mm/filemap: remove hugetlb special casing in filemap.c

Remove special cased hugetlb handling code within the page cache by
changing the granularity of ->index to the base page size rather than the
huge page size.  The motivation of this patch is to reduce complexity
within the filemap code while also increasing performance by removing
branches that are evaluated on every page cache lookup.

To support the change in index, new wrappers for hugetlb page cache
interactions are added.  These wrappers perform the conversion to a linear
index which is now expected by the page cache for huge pages.

========================= PERFORMANCE ======================================

Perf was used to check the performance differences after the patch. 
Overall the performance is similar to mainline with a very small larger
overhead that occurs in __filemap_add_folio() and
hugetlb_add_to_page_cache().  This is because of the larger overhead that
occurs in xa_load() and xa_store() as the xarray is now using more entries
to store hugetlb folios in the page cache.

Timing

aarch64
    2MB Page Size
        6.5-rc3 + this patch:
            [root@sidhakum-ol9-1 hugepages]# time fallocate -l 700GB test.txt
            real    1m49.568s
            user    0m0.000s
            sys     1m49.461s

        6.5-rc3:
            [root]# time fallocate -l 700GB test.txt
            real    1m47.495s
            user    0m0.000s
            sys     1m47.370s
    1GB Page Size
        6.5-rc3 + this patch:
            [root@sidhakum-ol9-1 hugepages1G]# time fallocate -l 700GB test.txt
            real    1m47.024s
            user    0m0.000s
            sys     1m46.921s

        6.5-rc3:
            [root@sidhakum-ol9-1 hugepages1G]# time fallocate -l 700GB test.txt
            real    1m44.551s
            user    0m0.000s
            sys     1m44.438s

x86
    2MB Page Size
        6.5-rc3 + this patch:
            [root@sidhakum-ol9-2 hugepages]# time fallocate -l 100GB test.txt
            real    0m22.383s
            user    0m0.000s
            sys     0m22.255s

        6.5-rc3:
            [opc@sidhakum-ol9-2 hugepages]$ time sudo fallocate -l 100GB /dev/hugepages/test.txt
            real    0m22.735s
            user    0m0.038s
            sys     0m22.567s

    1GB Page Size
        6.5-rc3 + this patch:
            [root@sidhakum-ol9-2 hugepages1GB]# time fallocate -l 100GB test.txt
            real    0m25.786s
            user    0m0.001s
            sys     0m25.589s

        6.5-rc3:
            [root@sidhakum-ol9-2 hugepages1G]# time fallocate -l 100GB test.txt
            real    0m33.454s
            user    0m0.001s
            sys     0m33.193s

aarch64:
    workload - fallocate a 700GB file backed by huge pages

    6.5-rc3 + this patch:
        2MB Page Size:
            --100.00%--__arm64_sys_fallocate
                          ksys_fallocate
                          vfs_fallocate
                          hugetlbfs_fallocate
                          |
                          |--95.04%--__pi_clear_page
                          |
                          |--3.57%--clear_huge_page
                          |          |
                          |          |--2.63%--rcu_all_qs
                          |          |
                          |           --0.91%--__cond_resched
                          |
                           --0.67%--__cond_resched
            0.17%     0.00%             0  fallocate  [kernel.vmlinux]       [k] hugetlb_add_to_page_cache
            0.14%     0.10%            11  fallocate  [kernel.vmlinux]       [k] __filemap_add_folio

    6.5-rc3
        2MB Page Size:
                --100.00%--__arm64_sys_fallocate
                          ksys_fallocate
                          vfs_fallocate
                          hugetlbfs_fallocate
                          |
                          |--94.91%--__pi_clear_page
                          |
                          |--4.11%--clear_huge_page
                          |          |
                          |          |--3.00%--rcu_all_qs
                          |          |
                          |           --1.10%--__cond_resched
                          |
                           --0.59%--__cond_resched
            0.08%     0.01%             1  fallocate  [kernel.kallsyms]  [k] hugetlb_add_to_page_cache
            0.05%     0.03%             3  fallocate  [kernel.kallsyms]  [k] __filemap_add_folio

x86
    workload - fallocate a 100GB file backed by huge pages

    6.5-rc3 + this patch:
        2MB Page Size:
            hugetlbfs_fallocate
            |
            --99.57%--clear_huge_page
                |
                --98.47%--clear_page_erms
                    |
                    --0.53%--asm_sysvec_apic_timer_interrupt

            0.04%     0.04%             1  fallocate  [kernel.kallsyms]     [k] xa_load
            0.04%     0.00%             0  fallocate  [kernel.kallsyms]     [k] hugetlb_add_to_page_cache
            0.04%     0.00%             0  fallocate  [kernel.kallsyms]     [k] __filemap_add_folio
            0.04%     0.00%             0  fallocate  [kernel.kallsyms]     [k] xas_store

    6.5-rc3
        2MB Page Size:
                --99.93%--__x64_sys_fallocate
                          vfs_fallocate
                          hugetlbfs_fallocate
                          |
                           --99.38%--clear_huge_page
                                     |
                                     |--98.40%--clear_page_erms
                                     |
                                      --0.59%--__cond_resched
            0.03%     0.03%             1  fallocate  [kernel.kallsyms]  [k] __filemap_add_folio

========================= TESTING ======================================

This patch passes libhugetlbfs tests and LTP hugetlb tests

********** TEST SUMMARY
*                      2M
*                      32-bit 64-bit
*     Total testcases:   110    113
*             Skipped:     0      0
*                PASS:   107    113
*                FAIL:     0      0
*    Killed by signal:     3      0
*   Bad configuration:     0      0
*       Expected FAIL:     0      0
*     Unexpected PASS:     0      0
*    Test not present:     0      0
* Strange test result:     0      0
**********

    Done executing testcases.
    LTP Version:  20220527-178-g2761a81c4

page migration was also tested using Mike Kravetz's test program.[8]

[dan.carpenter@linaro.org: fix an NULL vs IS_ERR() bug]
  Link: https://lkml.kernel.org/r/1772c296-1417-486f-8eef-171af2192681@moroto.mountain
Link: https://lkml.kernel.org/r/20230926192017.98183-1-sidhartha.kumar@oracle.comSigned-off-by: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reported-and-tested-by: syzbot+c225dea486da4d5592bd@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=c225dea486da4d5592bd
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/hugetlbfs/inode.c

@@ -334,7 +334,7 @@ static ssize_t hugetlbfs_read_iter(struct kiocb *iocb, struct iov_iter *to)
 	ssize_t retval = 0;
 
 	while (iov_iter_count(to)) {
-		struct page *page;
+		struct folio *folio;
 		size_t nr, copied, want;
 
 		/* nr is the maximum number of bytes to copy from this page */
@@ -352,18 +352,18 @@ static ssize_t hugetlbfs_read_iter(struct kiocb *iocb, struct iov_iter *to)
 		}
 		nr = nr - offset;
 
-		/* Find the page */
-		page = find_lock_page(mapping, index);
-		if (unlikely(page == NULL)) {
+		/* Find the folio */
+		folio = filemap_lock_hugetlb_folio(h, mapping, index);
+		if (IS_ERR(folio)) {
 			/*
 			 * We have a HOLE, zero out the user-buffer for the
 			 * length of the hole or request.
 			 */
 			copied = iov_iter_zero(nr, to);
 		} else {
-			unlock_page(page);
+			folio_unlock(folio);
 
-			if (!PageHWPoison(page))
+			if (!folio_test_has_hwpoisoned(folio))
 				want = nr;
 			else {
 				/*
@@ -371,19 +371,19 @@ static ssize_t hugetlbfs_read_iter(struct kiocb *iocb, struct iov_iter *to)
 				 * touching the 1st raw HWPOISON subpage after
 				 * offset.
 				 */
-				want = adjust_range_hwpoison(page, offset, nr);
+				want = adjust_range_hwpoison(&folio->page, offset, nr);
 				if (want == 0) {
-					put_page(page);
+					folio_put(folio);
 					retval = -EIO;
 					break;
 				}
 			}
 
 			/*
-			 * We have the page, copy it to user space buffer.
+			 * We have the folio, copy it to user space buffer.
 			 */
-			copied = copy_page_to_iter(page, offset, want, to);
-			put_page(page);
+			copied = copy_folio_to_iter(folio, offset, want, to);
+			folio_put(folio);
 		}
 		offset += copied;
 		retval += copied;
@@ -661,21 +661,20 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart,
 {
 	struct hstate *h = hstate_inode(inode);
 	struct address_space *mapping = &inode->i_data;
-	const pgoff_t start = lstart >> huge_page_shift(h);
-	const pgoff_t end = lend >> huge_page_shift(h);
+	const pgoff_t end = lend >> PAGE_SHIFT;
 	struct folio_batch fbatch;
 	pgoff_t next, index;
 	int i, freed = 0;
 	bool truncate_op = (lend == LLONG_MAX);
 
 	folio_batch_init(&fbatch);
-	next = start;
+	next = lstart >> PAGE_SHIFT;
 	while (filemap_get_folios(mapping, &next, end - 1, &fbatch)) {
 		for (i = 0; i < folio_batch_count(&fbatch); ++i) {
 			struct folio *folio = fbatch.folios[i];
 			u32 hash = 0;
 
-			index = folio->index;
+			index = folio->index >> huge_page_order(h);
 			hash = hugetlb_fault_mutex_hash(mapping, index);
 			mutex_lock(&hugetlb_fault_mutex_table[hash]);
 
@@ -693,7 +692,9 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart,
 	}
 
 	if (truncate_op)
-		(void)hugetlb_unreserve_pages(inode, start, LONG_MAX, freed);
+		(void)hugetlb_unreserve_pages(inode,
+				lstart >> huge_page_shift(h),
+				LONG_MAX, freed);
 }
 
 static void hugetlbfs_evict_inode(struct inode *inode)
@@ -741,7 +742,7 @@ static void hugetlbfs_zero_partial_page(struct hstate *h,
 	pgoff_t idx = start >> huge_page_shift(h);
 	struct folio *folio;
 
-	folio = filemap_lock_folio(mapping, idx);
+	folio = filemap_lock_hugetlb_folio(h, mapping, idx);
 	if (IS_ERR(folio))
 		return;
 
@@ -886,7 +887,7 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset,
 		mutex_lock(&hugetlb_fault_mutex_table[hash]);
 
 		/* See if already present in mapping to avoid alloc/free */
-		folio = filemap_get_folio(mapping, index);
+		folio = filemap_get_folio(mapping, index << huge_page_order(h));
 		if (!IS_ERR(folio)) {
 			folio_put(folio);
 			mutex_unlock(&hugetlb_fault_mutex_table[hash]);

include/linux/hugetlb.h

@@ -812,6 +812,12 @@ static inline unsigned int blocks_per_huge_page(struct hstate *h)
 	return huge_page_size(h) / 512;
 }
 
+static inline struct folio *filemap_lock_hugetlb_folio(struct hstate *h,
+				struct address_space *mapping, pgoff_t idx)
+{
+	return filemap_lock_folio(mapping, idx << huge_page_order(h));
+}
+
 #include <asm/hugetlb.h>
 
 #ifndef is_hugepage_only_range
@@ -1008,6 +1014,12 @@ static inline struct hugepage_subpool *hugetlb_folio_subpool(struct folio *folio
 	return NULL;
 }
 
+static inline struct folio *filemap_lock_hugetlb_folio(struct hstate *h,
+				struct address_space *mapping, pgoff_t idx)
+{
+	return NULL;
+}
+
 static inline int isolate_or_dissolve_huge_page(struct page *page,
 						struct list_head *list)
 {

include/linux/pagemap.h

@@ -789,9 +789,6 @@ static inline pgoff_t folio_next_index(struct folio *folio)
  */
 static inline struct page *folio_file_page(struct folio *folio, pgoff_t index)
 {
-	/* HugeTLBfs indexes the page cache in units of hpage_size */
-	if (folio_test_hugetlb(folio))
-		return &folio->page;
 	return folio_page(folio, index & (folio_nr_pages(folio) - 1));
 }
 
@@ -807,9 +804,6 @@ 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);
 }
 
@@ -867,10 +861,9 @@ static inline struct folio *read_mapping_folio(struct address_space *mapping,
 }
 
 /*
- * Get index of the page within radix-tree (but not for hugetlb pages).
- * (TODO: remove once hugetlb pages will have ->index in PAGE_SIZE)
+ * Get the offset in PAGE_SIZE (even for hugetlb pages).
  */
-static inline pgoff_t page_to_index(struct page *page)
+static inline pgoff_t page_to_pgoff(struct page *page)
 {
 	struct page *head;
 
@@ -885,19 +878,6 @@ static inline pgoff_t page_to_index(struct page *page)
 	return head->index + page - head;
 }
 
-extern pgoff_t hugetlb_basepage_index(struct page *page);
-
-/*
- * Get the offset in PAGE_SIZE (even for hugetlb pages).
- * (TODO: hugetlb pages should have ->index in PAGE_SIZE)
- */
-static inline pgoff_t page_to_pgoff(struct page *page)
-{
-	if (unlikely(PageHuge(page)))
-		return hugetlb_basepage_index(page);
-	return page_to_index(page);
-}
-
 /*
  * Return byte-offset into filesystem object for page.
  */
@@ -934,24 +914,16 @@ 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;
 }
 
-extern pgoff_t linear_hugepage_index(struct vm_area_struct *vma,
-				     unsigned long address);
-
 static inline pgoff_t linear_page_index(struct vm_area_struct *vma,
 					unsigned long address)
 {
 	pgoff_t pgoff;
-	if (unlikely(is_vm_hugetlb_page(vma)))
-		return linear_hugepage_index(vma, address);
 	pgoff = (address - vma->vm_start) >> PAGE_SHIFT;
 	pgoff += vma->vm_pgoff;
 	return pgoff;

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;
@@ -2040,7 +2038,7 @@ 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;
 	}
@@ -2104,7 +2102,7 @@ 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;
 	}
@@ -2145,9 +2143,6 @@ 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;
 		}
@@ -2213,9 +2208,6 @@ 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;
 		}
@@ -2232,10 +2224,7 @@ 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_next_index(folio);
+		*start = folio->index + folio_nr_pages(folio);
 	}
 out:
 	rcu_read_unlock();
@@ -2273,9 +2262,6 @@ 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;
 		}

mm/hugetlb.c

@@ -952,7 +952,7 @@ static long region_count(struct resv_map *resv, long f, long t)
 
 /*
  * Convert the address within this vma to the page offset within
- * the mapping, in pagecache page units; huge pages here.
+ * the mapping, huge page units here.
  */
 static pgoff_t vma_hugecache_offset(struct hstate *h,
 			struct vm_area_struct *vma, unsigned long address)
@@ -961,13 +961,6 @@ static pgoff_t vma_hugecache_offset(struct hstate *h,
 			(vma->vm_pgoff >> huge_page_order(h));
 }
 
-pgoff_t linear_hugepage_index(struct vm_area_struct *vma,
-				     unsigned long address)
-{
-	return vma_hugecache_offset(hstate_vma(vma), vma, address);
-}
-EXPORT_SYMBOL_GPL(linear_hugepage_index);
-
 /**
  * vma_kernel_pagesize - Page size granularity for this VMA.
  * @vma: The user mapping.
@@ -2074,20 +2067,6 @@ struct address_space *hugetlb_page_mapping_lock_write(struct page *hpage)
 	return NULL;
 }
 
-pgoff_t hugetlb_basepage_index(struct page *page)
-{
-	struct page *page_head = compound_head(page);
-	pgoff_t index = page_index(page_head);
-	unsigned long compound_idx;
-
-	if (compound_order(page_head) > MAX_ORDER)
-		compound_idx = page_to_pfn(page) - page_to_pfn(page_head);
-	else
-		compound_idx = page - page_head;
-
-	return (index << compound_order(page_head)) + compound_idx;
-}
-
 static struct folio *alloc_buddy_hugetlb_folio(struct hstate *h,
 		gfp_t gfp_mask, int nid, nodemask_t *nmask,
 		nodemask_t *node_alloc_noretry)
@@ -5772,7 +5751,7 @@ static bool hugetlbfs_pagecache_present(struct hstate *h,
 			struct vm_area_struct *vma, unsigned long address)
 {
 	struct address_space *mapping = vma->vm_file->f_mapping;
-	pgoff_t idx = vma_hugecache_offset(h, vma, address);
+	pgoff_t idx = linear_page_index(vma, address);
 	struct folio *folio;
 
 	folio = filemap_get_folio(mapping, idx);
@@ -5789,6 +5768,7 @@ int hugetlb_add_to_page_cache(struct folio *folio, struct address_space *mapping
 	struct hstate *h = hstate_inode(inode);
 	int err;
 
+	idx <<= huge_page_order(h);
 	__folio_set_locked(folio);
 	err = __filemap_add_folio(mapping, folio, idx, GFP_KERNEL, NULL);
 
@@ -5896,7 +5876,7 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm,
 	 * before we get page_table_lock.
 	 */
 	new_folio = false;
-	folio = filemap_lock_folio(mapping, idx);
+	folio = filemap_lock_hugetlb_folio(h, mapping, idx);
 	if (IS_ERR(folio)) {
 		size = i_size_read(mapping->host) >> huge_page_shift(h);
 		if (idx >= size)
@@ -6205,7 +6185,7 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
 		/* Just decrements count, does not deallocate */
 		vma_end_reservation(h, vma, haddr);
 
-		pagecache_folio = filemap_lock_folio(mapping, idx);
+		pagecache_folio = filemap_lock_hugetlb_folio(h, mapping, idx);
 		if (IS_ERR(pagecache_folio))
 			pagecache_folio = NULL;
 	}
@@ -6338,7 +6318,7 @@ int hugetlb_mfill_atomic_pte(pte_t *dst_pte,
 
 	if (is_continue) {
 		ret = -EFAULT;
-		folio = filemap_lock_folio(mapping, idx);
+		folio = filemap_lock_hugetlb_folio(h, mapping, idx);
 		if (IS_ERR(folio))
 			goto out;
 		folio_in_pagecache = true;

mm/migrate.c

@@ -524,7 +524,7 @@ int migrate_huge_page_move_mapping(struct address_space *mapping,
 	int expected_count;
 
 	xas_lock_irq(&xas);
-	expected_count = 2 + folio_has_private(src);
+	expected_count = folio_expected_refs(mapping, src);
 	if (!folio_ref_freeze(src, expected_count)) {
 		xas_unlock_irq(&xas);
 		return -EAGAIN;
@@ -533,11 +533,11 @@ int migrate_huge_page_move_mapping(struct address_space *mapping,
 	dst->index = src->index;
 	dst->mapping = src->mapping;
 
-	folio_get(dst);
+	folio_ref_add(dst, folio_nr_pages(dst));
 
 	xas_store(&xas, dst);
 
-	folio_ref_unfreeze(src, expected_count - 1);
+	folio_ref_unfreeze(src, expected_count - folio_nr_pages(src));
 
 	xas_unlock_irq(&xas);