android_kernel_motorola_sm6225/mm/migrate.c
Christoph Lameter 4c28f81193 [PATCH] page migration: Fix fallback behavior for dirty pages
Currently we check PageDirty() in order to make the decision to swap out
the page.  However, the dirty information may be only be contained in the
ptes pointing to the page.  We need to first unmap the ptes before checking
for PageDirty().  If unmap is successful then the page count of the page
will also be decreased so that pageout() works properly.

This is a fix necessary for 2.6.17.  Without this fix we may migrate dirty
pages for filesystems without migration functions.  Filesystems may keep
pointers to dirty pages.  Migration of dirty pages can result in the
filesystem keeping pointers to freed pages.

Unmapping is currently not be separated out from removing all the
references to a page and moving the mapping.  Therefore try_to_unmap will
be called again in migrate_page() if the writeout is successful.  However,
it wont do anything since the ptes are already removed.

The coming updates to the page migration code will restructure the code
so that this is no longer necessary.

Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-05-01 18:17:45 -07:00

662 lines
15 KiB
C

/*
* Memory Migration functionality - linux/mm/migration.c
*
* Copyright (C) 2006 Silicon Graphics, Inc., Christoph Lameter
*
* Page migration was first developed in the context of the memory hotplug
* project. The main authors of the migration code are:
*
* IWAMOTO Toshihiro <iwamoto@valinux.co.jp>
* Hirokazu Takahashi <taka@valinux.co.jp>
* Dave Hansen <haveblue@us.ibm.com>
* Christoph Lameter <clameter@sgi.com>
*/
#include <linux/migrate.h>
#include <linux/module.h>
#include <linux/swap.h>
#include <linux/pagemap.h>
#include <linux/buffer_head.h>
#include <linux/mm_inline.h>
#include <linux/pagevec.h>
#include <linux/rmap.h>
#include <linux/topology.h>
#include <linux/cpu.h>
#include <linux/cpuset.h>
#include <linux/swapops.h>
#include "internal.h"
/* The maximum number of pages to take off the LRU for migration */
#define MIGRATE_CHUNK_SIZE 256
#define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
/*
* Isolate one page from the LRU lists. If successful put it onto
* the indicated list with elevated page count.
*
* Result:
* -EBUSY: page not on LRU list
* 0: page removed from LRU list and added to the specified list.
*/
int isolate_lru_page(struct page *page, struct list_head *pagelist)
{
int ret = -EBUSY;
if (PageLRU(page)) {
struct zone *zone = page_zone(page);
spin_lock_irq(&zone->lru_lock);
if (PageLRU(page)) {
ret = 0;
get_page(page);
ClearPageLRU(page);
if (PageActive(page))
del_page_from_active_list(zone, page);
else
del_page_from_inactive_list(zone, page);
list_add_tail(&page->lru, pagelist);
}
spin_unlock_irq(&zone->lru_lock);
}
return ret;
}
/*
* migrate_prep() needs to be called after we have compiled the list of pages
* to be migrated using isolate_lru_page() but before we begin a series of calls
* to migrate_pages().
*/
int migrate_prep(void)
{
/* Must have swap device for migration */
if (nr_swap_pages <= 0)
return -ENODEV;
/*
* Clear the LRU lists so pages can be isolated.
* Note that pages may be moved off the LRU after we have
* drained them. Those pages will fail to migrate like other
* pages that may be busy.
*/
lru_add_drain_all();
return 0;
}
static inline void move_to_lru(struct page *page)
{
list_del(&page->lru);
if (PageActive(page)) {
/*
* lru_cache_add_active checks that
* the PG_active bit is off.
*/
ClearPageActive(page);
lru_cache_add_active(page);
} else {
lru_cache_add(page);
}
put_page(page);
}
/*
* Add isolated pages on the list back to the LRU.
*
* returns the number of pages put back.
*/
int putback_lru_pages(struct list_head *l)
{
struct page *page;
struct page *page2;
int count = 0;
list_for_each_entry_safe(page, page2, l, lru) {
move_to_lru(page);
count++;
}
return count;
}
/*
* Non migratable page
*/
int fail_migrate_page(struct page *newpage, struct page *page)
{
return -EIO;
}
EXPORT_SYMBOL(fail_migrate_page);
/*
* swapout a single page
* page is locked upon entry, unlocked on exit
*/
static int swap_page(struct page *page)
{
struct address_space *mapping = page_mapping(page);
if (page_mapped(page) && mapping)
if (try_to_unmap(page, 1) != SWAP_SUCCESS)
goto unlock_retry;
if (PageDirty(page)) {
/* Page is dirty, try to write it out here */
switch(pageout(page, mapping)) {
case PAGE_KEEP:
case PAGE_ACTIVATE:
goto unlock_retry;
case PAGE_SUCCESS:
goto retry;
case PAGE_CLEAN:
; /* try to free the page below */
}
}
if (PagePrivate(page)) {
if (!try_to_release_page(page, GFP_KERNEL) ||
(!mapping && page_count(page) == 1))
goto unlock_retry;
}
if (remove_mapping(mapping, page)) {
/* Success */
unlock_page(page);
return 0;
}
unlock_retry:
unlock_page(page);
retry:
return -EAGAIN;
}
/*
* Remove references for a page and establish the new page with the correct
* basic settings to be able to stop accesses to the page.
*/
int migrate_page_remove_references(struct page *newpage,
struct page *page, int nr_refs)
{
struct address_space *mapping = page_mapping(page);
struct page **radix_pointer;
/*
* Avoid doing any of the following work if the page count
* indicates that the page is in use or truncate has removed
* the page.
*/
if (!mapping || page_mapcount(page) + nr_refs != page_count(page))
return -EAGAIN;
/*
* Establish swap ptes for anonymous pages or destroy pte
* maps for files.
*
* In order to reestablish file backed mappings the fault handlers
* will take the radix tree_lock which may then be used to stop
* processses from accessing this page until the new page is ready.
*
* A process accessing via a swap pte (an anonymous page) will take a
* page_lock on the old page which will block the process until the
* migration attempt is complete. At that time the PageSwapCache bit
* will be examined. If the page was migrated then the PageSwapCache
* bit will be clear and the operation to retrieve the page will be
* retried which will find the new page in the radix tree. Then a new
* direct mapping may be generated based on the radix tree contents.
*
* If the page was not migrated then the PageSwapCache bit
* is still set and the operation may continue.
*/
if (try_to_unmap(page, 1) == SWAP_FAIL)
/* A vma has VM_LOCKED set -> permanent failure */
return -EPERM;
/*
* Give up if we were unable to remove all mappings.
*/
if (page_mapcount(page))
return -EAGAIN;
write_lock_irq(&mapping->tree_lock);
radix_pointer = (struct page **)radix_tree_lookup_slot(
&mapping->page_tree,
page_index(page));
if (!page_mapping(page) || page_count(page) != nr_refs ||
*radix_pointer != page) {
write_unlock_irq(&mapping->tree_lock);
return -EAGAIN;
}
/*
* Now we know that no one else is looking at the page.
*
* Certain minimal information about a page must be available
* in order for other subsystems to properly handle the page if they
* find it through the radix tree update before we are finished
* copying the page.
*/
get_page(newpage);
newpage->index = page->index;
newpage->mapping = page->mapping;
if (PageSwapCache(page)) {
SetPageSwapCache(newpage);
set_page_private(newpage, page_private(page));
}
*radix_pointer = newpage;
__put_page(page);
write_unlock_irq(&mapping->tree_lock);
return 0;
}
EXPORT_SYMBOL(migrate_page_remove_references);
/*
* Copy the page to its new location
*/
void migrate_page_copy(struct page *newpage, struct page *page)
{
copy_highpage(newpage, page);
if (PageError(page))
SetPageError(newpage);
if (PageReferenced(page))
SetPageReferenced(newpage);
if (PageUptodate(page))
SetPageUptodate(newpage);
if (PageActive(page))
SetPageActive(newpage);
if (PageChecked(page))
SetPageChecked(newpage);
if (PageMappedToDisk(page))
SetPageMappedToDisk(newpage);
if (PageDirty(page)) {
clear_page_dirty_for_io(page);
set_page_dirty(newpage);
}
ClearPageSwapCache(page);
ClearPageActive(page);
ClearPagePrivate(page);
set_page_private(page, 0);
page->mapping = NULL;
/*
* If any waiters have accumulated on the new page then
* wake them up.
*/
if (PageWriteback(newpage))
end_page_writeback(newpage);
}
EXPORT_SYMBOL(migrate_page_copy);
/*
* Common logic to directly migrate a single page suitable for
* pages that do not use PagePrivate.
*
* Pages are locked upon entry and exit.
*/
int migrate_page(struct page *newpage, struct page *page)
{
int rc;
BUG_ON(PageWriteback(page)); /* Writeback must be complete */
rc = migrate_page_remove_references(newpage, page, 2);
if (rc)
return rc;
migrate_page_copy(newpage, page);
/*
* Remove auxiliary swap entries and replace
* them with real ptes.
*
* Note that a real pte entry will allow processes that are not
* waiting on the page lock to use the new page via the page tables
* before the new page is unlocked.
*/
remove_from_swap(newpage);
return 0;
}
EXPORT_SYMBOL(migrate_page);
/*
* migrate_pages
*
* Two lists are passed to this function. The first list
* contains the pages isolated from the LRU to be migrated.
* The second list contains new pages that the pages isolated
* can be moved to. If the second list is NULL then all
* pages are swapped out.
*
* The function returns after 10 attempts or if no pages
* are movable anymore because to has become empty
* or no retryable pages exist anymore.
*
* Return: Number of pages not migrated when "to" ran empty.
*/
int migrate_pages(struct list_head *from, struct list_head *to,
struct list_head *moved, struct list_head *failed)
{
int retry;
int nr_failed = 0;
int pass = 0;
struct page *page;
struct page *page2;
int swapwrite = current->flags & PF_SWAPWRITE;
int rc;
if (!swapwrite)
current->flags |= PF_SWAPWRITE;
redo:
retry = 0;
list_for_each_entry_safe(page, page2, from, lru) {
struct page *newpage = NULL;
struct address_space *mapping;
cond_resched();
rc = 0;
if (page_count(page) == 1)
/* page was freed from under us. So we are done. */
goto next;
if (to && list_empty(to))
break;
/*
* Skip locked pages during the first two passes to give the
* functions holding the lock time to release the page. Later we
* use lock_page() to have a higher chance of acquiring the
* lock.
*/
rc = -EAGAIN;
if (pass > 2)
lock_page(page);
else
if (TestSetPageLocked(page))
goto next;
/*
* Only wait on writeback if we have already done a pass where
* we we may have triggered writeouts for lots of pages.
*/
if (pass > 0) {
wait_on_page_writeback(page);
} else {
if (PageWriteback(page))
goto unlock_page;
}
/*
* Anonymous pages must have swap cache references otherwise
* the information contained in the page maps cannot be
* preserved.
*/
if (PageAnon(page) && !PageSwapCache(page)) {
if (!add_to_swap(page, GFP_KERNEL)) {
rc = -ENOMEM;
goto unlock_page;
}
}
if (!to) {
rc = swap_page(page);
goto next;
}
newpage = lru_to_page(to);
lock_page(newpage);
/*
* Pages are properly locked and writeback is complete.
* Try to migrate the page.
*/
mapping = page_mapping(page);
if (!mapping)
goto unlock_both;
if (mapping->a_ops->migratepage) {
/*
* Most pages have a mapping and most filesystems
* should provide a migration function. Anonymous
* pages are part of swap space which also has its
* own migration function. This is the most common
* path for page migration.
*/
rc = mapping->a_ops->migratepage(newpage, page);
goto unlock_both;
}
/* Make sure the dirty bit is up to date */
if (try_to_unmap(page, 1) == SWAP_FAIL) {
rc = -EPERM;
goto unlock_both;
}
if (page_mapcount(page)) {
rc = -EAGAIN;
goto unlock_both;
}
/*
* Default handling if a filesystem does not provide
* a migration function. We can only migrate clean
* pages so try to write out any dirty pages first.
*/
if (PageDirty(page)) {
switch (pageout(page, mapping)) {
case PAGE_KEEP:
case PAGE_ACTIVATE:
goto unlock_both;
case PAGE_SUCCESS:
unlock_page(newpage);
goto next;
case PAGE_CLEAN:
; /* try to migrate the page below */
}
}
/*
* Buffers are managed in a filesystem specific way.
* We must have no buffers or drop them.
*/
if (!page_has_buffers(page) ||
try_to_release_page(page, GFP_KERNEL)) {
rc = migrate_page(newpage, page);
goto unlock_both;
}
/*
* On early passes with mapped pages simply
* retry. There may be a lock held for some
* buffers that may go away. Later
* swap them out.
*/
if (pass > 4) {
/*
* Persistently unable to drop buffers..... As a
* measure of last resort we fall back to
* swap_page().
*/
unlock_page(newpage);
newpage = NULL;
rc = swap_page(page);
goto next;
}
unlock_both:
unlock_page(newpage);
unlock_page:
unlock_page(page);
next:
if (rc == -EAGAIN) {
retry++;
} else if (rc) {
/* Permanent failure */
list_move(&page->lru, failed);
nr_failed++;
} else {
if (newpage) {
/* Successful migration. Return page to LRU */
move_to_lru(newpage);
}
list_move(&page->lru, moved);
}
}
if (retry && pass++ < 10)
goto redo;
if (!swapwrite)
current->flags &= ~PF_SWAPWRITE;
return nr_failed + retry;
}
/*
* Migration function for pages with buffers. This function can only be used
* if the underlying filesystem guarantees that no other references to "page"
* exist.
*/
int buffer_migrate_page(struct page *newpage, struct page *page)
{
struct address_space *mapping = page->mapping;
struct buffer_head *bh, *head;
int rc;
if (!mapping)
return -EAGAIN;
if (!page_has_buffers(page))
return migrate_page(newpage, page);
head = page_buffers(page);
rc = migrate_page_remove_references(newpage, page, 3);
if (rc)
return rc;
bh = head;
do {
get_bh(bh);
lock_buffer(bh);
bh = bh->b_this_page;
} while (bh != head);
ClearPagePrivate(page);
set_page_private(newpage, page_private(page));
set_page_private(page, 0);
put_page(page);
get_page(newpage);
bh = head;
do {
set_bh_page(bh, newpage, bh_offset(bh));
bh = bh->b_this_page;
} while (bh != head);
SetPagePrivate(newpage);
migrate_page_copy(newpage, page);
bh = head;
do {
unlock_buffer(bh);
put_bh(bh);
bh = bh->b_this_page;
} while (bh != head);
return 0;
}
EXPORT_SYMBOL(buffer_migrate_page);
/*
* Migrate the list 'pagelist' of pages to a certain destination.
*
* Specify destination with either non-NULL vma or dest_node >= 0
* Return the number of pages not migrated or error code
*/
int migrate_pages_to(struct list_head *pagelist,
struct vm_area_struct *vma, int dest)
{
LIST_HEAD(newlist);
LIST_HEAD(moved);
LIST_HEAD(failed);
int err = 0;
unsigned long offset = 0;
int nr_pages;
struct page *page;
struct list_head *p;
redo:
nr_pages = 0;
list_for_each(p, pagelist) {
if (vma) {
/*
* The address passed to alloc_page_vma is used to
* generate the proper interleave behavior. We fake
* the address here by an increasing offset in order
* to get the proper distribution of pages.
*
* No decision has been made as to which page
* a certain old page is moved to so we cannot
* specify the correct address.
*/
page = alloc_page_vma(GFP_HIGHUSER, vma,
offset + vma->vm_start);
offset += PAGE_SIZE;
}
else
page = alloc_pages_node(dest, GFP_HIGHUSER, 0);
if (!page) {
err = -ENOMEM;
goto out;
}
list_add_tail(&page->lru, &newlist);
nr_pages++;
if (nr_pages > MIGRATE_CHUNK_SIZE)
break;
}
err = migrate_pages(pagelist, &newlist, &moved, &failed);
putback_lru_pages(&moved); /* Call release pages instead ?? */
if (err >= 0 && list_empty(&newlist) && !list_empty(pagelist))
goto redo;
out:
/* Return leftover allocated pages */
while (!list_empty(&newlist)) {
page = list_entry(newlist.next, struct page, lru);
list_del(&page->lru);
__free_page(page);
}
list_splice(&failed, pagelist);
if (err < 0)
return err;
/* Calculate number of leftover pages */
nr_pages = 0;
list_for_each(p, pagelist)
nr_pages++;
return nr_pages;
}