Re: [PATCH 1/6] mm: migrate: add isolate_movable_folio()

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On 2024/3/28 2:59, Vishal Moola wrote:
On Wed, Mar 27, 2024 at 10:10:29PM +0800, Kefeng Wang wrote:
Like isolate_lru_page(), make isolate_movable_page() as a wrapper
around isolate_lru_folio(), since isolate_movable_page() always
fails on a tail page, add a warn for tail page and return immediately.

Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
---
  include/linux/migrate.h |  3 +++
  mm/migrate.c            | 41 +++++++++++++++++++++++------------------
  2 files changed, 26 insertions(+), 18 deletions(-)

diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index f9d92482d117..a6c38ee7246a 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -70,6 +70,7 @@ int migrate_pages(struct list_head *l, new_folio_t new, free_folio_t free,
  		  unsigned int *ret_succeeded);
  struct folio *alloc_migration_target(struct folio *src, unsigned long private);
  bool isolate_movable_page(struct page *page, isolate_mode_t mode);
+bool isolate_movable_folio(struct folio *folio, isolate_mode_t mode);
int migrate_huge_page_move_mapping(struct address_space *mapping,
  		struct folio *dst, struct folio *src);
@@ -91,6 +92,8 @@ static inline struct folio *alloc_migration_target(struct folio *src,
  	{ return NULL; }
  static inline bool isolate_movable_page(struct page *page, isolate_mode_t mode)
  	{ return false; }
+static inline bool isolate_movable_folio(struct page *page, isolate_mode_t mode)
+	{ return false; }

Wrong argument here.
Mistake, will fix.


static inline int migrate_huge_page_move_mapping(struct address_space *mapping,
  				  struct folio *dst, struct folio *src)
diff --git a/mm/migrate.c b/mm/migrate.c
index 2228ca681afb..b2195b6ff32c 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -57,31 +57,29 @@
#include "internal.h" -bool isolate_movable_page(struct page *page, isolate_mode_t mode)
+bool isolate_movable_folio(struct folio *folio, isolate_mode_t mode)
  {
-	struct folio *folio = folio_get_nontail_page(page);
  	const struct movable_operations *mops;
/*
-	 * Avoid burning cycles with pages that are yet under __free_pages(),
+	 * Avoid burning cycles with folios that are yet under __free_pages(),
  	 * or just got freed under us.
  	 *
-	 * In case we 'win' a race for a movable page being freed under us and
+	 * In case we 'win' a race for a movable folio being freed under us and
  	 * raise its refcount preventing __free_pages() from doing its job
-	 * the put_page() at the end of this block will take care of
-	 * release this page, thus avoiding a nasty leakage.
+	 * the folio_put() at the end of this block will take care of
+	 * release this folio, thus avoiding a nasty leakage.
  	 */
-	if (!folio)
-		goto out;
+	folio_get(folio);
if (unlikely(folio_test_slab(folio)))
  		goto out_putfolio;
  	/* Pairs with smp_wmb() in slab freeing, e.g. SLUB's __free_slab() */
  	smp_rmb();
  	/*
-	 * Check movable flag before taking the page lock because
-	 * we use non-atomic bitops on newly allocated page flags so
-	 * unconditionally grabbing the lock ruins page's owner side.
+	 * Check movable flag before taking the folio lock because
+	 * we use non-atomic bitops on newly allocated folio flags so
+	 * unconditionally grabbing the lock ruins folio's owner side.
  	 */
  	if (unlikely(!__folio_test_movable(folio)))
  		goto out_putfolio;
@@ -91,13 +89,13 @@ bool isolate_movable_page(struct page *page, isolate_mode_t mode)
  		goto out_putfolio;
/*
-	 * As movable pages are not isolated from LRU lists, concurrent
-	 * compaction threads can race against page migration functions
-	 * as well as race against the releasing a page.
+	 * As movable folios are not isolated from LRU lists, concurrent
+	 * compaction threads can race against folio migration functions
+	 * as well as race against the releasing a folio.
  	 *
-	 * In order to avoid having an already isolated movable page
+	 * In order to avoid having an already isolated movable folio
  	 * being (wrongly) re-isolated while it is under migration,
-	 * or to avoid attempting to isolate pages being released,
+	 * or to avoid attempting to isolate folios being released,
  	 * lets be sure we have the page lock
  	 * before proceeding with the movable page isolation steps.
  	 */
@@ -113,7 +111,7 @@ bool isolate_movable_page(struct page *page, isolate_mode_t mode)
  	if (!mops->isolate_page(&folio->page, mode))
  		goto out_no_isolated;
- /* Driver shouldn't use PG_isolated bit of page->flags */
+	/* Driver shouldn't use PG_isolated bit of folio->flags */
  	WARN_ON_ONCE(folio_test_isolated(folio));
  	folio_set_isolated(folio);
  	folio_unlock(folio);
@@ -124,10 +122,17 @@ bool isolate_movable_page(struct page *page, isolate_mode_t mode)
  	folio_unlock(folio);
  out_putfolio:
  	folio_put(folio);
-out:
  	return false;
  }
+bool isolate_movable_page(struct page *page, isolate_mode_t mode)
+{
+	if (WARN_RATELIMIT(PageTail(page), "trying to isolate tail page"))
+		return false;

This warning doesn't make sense. As of now, we still isolate_movable_page()
to be able to take in a tail page, we just don't want to operate on it.
Zi replied too, I will remove it.

Thanks.

+	return isolate_movable_folio((struct folio *)page, mode);
+}
+
  static void putback_movable_folio(struct folio *folio)
  {
  	const struct movable_operations *mops = folio_movable_ops(folio);
--
2.27.0





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