tmpfs: preliminary minor tidyups

Make a few cleanups in mm/shmem.c, before going on to complicate it.

shmem_alloc_page() will become more complicated: we can't afford to to
have that complication duplicated between a CONFIG_NUMA version and a
!CONFIG_NUMA version, so rearrange the #ifdef'ery there to yield a
single shmem_swapin() and a single shmem_alloc_page().

Yes, it's a shame to inflict the horrid pseudo-vma on non-NUMA
configurations, but eliminating it is a larger cleanup: I have an
alloc_pages_mpol() patchset not yet ready - mpol handling is subtle and
bug-prone, and changed yet again since my last version.

Move __SetPageLocked, __SetPageSwapBacked from shmem_getpage_gfp() to
shmem_alloc_page(): that SwapBacked flag will be useful in future, to
help to distinguish different cases appropriately.

And the SGP_DIRTY variant of SGP_CACHE is hard to understand and of
little use (IIRC it dates back to when shmem_getpage() returned the page
unlocked): kill it and do the necessary in shmem_file_read_iter().

But an arm64 build then complained that info may be uninitialized (where
shmem_getpage_gfp() deletes a freshly alloced page beyond eof), and
advancing to an "sgp <= SGP_CACHE" test jogged it back to reality.

Signed-off-by: Hugh Dickins <[e-mail]>
Cc: "Kirill A. Shutemov" <[e-mail]>
Cc: Andrea Arcangeli <[e-mail]>
Cc: Andres Lagar-Cavilla <[e-mail]>
Cc: Yang Shi <[e-mail]>
Cc: Ning Qu <[e-mail]>
Cc: Mel Gorman <[e-mail]>
Cc: Konstantin Khlebnikov <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/mempolicy.h

···
 {
 }
 
+static inline struct mempolicy *
+mpol_shared_policy_lookup(struct shared_policy *sp, unsigned long idx)
+{
+	return NULL;
+}
+
 #define vma_policy(vma) NULL
 
 static inline int

mm/shmem.c

···
 enum sgp_type {
 	SGP_READ,	/* don't exceed i_size, don't allocate page */
 	SGP_CACHE,	/* don't exceed i_size, may allocate page */
-	SGP_DIRTY,	/* like SGP_CACHE, but set new page dirty */
 	SGP_WRITE,	/* may exceed i_size, may allocate !Uptodate page */
 	SGP_FALLOC,	/* like SGP_WRITE, but make existing page Uptodate */
 };
···
 
 /*
  * ... whereas tmpfs objects are accounted incrementally as
- * pages are allocated, in order to allow huge sparse files.
+ * pages are allocated, in order to allow large sparse files.
  * shmem_getpage reports shmem_acct_block failure as -ENOSPC not -ENOMEM,
  * so that a failure on a sparse tmpfs mapping will give SIGBUS not OOM.
  */
···
 	return 0;
 }
 
-#ifdef CONFIG_NUMA
-#ifdef CONFIG_TMPFS
+#if defined(CONFIG_NUMA) && defined(CONFIG_TMPFS)
 static void shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol)
 {
 	char buffer[64];
···
 	}
 	return mpol;
 }
-#endif /* CONFIG_TMPFS */
+#else /* !CONFIG_NUMA || !CONFIG_TMPFS */
+static inline void shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol)
+{
+}
+static inline struct mempolicy *shmem_get_sbmpol(struct shmem_sb_info *sbinfo)
+{
+	return NULL;
+}
+#endif /* CONFIG_NUMA && CONFIG_TMPFS */
+#ifndef CONFIG_NUMA
+#define vm_policy vm_private_data
+#endif
 
 static struct page *shmem_swapin(swp_entry_t swap, gfp_t gfp,
 			struct shmem_inode_info *info, pgoff_t index)
···
 	pvma.vm_ops = NULL;
 	pvma.vm_policy = mpol_shared_policy_lookup(&info->policy, index);
 
-	page = alloc_page_vma(gfp, &pvma, 0);
+	page = alloc_pages_vma(gfp, 0, &pvma, 0, numa_node_id(), false);
+	if (page) {
+		__SetPageLocked(page);
+		__SetPageSwapBacked(page);
+	}
 
 	/* Drop reference taken by mpol_shared_policy_lookup() */
 	mpol_cond_put(pvma.vm_policy);
 
 	return page;
 }
-#else /* !CONFIG_NUMA */
-#ifdef CONFIG_TMPFS
-static inline void shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol)
-{
-}
-#endif /* CONFIG_TMPFS */
-
-static inline struct page *shmem_swapin(swp_entry_t swap, gfp_t gfp,
-			struct shmem_inode_info *info, pgoff_t index)
-{
-	return swapin_readahead(swap, gfp, NULL, 0);
-}
-
-static inline struct page *shmem_alloc_page(gfp_t gfp,
-			struct shmem_inode_info *info, pgoff_t index)
-{
-	return alloc_page(gfp);
-}
-#endif /* CONFIG_NUMA */
-
-#if !defined(CONFIG_NUMA) || !defined(CONFIG_TMPFS)
-static inline struct mempolicy *shmem_get_sbmpol(struct shmem_sb_info *sbinfo)
-{
-	return NULL;
-}
-#endif
 
 /*
  * When a page is moved from swapcache to shmem filecache (either by the
···
 	copy_highpage(newpage, oldpage);
 	flush_dcache_page(newpage);
 
-	__SetPageLocked(newpage);
-	__SetPageSwapBacked(newpage);
 	SetPageUptodate(newpage);
 	set_page_private(newpage, swap_index);
 	SetPageSwapCache(newpage);
···
 		page = NULL;
 	}
 
-	if (sgp != SGP_WRITE && sgp != SGP_FALLOC &&
+	if (sgp <= SGP_CACHE &&
 	    ((loff_t)index << PAGE_SHIFT) >= i_size_read(inode)) {
 		error = -EINVAL;
 		goto unlock;
···
 			error = -ENOMEM;
 			goto decused;
 		}
-
-		__SetPageLocked(page);
-		__SetPageSwapBacked(page);
 		if (sgp == SGP_WRITE)
 			__SetPageReferenced(page);
 
···
 			flush_dcache_page(page);
 			SetPageUptodate(page);
 		}
-		if (sgp == SGP_DIRTY)
-			set_page_dirty(page);
 	}
 
 	/* Perhaps the file has been truncated since we checked */
-	if (sgp != SGP_WRITE && sgp != SGP_FALLOC &&
+	if (sgp <= SGP_CACHE &&
 	    ((loff_t)index << PAGE_SHIFT) >= i_size_read(inode)) {
 		if (alloced) {
 			ClearPageDirty(page);
···
 	 * and even mark them dirty, so it cannot exceed the max_blocks limit.
 	 */
 	if (!iter_is_iovec(to))
-		sgp = SGP_DIRTY;
+		sgp = SGP_CACHE;
 
 	index = *ppos >> PAGE_SHIFT;
 	offset = *ppos & ~PAGE_MASK;
···
 				error = 0;
 			break;
 		}
-		if (page)
+		if (page) {
+			if (sgp == SGP_CACHE)
+				set_page_dirty(page);
 			unlock_page(page);
+		}
 
 		/*
 		 * We must evaluate after, since reads (unlike writes)