5 files changed, 360 insertions, 22 deletions

diff --git a/Documentation/vm/page_migration b/Documentation/vm/page_migration
new file mode 100644
index 000000000000..c52820fcf500
--- /dev/null
+++ b/Documentation/vm/page_migration
@@ -0,0 +1,129 @@
+Page migration
+--------------
+
+Page migration allows the moving of the physical location of pages between
+nodes in a numa system while the process is running. This means that the
+virtual addresses that the process sees do not change. However, the
+system rearranges the physical location of those pages.
+
+The main intend of page migration is to reduce the latency of memory access
+by moving pages near to the processor where the process accessing that memory
+is running.
+
+Page migration allows a process to manually relocate the node on which its
+pages are located through the MF_MOVE and MF_MOVE_ALL options while setting
+a new memory policy. The pages of process can also be relocated
+from another process using the sys_migrate_pages() function call. The
+migrate_pages function call takes two sets of nodes and moves pages of a
+process that are located on the from nodes to the destination nodes.
+
+Manual migration is very useful if for example the scheduler has relocated
+a process to a processor on a distant node. A batch scheduler or an
+administrator may detect the situation and move the pages of the process
+nearer to the new processor. At some point in the future we may have
+some mechanism in the scheduler that will automatically move the pages.
+
+Larger installations usually partition the system using cpusets into
+sections of nodes. Paul Jackson has equipped cpusets with the ability to
+move pages when a task is moved to another cpuset. This allows automatic
+control over locality of a process. If a task is moved to a new cpuset
+then also all its pages are moved with it so that the performance of the
+process does not sink dramatically (as is the case today).
+
+Page migration allows the preservation of the relative location of pages
+within a group of nodes for all migration techniques which will preserve a
+particular memory allocation pattern generated even after migrating a
+process. This is necessary in order to preserve the memory latencies.
+Processes will run with similar performance after migration.
+
+Page migration occurs in several steps. First a high level
+description for those trying to use migrate_pages() and then
+a low level description of how the low level details work.
+
+A. Use of migrate_pages()
+-------------------------
+
+1. Remove pages from the LRU.
+
+   Lists of pages to be migrated are generated by scanning over
+   pages and moving them into lists. This is done by
+   calling isolate_lru_page() or __isolate_lru_page().
+   Calling isolate_lru_page increases the references to the page
+   so that it cannot vanish under us.
+
+2. Generate a list of newly allocates page to move the contents
+   of the first list to.
+
+3. The migrate_pages() function is called which attempts
+   to do the migration. It returns the moved pages in the
+   list specified as the third parameter and the failed
+   migrations in the fourth parameter. The first parameter
+   will contain the pages that could still be retried.
+
+4. The leftover pages of various types are returned
+   to the LRU using putback_to_lru_pages() or otherwise
+   disposed of. The pages will still have the refcount as
+   increased by isolate_lru_pages()!
+
+B. Operation of migrate_pages()
+--------------------------------
+
+migrate_pages does several passes over its list of pages. A page is moved
+if all references to a page are removable at the time.
+
+Steps:
+
+1. Lock the page to be migrated
+
+2. Insure that writeback is complete.
+
+3. Make sure that the page has assigned swap cache entry if
+   it is an anonyous page. The swap cache reference is necessary
+   to preserve the information contain in the page table maps.
+
+4. Prep the new page that we want to move to. It is locked
+   and set to not being uptodate so that all accesses to the new
+   page immediately lock while we are moving references.
+
+5. All the page table references to the page are either dropped (file backed)
+   or converted to swap references (anonymous pages). This should decrease the
+   reference count.
+
+6. The radix tree lock is taken
+
+7. The refcount of the page is examined and we back out if references remain
+   otherwise we know that we are the only one referencing this page.
+
+8. The radix tree is checked and if it does not contain the pointer to this
+   page then we back out.
+
+9. The mapping is checked. If the mapping is gone then a truncate action may
+   be in progress and we back out.
+
+10. The new page is prepped with some settings from the old page so that accesses
+   to the new page will be discovered to have the correct settings.
+
+11. The radix tree is changed to point to the new page.
+
+12. The reference count of the old page is dropped because the reference has now
+    been removed.
+
+13. The radix tree lock is dropped.
+
+14. The page contents are copied to the new page.
+
+15. The remaining page flags are copied to the new page.
+
+16. The old page flags are cleared to indicate that the page does
+    not use any information anymore.
+
+17. Queued up writeback on the new page is triggered.
+
+18. If swap pte's were generated for the page then remove them again.
+
+19. The locks are dropped from the old and new page.
+
+20. The new page is moved to the LRU.
+
+Christoph Lameter, December 19, 2005.
+
diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 9d6fbeef2104..0f1ea2d6ed86 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -91,7 +91,7 @@ static inline void page_dup_rmap(struct page *page)
  * Called from mm/vmscan.c to handle paging out
  */
 int page_referenced(struct page *, int is_locked);
-int try_to_unmap(struct page *);
+int try_to_unmap(struct page *, int ignore_refs);
 
 /*
  * Called from mm/filemap_xip.c to unmap empty zero page
@@ -111,7 +111,7 @@ unsigned long page_address_in_vma(struct page *, struct vm_area_struct *);
 #define anon_vma_link(vma)      do {} while (0)
 
 #define page_referenced(page,l) TestClearPageReferenced(page)
-#define try_to_unmap(page)      SWAP_FAIL
+#define try_to_unmap(page, refs) SWAP_FAIL
 
 #endif  /* CONFIG_MMU */
 
diff --git a/include/linux/swap.h b/include/linux/swap.h
index e53fef7051e6..d359fc022433 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -191,6 +191,8 @@ static inline int zone_reclaim(struct zone *z, gfp_t mask, unsigned int order)
 #ifdef CONFIG_MIGRATION
 extern int isolate_lru_page(struct page *p);
 extern int putback_lru_pages(struct list_head *l);
+extern int migrate_page(struct page *, struct page *);
+extern void migrate_page_copy(struct page *, struct page *);
 extern int migrate_pages(struct list_head *l, struct list_head *t,
                 struct list_head *moved, struct list_head *failed);
 #else
diff --git a/mm/rmap.c b/mm/rmap.c
index d85a99d28c03..13fad5fcdf79 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -52,6 +52,7 @@
 #include <linux/init.h>
 #include <linux/rmap.h>
 #include <linux/rcupdate.h>
+#include <linux/module.h>
 
 #include <asm/tlbflush.h>
 
@@ -541,7 +542,8 @@ void page_remove_rmap(struct page *page)
  * Subfunctions of try_to_unmap: try_to_unmap_one called
  * repeatedly from either try_to_unmap_anon or try_to_unmap_file.
  */
-static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma)
+static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
+                                int ignore_refs)
 {
         struct mm_struct *mm = vma->vm_mm;
         unsigned long address;
@@ -564,7 +566,8 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma)
          * skipped over this mm) then we should reactivate it.
          */
         if ((vma->vm_flags & VM_LOCKED) ||
-                        ptep_clear_flush_young(vma, address, pte)) {
+                        (ptep_clear_flush_young(vma, address, pte)
+                                && !ignore_refs)) {
                 ret = SWAP_FAIL;
                 goto out_unmap;
         }
@@ -698,7 +701,7 @@ static void try_to_unmap_cluster(unsigned long cursor,
         pte_unmap_unlock(pte - 1, ptl);
 }
 
-static int try_to_unmap_anon(struct page *page)
+static int try_to_unmap_anon(struct page *page, int ignore_refs)
 {
         struct anon_vma *anon_vma;
         struct vm_area_struct *vma;
@@ -709,7 +712,7 @@ static int try_to_unmap_anon(struct page *page)
                 return ret;
 
         list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
-                ret = try_to_unmap_one(page, vma);
+                ret = try_to_unmap_one(page, vma, ignore_refs);
                 if (ret == SWAP_FAIL || !page_mapped(page))
                         break;
         }
@@ -726,7 +729,7 @@ static int try_to_unmap_anon(struct page *page)
  *
  * This function is only called from try_to_unmap for object-based pages.
  */
-static int try_to_unmap_file(struct page *page)
+static int try_to_unmap_file(struct page *page, int ignore_refs)
 {
         struct address_space *mapping = page->mapping;
         pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
@@ -740,7 +743,7 @@ static int try_to_unmap_file(struct page *page)
 
         spin_lock(&mapping->i_mmap_lock);
         vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
-                ret = try_to_unmap_one(page, vma);
+                ret = try_to_unmap_one(page, vma, ignore_refs);
                 if (ret == SWAP_FAIL || !page_mapped(page))
                         goto out;
         }
@@ -825,16 +828,16 @@ out:
  * SWAP_AGAIN   - we missed a mapping, try again later
  * SWAP_FAIL    - the page is unswappable
  */
-int try_to_unmap(struct page *page)
+int try_to_unmap(struct page *page, int ignore_refs)
 {
         int ret;
 
         BUG_ON(!PageLocked(page));
 
         if (PageAnon(page))
-                ret = try_to_unmap_anon(page);
+                ret = try_to_unmap_anon(page, ignore_refs);
         else
-                ret = try_to_unmap_file(page);
+                ret = try_to_unmap_file(page, ignore_refs);
 
         if (!page_mapped(page))
                 ret = SWAP_SUCCESS;
diff --git a/mm/vmscan.c b/mm/vmscan.c
index aa4b80dbe3ad..8f326ce2b690 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -483,7 +483,7 @@ static int shrink_list(struct list_head *page_list, struct scan_control *sc)
                         if (!sc->may_swap)
                                 goto keep_locked;
 
-                        switch (try_to_unmap(page)) {
+                        switch (try_to_unmap(page, 0)) {
                         case SWAP_FAIL:
                                 goto activate_locked;
                         case SWAP_AGAIN:
@@ -623,7 +623,7 @@ static int swap_page(struct page *page)
         struct address_space *mapping = page_mapping(page);
 
         if (page_mapped(page) && mapping)
-                if (try_to_unmap(page) != SWAP_SUCCESS)
+                if (try_to_unmap(page, 0) != SWAP_SUCCESS)
                         goto unlock_retry;
 
         if (PageDirty(page)) {
@@ -659,6 +659,154 @@ unlock_retry:
 retry:
         return -EAGAIN;
 }
+
+/*
+ * 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>
+ */
+
+/*
+ * Remove references for a page and establish the new page with the correct
+ * basic settings to be able to stop accesses to the page.
+ */
+static 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 1;
+
+        /*
+         * 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.
+         */
+        try_to_unmap(page, 1);
+
+        /*
+         * Give up if we were unable to remove all mappings.
+         */
+        if (page_mapcount(page))
+                return 1;
+
+        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 1;
+        }
+
+        /*
+         * 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;
+}
+
+/*
+ * 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);
+}
+
+/*
+ * 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)
+{
+        BUG_ON(PageWriteback(page));    /* Writeback must be complete */
+
+        if (migrate_page_remove_references(newpage, page, 2))
+                return -EAGAIN;
+
+        migrate_page_copy(newpage, page);
+
+        return 0;
+}
+
 /*
  * migrate_pages
  *
@@ -672,11 +820,6 @@ retry:
  * are movable anymore because t has become empty
  * or no retryable pages exist anymore.
  *
- * SIMPLIFIED VERSION: This implementation of migrate_pages
- * is only swapping out pages and never touches the second
- * list. The direct migration patchset
- * extends this function to avoid the use of swap.
- *
  * Return: Number of pages not migrated when "to" ran empty.
  */
 int migrate_pages(struct list_head *from, struct list_head *to,
@@ -697,6 +840,9 @@ redo:
         retry = 0;
 
         list_for_each_entry_safe(page, page2, from, lru) {
+                struct page *newpage = NULL;
+                struct address_space *mapping;
+
                 cond_resched();
 
                 rc = 0;
@@ -704,6 +850,9 @@ redo:
                         /* 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
@@ -740,12 +889,64 @@ redo:
                         }
                 }
 
+                if (!to) {
+                        rc = swap_page(page);
+                        goto next;
+                }
+
+                newpage = lru_to_page(to);
+                lock_page(newpage);
+
                 /*
-                 * Page is properly locked and writeback is complete.
+                 * Pages are properly locked and writeback is complete.
                  * Try to migrate the page.
                  */
-                rc = swap_page(page);
-                goto next;
+                mapping = page_mapping(page);
+                if (!mapping)
+                        goto unlock_both;
+
+                /*
+                 * Trigger writeout if page is dirty
+                 */
+                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 */
+                        }
+                }
+                /*
+                 * If we have no buffer or can release the buffer
+                 * then do a simple migration.
+                 */
+                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) {
+                        unlock_page(newpage);
+                        newpage = NULL;
+                        rc = swap_page(page);
+                        goto next;
+                }
+
+unlock_both:
+                unlock_page(newpage);
 
 unlock_page:
                 unlock_page(page);
@@ -758,7 +959,10 @@ next:
                         list_move(&page->lru, failed);
                         nr_failed++;
                 } else {
-                        /* Success */
+                        if (newpage) {
+                                /* Successful migration. Return page to LRU */
+                                move_to_lru(newpage);
+                        }
                         list_move(&page->lru, moved);
                 }
         }