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From:   Sidhartha Kumar <sidhartha.kumar@oracle.com>
To:     linux-kernel@vger.kernel.org, linux-mm@kvack.org
Cc:     akpm@linux-foundation.org, songmuchun@bytedance.com,
        mike.kravetz@oracle.com, willy@infradead.org,
        Sidhartha Kumar <sidhartha.kumar@oracle.com>
Subject: [RFC PATCH 1/4] mm/filemap: remove hugetlb special casing in filemap.c
Date:   Thu, 13 Apr 2023 16:14:49 -0700
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This patch aims to remove special cased hugetlb handling code within the
page cache by changing the granularity of each index to the base page size
rather than the huge page size.

Signed-off-by: Sidhartha Kumar <sidhartha.kumar@oracle.com>
---
 include/linux/pagemap.h |  6 ------
 mm/filemap.c            | 36 +++++++++++-------------------------
 2 files changed, 11 insertions(+), 31 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index fdcd595d22944..330b1db913f5a 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -717,9 +717,6 @@ static inline struct page *folio_file_page(struct folio *folio, pgoff_t index)
  */
 static inline bool folio_contains(struct folio *folio, pgoff_t index)
 {
-	/* HugeTLBfs indexes the page cache in units of hpage_size */
-	if (folio_test_hugetlb(folio))
-		return folio->index == index;
 	return index - folio_index(folio) < folio_nr_pages(folio);
 }
 
@@ -844,12 +841,9 @@ static inline loff_t folio_file_pos(struct folio *folio)
 
 /*
  * Get the offset in PAGE_SIZE (even for hugetlb folios).
- * (TODO: hugetlb folios should have ->index in PAGE_SIZE)
  */
 static inline pgoff_t folio_pgoff(struct folio *folio)
 {
-	if (unlikely(folio_test_hugetlb(folio)))
-		return hugetlb_basepage_index(&folio->page);
 	return folio->index;
 }
 
diff --git a/mm/filemap.c b/mm/filemap.c
index a34abfe8c6543..fadc8ca9b9695 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -131,11 +131,8 @@ static void page_cache_delete(struct address_space *mapping,
 
 	mapping_set_update(&xas, mapping);
 
-	/* hugetlb pages are represented by a single entry in the xarray */
-	if (!folio_test_hugetlb(folio)) {
-		xas_set_order(&xas, folio->index, folio_order(folio));
-		nr = folio_nr_pages(folio);
-	}
+	xas_set_order(&xas, folio->index, folio_order(folio));
+	nr = folio_nr_pages(folio);
 
 	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
 
@@ -234,7 +231,7 @@ void filemap_free_folio(struct address_space *mapping, struct folio *folio)
 	if (free_folio)
 		free_folio(folio);
 
-	if (folio_test_large(folio) && !folio_test_hugetlb(folio))
+	if (folio_test_large(folio))
 		refs = folio_nr_pages(folio);
 	folio_put_refs(folio, refs);
 }
@@ -855,14 +852,15 @@ noinline int __filemap_add_folio(struct address_space *mapping,
 
 	if (!huge) {
 		int error = mem_cgroup_charge(folio, NULL, gfp);
-		VM_BUG_ON_FOLIO(index & (folio_nr_pages(folio) - 1), folio);
 		if (error)
 			return error;
 		charged = true;
-		xas_set_order(&xas, index, folio_order(folio));
-		nr = folio_nr_pages(folio);
 	}
 
+	VM_BUG_ON_FOLIO(index & (folio_nr_pages(folio) - 1), folio);
+	xas_set_order(&xas, index, folio_order(folio));
+	nr = folio_nr_pages(folio);
+
 	gfp &= GFP_RECLAIM_MASK;
 	folio_ref_add(folio, nr);
 	folio->mapping = mapping;
@@ -2069,7 +2067,7 @@ unsigned find_get_entries(struct address_space *mapping, pgoff_t *start,
 		int idx = folio_batch_count(fbatch) - 1;
 
 		folio = fbatch->folios[idx];
-		if (!xa_is_value(folio) && !folio_test_hugetlb(folio))
+		if (!xa_is_value(folio))
 			nr = folio_nr_pages(folio);
 		*start = indices[idx] + nr;
 	}
@@ -2133,7 +2131,7 @@ unsigned find_lock_entries(struct address_space *mapping, pgoff_t *start,
 		int idx = folio_batch_count(fbatch) - 1;
 
 		folio = fbatch->folios[idx];
-		if (!xa_is_value(folio) && !folio_test_hugetlb(folio))
+		if (!xa_is_value(folio))
 			nr = folio_nr_pages(folio);
 		*start = indices[idx] + nr;
 	}
@@ -2174,9 +2172,6 @@ unsigned filemap_get_folios(struct address_space *mapping, pgoff_t *start,
 			continue;
 		if (!folio_batch_add(fbatch, folio)) {
 			unsigned long nr = folio_nr_pages(folio);
-
-			if (folio_test_hugetlb(folio))
-				nr = 1;
 			*start = folio->index + nr;
 			goto out;
 		}
@@ -2202,7 +2197,7 @@ EXPORT_SYMBOL(filemap_get_folios);
 static inline
 bool folio_more_pages(struct folio *folio, pgoff_t index, pgoff_t max)
 {
-	if (!folio_test_large(folio) || folio_test_hugetlb(folio))
+	if (!folio_test_large(folio))
 		return false;
 	if (index >= max)
 		return false;
@@ -2252,9 +2247,6 @@ unsigned filemap_get_folios_contig(struct address_space *mapping,
 
 		if (!folio_batch_add(fbatch, folio)) {
 			nr = folio_nr_pages(folio);
-
-			if (folio_test_hugetlb(folio))
-				nr = 1;
 			*start = folio->index + nr;
 			goto out;
 		}
@@ -2271,10 +2263,7 @@ unsigned filemap_get_folios_contig(struct address_space *mapping,
 
 	if (nr) {
 		folio = fbatch->folios[nr - 1];
-		if (folio_test_hugetlb(folio))
-			*start = folio->index + 1;
-		else
-			*start = folio->index + folio_nr_pages(folio);
+		*start = folio->index + folio_nr_pages(folio);
 	}
 out:
 	rcu_read_unlock();
@@ -2312,9 +2301,6 @@ unsigned filemap_get_folios_tag(struct address_space *mapping, pgoff_t *start,
 			continue;
 		if (!folio_batch_add(fbatch, folio)) {
 			unsigned long nr = folio_nr_pages(folio);
-
-			if (folio_test_hugetlb(folio))
-				nr = 1;
 			*start = folio->index + nr;
 			goto out;
 		}
-- 
2.39.2