Commit 32f51ead authored by Matthew Wilcox (Oracle)'s avatar Matthew Wilcox (Oracle) Committed by Andrew Morton
Browse files

mm: remove PageSwapCache 

This flag is now only used on folios, so we can remove all the page
accessors and reword the comments that refer to them.

Link: https://lkml.kernel.org/r/20240821193445.2294269-5-willy@infradead.org


Signed-off-by: default avatarMatthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 6f394ee9

include/linux/mm_types.h

+1 −1
Original line number Diff line number Diff line
@@ -109,7 +109,7 @@ struct page { 
			/**

			 * @private: Mapping-private opaque data.

			 * Usually used for buffer_heads if PagePrivate.

			 * Used for swp_entry_t if PageSwapCache.

			 * Used for swp_entry_t if swapcache flag set.

			 * Indicates order in the buddy system if PageBuddy.

			 */

			unsigned long private;

include/linux/page-flags.h

+3 −8
Original line number Diff line number Diff line
@@ -574,15 +574,10 @@ static __always_inline bool folio_test_swapcache(const struct folio *folio) 
			test_bit(PG_swapcache, const_folio_flags(folio, 0));

}



static __always_inline bool PageSwapCache(const struct page *page)

{

	return folio_test_swapcache(page_folio(page));

}



SETPAGEFLAG(SwapCache, swapcache, PF_NO_TAIL)

CLEARPAGEFLAG(SwapCache, swapcache, PF_NO_TAIL)

FOLIO_SET_FLAG(swapcache, FOLIO_HEAD_PAGE)

FOLIO_CLEAR_FLAG(swapcache, FOLIO_HEAD_PAGE)

#else

PAGEFLAG_FALSE(SwapCache, swapcache)

FOLIO_FLAG_FALSE(swapcache)

#endif



PAGEFLAG(Unevictable, unevictable, PF_HEAD)

mm/ksm.c

+10 −9
Original line number Diff line number Diff line
@@ -909,12 +909,13 @@ static struct folio *ksm_get_folio(struct ksm_stable_node *stable_node, 
	 */

	while (!folio_try_get(folio)) {

		/*

		 * Another check for page->mapping != expected_mapping would

		 * work here too.  We have chosen the !PageSwapCache test to

		 * optimize the common case, when the page is or is about to

		 * be freed: PageSwapCache is cleared (under spin_lock_irq)

		 * in the ref_freeze section of __remove_mapping(); but Anon

		 * folio->mapping reset to NULL later, in free_pages_prepare().

		 * Another check for folio->mapping != expected_mapping

		 * would work here too.  We have chosen to test the

		 * swapcache flag to optimize the common case, when the

		 * folio is or is about to be freed: the swapcache flag

		 * is cleared (under spin_lock_irq) in the ref_freeze

		 * section of __remove_mapping(); but anon folio->mapping

		 * is reset to NULL later, in free_pages_prepare().

		 */

		if (!folio_test_swapcache(folio))

			goto stale;
@@ -945,7 +946,7 @@ static struct folio *ksm_get_folio(struct ksm_stable_node *stable_node, 


stale:

	/*

	 * We come here from above when page->mapping or !PageSwapCache

	 * We come here from above when folio->mapping or the swapcache flag

	 * suggests that the node is stale; but it might be under migration.

	 * We need smp_rmb(), matching the smp_wmb() in folio_migrate_ksm(),

	 * before checking whether node->kpfn has been changed.
@@ -1452,7 +1453,7 @@ static int try_to_merge_one_page(struct vm_area_struct *vma, 
		goto out;



	/*

	 * We need the page lock to read a stable PageSwapCache in

	 * We need the folio lock to read a stable swapcache flag in

	 * write_protect_page().  We use trylock_page() instead of

	 * lock_page() because we don't want to wait here - we

	 * prefer to continue scanning and merging different pages,
@@ -3123,7 +3124,7 @@ void folio_migrate_ksm(struct folio *newfolio, struct folio *folio) 
		 * newfolio->mapping was set in advance; now we need smp_wmb()

		 * to make sure that the new stable_node->kpfn is visible

		 * to ksm_get_folio() before it can see that folio->mapping

		 * has gone stale (or that folio_test_swapcache has been cleared).

		 * has gone stale (or that the swapcache flag has been cleared).

		 */

		smp_wmb();

		folio_set_stable_node(folio, NULL);

mm/migrate.c

+2 −1
Original line number Diff line number Diff line
@@ -639,7 +639,8 @@ void folio_migrate_flags(struct folio *newfolio, struct folio *folio) 
	folio_migrate_ksm(newfolio, folio);

	/*

	 * Please do not reorder this without considering how mm/ksm.c's

	 * ksm_get_folio() depends upon ksm_migrate_page() and PageSwapCache().

	 * ksm_get_folio() depends upon ksm_migrate_page() and the

	 * swapcache flag.

	 */

	if (folio_test_swapcache(folio))

		folio_clear_swapcache(folio);

mm/shmem.c

+6 −5
Original line number Diff line number Diff line
@@ -502,8 +502,8 @@ static int shmem_replace_entry(struct address_space *mapping, 
 * Sometimes, before we decide whether to proceed or to fail, we must check

 * that an entry was not already brought back from swap by a racing thread.

 *

 * Checking page is not enough: by the time a SwapCache page is locked, it

 * might be reused, and again be SwapCache, using the same swap as before.

 * Checking folio is not enough: by the time a swapcache folio is locked, it

 * might be reused, and again be swapcache, using the same swap as before.

 */

static bool shmem_confirm_swap(struct address_space *mapping,

			       pgoff_t index, swp_entry_t swap)
@@ -1965,9 +1965,10 @@ static int shmem_replace_folio(struct folio **foliop, gfp_t gfp, 


	if (unlikely(error)) {

		/*

		 * Is this possible?  I think not, now that our callers check

		 * both PageSwapCache and page_private after getting page lock;

		 * but be defensive.  Reverse old to newpage for clear and free.

		 * Is this possible?  I think not, now that our callers

		 * check both the swapcache flag and folio->private

		 * after getting the folio lock; but be defensive.

		 * Reverse old to newpage for clear and free.

		 */

		old = new;

	} else {