uninterruptible(1);
}
/*
* The swap entry is ours to swap in. Prepare the new page.
*/
__SetPageLocked(page);
__SetPageSwapBacked(page);
/* May fail (-ENOMEM) if XArray node allocation failed. */
if (add_to_swap_cache(page, entry, gfp_mask & GFP_RECLAIM_MASK, &shadow)) {
put_swap_page(page, entry);
goto fail_unlock;
}
if (mem_cgroup_charge(page, NULL, gfp_mask)) {
delete_from_swap_cache(page);
goto fail_unlock;
}
if (shadow)
workingset_refault(page, shadow);
/* Caller will initiate read into locked page */
SetPageWorkingset(page);
lru_cache_add(page);
*new_page_allocated = true;
return page;
fail_unlock:
unlock_page(page);
put_page(page);
return NULL;
}
/*
* Locate a page of swap in physical memory, reserving swap cache space
* and reading the disk if it is not already cached.
* A failure return means that either the page allocation failed or that
* the swap entry is no longer in use.
*/
struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
struct vm_area_struct *vma, unsigned long addr, bool do_poll)
{
bool page_was_allocated;
struct page *retpage = __read_swap_cache_async(entry, gfp_mask,
vma, addr, &page_was_allocated);
if (page_was_allocated)
swap_readpage(retpage, do_poll);
return retpage;
}
static unsigned int __swapin_nr_pages(unsigned long prev_offset,
unsigned long offset,
int hits,
int max_pages,
int prev_win)
{
unsigned int pages, last_ra;
/*
* This heuristic has been found to work well on both sequential and
* random loads, swapping to hard disk or to SSD: please don't ask
* what the "+ 2" means, it just happens to work well, that's all.
*/
pages = hits + 2;
if (pages == 2) {
/*
* We can have no readahead hits to judge by: but must not get
* stuck here forever, so check for an adjacent offset instead
* (and don't even bother to check whether swap type is same).
*/
if (offset != prev_offset + 1 && offset != prev_offset - 1)
pages = 1;
} else {
unsigned int roundup = 4;
while (roundup < pages)
roundup <<= 1;
pages = roundup;
}
if (pages > max_pages)
pages = max_pages;
/* Don't shrink readahead too fast */
last_ra = prev_win / 2;
if (pages < last_ra)
pages = last_ra;
return pages;
}
static unsigned long swapin_nr_pages(unsigned long offset)
{
static unsigned long prev_offset;
unsigned int hits, pages, max_pages;
static atomic_t last_readahead_pages;
max_pages = 1 << READ_ONCE(page_cluster);
if (max_pages <= 1)
return 1;
hits = atomic_xchg(&swapin_readahead_hits, 0);
pages = __swapin_nr_pages(READ_ONCE(prev_offset), offset, hits,
max_pages,
atomic_read(&last_readahead_pages));
if (!hits)
WRITE_ONCE(prev_offset, offset);
atomic_set(&last_readahead_pages, pages);
return pages;
}
/**
* swap_cluster_readahead - swap in pages in hope we need them soon
* @entry: swap entry of this memory
* @gfp_mask: memory allocation flags
* @vmf: fault information
*
* Returns the struct page for entry and addr, after queueing swapin.
*
* Primitive swap readahead code. We simply read an aligned block of
* (1 << page_cluster) entries in the swap area. This method is chosen
* because it doesn't cost us any seek time. We also make sure to queue
* the 'original' request together with the readahead ones...
*
* This has been extended to use the NUMA policies from the mm triggering
* the readahead.
*
* Caller must hold read mmap_lock if vmf->vma is not NULL.
*/
struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
struct vm_fault *vmf)
{
struct page *page;
unsigned long entry_offset = swp_offset(entry);
unsigned long offset = entry_offset;
unsigned long start_offset, end_offset;
unsigned long mask;
struct swap_info_struct *si = swp_swap_info(entry);
struct blk_plug plug;
bool do_poll = true, page_allocated;
struct vm_area_struct *vma = vmf->vma;
unsigned long addr = vmf->address;
mask = swapin_nr_pages(offset) - 1;
if (!mask)
goto skip;
/* Test swap type to make sure the dereference is safe */
if (likely(si->flags & (SWP_BLKDEV | SWP_FS_OPS))) {
struct inode *inode = si->swap_file->f_mapping->host;
if (inode_read_congested(inode))
goto skip;
}
do_poll = false;
/* Read a page_cluster sized and aligned cluster around offset. */
start_offset = offset & ~mask;
end_offset = offset | mask;
if (!start_offset) /* First page is swap header. */
start_offset++;
if (end_offset >= si->max)
end_offset = si->max - 1;
blk_start_plug(&plug);
for (offset = start_offset; offset <= end_offset ; offset++) {
/* Ok, do the async read-ahead now */
page = __read_swap_cache_async(
swp_entry(swp_type(entry), offset),
gfp_mask, vma, addr, &page_allocated);
if (!page)
continue;
if (page_allocated) {
swap_readpage(page, false);
if (offset != entry_offset) {
SetPageReadahead(page);
count_vm_event(SWAP_RA);
}
}
put_page(page);
}
blk_finish_plug(&plug);
lru_add_drain(); /* Push any new pages onto the LRU now */
skip:
return read_swap_cache_async(entry, gfp_mask, vma, addr, do_poll);
}
int init_swap_address_space(unsigned int type, unsigned long nr_pages)
{
struct address_space *spaces, *space;
unsigned int i, nr;
nr = DIV_ROUND_UP(nr_pages, SWAP_ADDRESS_SPACE_PAGES);
spaces = kvcalloc(nr, sizeof(struct address_space), GFP_KERNEL);
if (!spaces)
return -ENOMEM;
for (i = 0; i < nr; i++) {
space = spaces + i;
xa_init_flags(&space->i_pages, XA_FLAGS_LOCK_IRQ);
atomic_set(&space->i_mmap_writable, 0);
space->a_ops = &swap_aops;
/* swap cache doesn't use writeback related tags */
mapping_set_no_writeback_tags(space);
}
nr_swapper_spaces[type] = nr;
swapper_spaces[type] = spaces;
return 0;
}
void exit_swap_address_space(unsigned int type)
{
kvfree(swapper_spaces[type]);
nr_swapper_spaces[type] = 0;
swapper_spaces[type] = NULL;
}
static inline void swap_ra_clamp_pfn(struct vm_area_struct *vma,
unsigned long faddr,
unsigned long lpfn,
unsigned long rpfn,
unsigned long *start,
unsigned long *end)
{
*start = max3(lpfn, PFN_DOWN(vma->vm_start),
PFN_DOWN(faddr & PMD_MASK));
*end = min3(rpfn, PFN_DOWN(vma->vm_end),
PFN_DOWN((faddr & PMD_MASK) + PMD_SIZE));
}
static void swap_ra_info(struct vm_fault *vmf,
struct vma_swap_readahead *ra_info)
{
struct vm_area_struct *vma = vmf->vma;
unsigned long ra_val;
swp_entry_t entry;
unsigned long faddr, pfn, fpfn;
unsigned long start, end;
pte_t *pte, *orig_pte;
unsigned int max_win, hits, prev_win, win, left;
#ifndef CONFIG_64BIT
pte_t *tpte;
#endif
max_win = 1 << min_t(unsigned int, READ_ONCE(page_cluster),
SWAP_RA_ORDER_CEILING);
if (max_win == 1) {
ra_info->win = 1;
return;
}
faddr = vmf->address;
orig_pte = pte = pte_offset_map(vmf->pmd, faddr);
entry = pte_to_swp_entry(*pte);
if ((unlikely(non_swap_entry(entry)))) {
pte_unmap(orig_pte);
return;
}
fpfn = PFN_DOWN(faddr);
ra_val = GET_SWAP_RA_VAL(vma);
pfn = PFN_DOWN(SWAP_RA_ADDR(ra_val));
prev_win = SWAP_RA_WIN(ra_val);
hits = SWAP_RA_HITS(ra_val);
ra_info->win = win = __swapin_nr_pages(pfn, fpfn, hits,
max_win, prev_win);
atomic_long_set(&vma->swap_readahead_info,
SWAP_RA_VAL(faddr, win, 0));
if (win == 1) {
pte_unmap(orig_pte);
return;
}
/* Copy the PTEs because the page table may be unmapped */
if (fpfn == pfn + 1)
swap_ra_clamp_pfn(vma, faddr, fpfn, fpfn + win, &start, &end);
else if (pfn == fpfn + 1)
swap_ra_clamp_pfn(vma, faddr, fpfn - win + 1, fpfn + 1,
&start, &end);
else {
left = (win - 1) / 2;
swap_ra_clamp_pfn(vma, faddr, fpfn - left, fpfn + win - left,
&start, &end);
}
ra_info->nr_pte = end - start;
ra_info->offset = fpfn - start;
pte -= ra_info->offset;
#ifdef CONFIG_64BIT
ra_info->ptes = pte;
#else
tpte = ra_info->ptes;
for (pfn = start; pfn != end; pfn++)
*tpte++ = *pte++;
#endif
pte_unmap(orig_pte);
}
/**
* swap_vma_readahead - swap in pages in hope we need them soon
* @fentry: swap entry of this memory
* @gfp_mask: memory allocation flags
* @vmf: fault information
*
* Returns the struct page for entry and addr, after queueing swapin.
*
* Primitive swap readahead code. We simply read in a few pages whoes
* virtual addresses are around the fault address in the same vma.
*
* Caller must hold read mmap_lock if vmf->vma is not NULL.
*
*/
static struct page *swap_vma_readahead(swp_entry_t fentry, gfp_t gfp_mask,
struct vm_fault *vmf)
{
struct blk_plug plug;
struct vm_area_struct *vma = vmf->vma;
struct page *page;
pte_t *pte, pentry;
swp_entry_t entry;
unsigned int i;
bool page_allocated;
struct vma_swap_readahead ra_info = {0,};
swap_ra_info(vmf, &ra_info);
if (ra_info.win == 1)
goto skip;
blk_start_plug(&plug);
for (i = 0, pte = ra_info.ptes; i < ra_info.nr_pte;
i++, pte++) {
pentry = *pte;
if (pte_none(pentry))
continue;
if (pte_present(pentry))
continue;
entry = pte_to_swp_entry(pentry);
if (unlikely(non_swap_entry(entry)))
continue;
page = __read_swap_cache_async(entry, gfp_mask, vma,
vmf->address, &page_allocated);
if (!page)
continue;
if (page_allocated) {
swap_readpage(page, false);
if (i != ra_info.offset) {
SetPageReadahead(page);
count_vm_event(SWAP_RA);
}
}
put_page(page);
}
blk_finish_plug(&plug);
lru_add_drain();
skip:
return read_swap_cache_async(fentry, gfp_mask, vma, vmf->address,
ra_info.win == 1);
}
/**
* swapin_readahead - swap in pages in hope we need them soon
* @entry: swap entry of this memory
* @gfp_mask: memory allocation flags
* @vmf: fault information
*
* Returns the struct page for entry and addr, after queueing swapin.
*
* It's a main entry function for swap readahead. By the configuration,
* it will read ahead blocks by cluster-based(ie, physical disk based)
* or vma-based(ie, virtual address based on faulty address) readahead.
*/
struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
struct vm_fault *vmf)
{
return swap_use_vma_readahead() ?
swap_vma_readahead(entry, gfp_mask, vmf) :
swap_cluster_readahead(entry, gfp_mask, vmf);
}
#ifdef CONFIG_SYSFS
static ssize_t vma_ra_enabled_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
return sprintf(buf, "%s\n", enable_vma_readahead ? "true" : "false");
}
static ssize_t vma_ra_enabled_store(struct kobject *kobj,
struct kobj_attribute *attr,
const char *buf, size_t count)
{
if (!strncmp(buf, "true", 4) || !strncmp(buf, "1", 1))
enable_vma_readahead = true;
else if (!strncmp(buf, "false", 5) || !strncmp(buf, "0", 1))
enable_vma_readahead = false;
else
return -EINVAL;
return count;
}
static struct kobj_attribute vma_ra_enabled_attr =
__ATTR(vma_ra_enabled, 0644, vma_ra_enabled_show,
vma_ra_enabled_store);
static struct attribute *swap_attrs[] = {
&vma_ra_enabled_attr.attr,
NULL,
};
static struct attribute_group swap_attr_group = {
.attrs = swap_attrs,
};
static int __init swap_init_sysfs(void)
{
int err;
struct kobject *swap_kobj;
swap_kobj = kobject_create_and_add("swap", mm_kobj);
if (!swap_kobj) {
pr_err("failed to create swap kobject\n");
return -ENOMEM;
}
err = sysfs_create_group(swap_kobj, &swap_attr_group);
if (err) {
pr_err("failed to register swap group\n");
goto delete_obj;
}
return 0;
delete_obj:
kobject_put(swap_kobj);
return err;
}
subsys_initcall(swap_init_sysfs);
#endif