Re: [RFCv3 2/5] mm/compaction: enable mobile-page migration

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@@ -51,6 +54,66 @@ extern void compaction_defer_reset(struct zone *zone, int order,
                                 bool alloc_success);
  extern bool compaction_restarting(struct zone *zone, int order);

+static inline bool mobile_page(struct page *page)
+{
+       return page->mapping && page->mapping->a_ops &&

Dereferncing mapping->a_ops isn't safe without page-lock and isn't required:
all mappings always have ->a_ops.


I got it.

+static inline void putback_mobilepage(struct page *page)
+{
+       /*
+        * 'lock_page()' stabilizes the page and prevents races against
+        * concurrent isolation threads attempting to re-isolate it.
+        */
+       lock_page(page);
+       if (mobile_page(page) && page->mapping->a_ops->putbackpage) {

It seems "if (page->mapping && page->mapping->a_ops->putbackpage)"
should be enough: we already seen that page as mobile.

Ditto.


+               page->mapping->a_ops->putbackpage(page);
+               /* drop the extra ref count taken for mobile page isolation */
+               put_page(page);
+       }
+       unlock_page(page);

call put_page() after unlock and do that always -- putback must drop
page reference from caller.

lock_page(page);
if (page->mapping && page->mapping->a_ops->putbackpage)
      page->mapping->a_ops->putbackpage(page);
unlock_page();
put_page(page);


Ditto.

+}
  #else
  static inline unsigned long try_to_compact_pages(gfp_t gfp_mask,
                         unsigned int order, int alloc_flags,
@@ -83,6 +146,19 @@ static inline bool compaction_deferred(struct zone *zone, int order)
         return true;
  }

+static inline bool mobile_page(struct page *page)
+{
+       return false;
+}
+
+static inline bool isolate_mobilepage(struct page *page, isolate_mode_t mode)
+{
+       return false;
+}
+
+static inline void putback_mobilepage(struct page *page)
+{
+}
  #endif /* CONFIG_COMPACTION */

  #if defined(CONFIG_COMPACTION) && defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 35ec87e..33c9aa5 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -395,6 +395,8 @@ struct address_space_operations {
          */
         int (*migratepage) (struct address_space *,
                         struct page *, struct page *, enum migrate_mode);
+       bool (*isolatepage) (struct page *, isolate_mode_t);
+       void (*putbackpage) (struct page *);
         int (*launder_page) (struct page *);
         int (*is_partially_uptodate) (struct page *, unsigned long,
                                         unsigned long);
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index f34e040..abef145 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -582,6 +582,25 @@ static inline void __ClearPageBalloon(struct page *page)
         atomic_set(&page->_mapcount, -1);
  }

+#define PAGE_MOBILE_MAPCOUNT_VALUE (-255)
+
+static inline int PageMobile(struct page *page)
+{
+       return atomic_read(&page->_mapcount) == PAGE_MOBILE_MAPCOUNT_VALUE;
+}
+
+static inline void __SetPageMobile(struct page *page)
+{
+       VM_BUG_ON_PAGE(atomic_read(&page->_mapcount) != -1, page);
+       atomic_set(&page->_mapcount, PAGE_MOBILE_MAPCOUNT_VALUE);
+}
+
+static inline void __ClearPageMobile(struct page *page)
+{
+       VM_BUG_ON_PAGE(!PageMobile(page), page);
+       atomic_set(&page->_mapcount, -1);
+}
+
  /*
   * If network-based swap is enabled, sl*b must keep track of whether pages
   * were allocated from pfmemalloc reserves.
diff --git a/include/uapi/linux/kernel-page-flags.h b/include/uapi/linux/kernel-page-flags.h
index a6c4962..d50d9e8 100644
--- a/include/uapi/linux/kernel-page-flags.h
+++ b/include/uapi/linux/kernel-page-flags.h
@@ -33,6 +33,7 @@
  #define KPF_THP                        22
  #define KPF_BALLOON            23
  #define KPF_ZERO_PAGE          24
+#define KPF_MOBILE             25


  #endif /* _UAPILINUX_KERNEL_PAGE_FLAGS_H */
--
2.1.4



I fixed the code as your comments and I found patch 3/5 and 4/5 could not be applied separately.
So I merge them and report new [PATCH].
I appreciate your reviews.

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