filemap: add filemap_map_folio_range()

filemap_map_folio_range() maps partial/full folio.  Comparing to original
filemap_map_pages(), it updates refcount once per folio instead of per
page and gets minor performance improvement for large folio.

With a will-it-scale.page_fault3 like app (change file write fault testing
to read fault testing.  Trying to upstream it to will-it-scale at [1]),
got 2% performance gain on a 48C/96T Cascade Lake test box with 96
processes running against xfs.

[1]: https://github.com/antonblanchard/will-it-scale/pull/37

Link: https://lkml.kernel.org/r/20230802151406.3735276-35-willy@infradead.org
Signed-off-by: Yin Fengwei <fengwei.yin@intel.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/filemap.c b/mm/filemap.c
index 8040545954bc4175b26e1efd7331828a774333cd..bdc1e0b811bf0bc779547e1c2cf3ca8dd7ee5e0e 100644 (file)
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2168,16 +2168,6 @@ out:
 }
 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))
-               return false;
-       if (index >= max)
-               return false;
-       return index < folio_next_index(folio) - 1;
-}
-
 /**
  * filemap_get_folios_contig - Get a batch of contiguous folios
  * @mapping:   The address_space to search
@@ -3436,10 +3426,10 @@ static bool filemap_map_pmd(struct vm_fault *vmf, struct folio *folio,
        return false;
 }
 
-static struct folio *next_uptodate_page(struct folio *folio,
-                                      struct address_space *mapping,
-                                      struct xa_state *xas, pgoff_t end_pgoff)
+static struct folio *next_uptodate_folio(struct xa_state *xas,
+               struct address_space *mapping, pgoff_t end_pgoff)
 {
+       struct folio *folio = xas_next_entry(xas, end_pgoff);
        unsigned long max_idx;
 
        do {
@@ -3477,20 +3467,51 @@ skip:
        return NULL;
 }
 
-static inline struct folio *first_map_page(struct address_space *mapping,
-                                         struct xa_state *xas,
-                                         pgoff_t end_pgoff)
+/*
+ * Map page range [start_page, start_page + nr_pages) of folio.
+ * start_page is gotten from start by folio_page(folio, start)
+ */
+static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
+                       struct folio *folio, unsigned long start,
+                       unsigned long addr, unsigned int nr_pages)
 {
-       return next_uptodate_page(xas_find(xas, end_pgoff),
-                                 mapping, xas, end_pgoff);
-}
+       vm_fault_t ret = 0;
+       struct vm_area_struct *vma = vmf->vma;
+       struct file *file = vma->vm_file;
+       struct page *page = folio_page(folio, start);
+       unsigned int mmap_miss = READ_ONCE(file->f_ra.mmap_miss);
+       unsigned int ref_count = 0, count = 0;
 
-static inline struct folio *next_map_page(struct address_space *mapping,
-                                        struct xa_state *xas,
-                                        pgoff_t end_pgoff)
-{
-       return next_uptodate_page(xas_next_entry(xas, end_pgoff),
-                                 mapping, xas, end_pgoff);
+       do {
+               if (PageHWPoison(page))
+                       continue;
+
+               if (mmap_miss > 0)
+                       mmap_miss--;
+
+               /*
+                * NOTE: If there're PTE markers, we'll leave them to be
+                * handled in the specific fault path, and it'll prohibit the
+                * fault-around logic.
+                */
+               if (!pte_none(*vmf->pte))
+                       continue;
+
+               if (vmf->address == addr)
+                       ret = VM_FAULT_NOPAGE;
+
+               ref_count++;
+               do_set_pte(vmf, page, addr);
+               update_mmu_cache(vma, addr, vmf->pte);
+       } while (vmf->pte++, page++, addr += PAGE_SIZE, ++count < nr_pages);
+
+       /* Restore the vmf->pte */
+       vmf->pte -= nr_pages;
+
+       folio_ref_add(folio, ref_count);
+       WRITE_ONCE(file->f_ra.mmap_miss, mmap_miss);
+
+       return ret;
 }
 
 vm_fault_t filemap_map_pages(struct vm_fault *vmf,
@@ -3503,12 +3524,11 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf,
        unsigned long addr;
        XA_STATE(xas, &mapping->i_pages, start_pgoff);
        struct folio *folio;
-       struct page *page;
-       unsigned int mmap_miss = READ_ONCE(file->f_ra.mmap_miss);
        vm_fault_t ret = 0;
+       int nr_pages = 0;
 
        rcu_read_lock();
-       folio = first_map_page(mapping, &xas, end_pgoff);
+       folio = next_uptodate_folio(&xas, mapping, end_pgoff);
        if (!folio)
                goto out;
 
@@ -3525,17 +3545,13 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf,
                goto out;
        }
        do {
-again:
-               page = folio_file_page(folio, xas.xa_index);
-               if (PageHWPoison(page))
-                       goto unlock;
-
-               if (mmap_miss > 0)
-                       mmap_miss--;
+               unsigned long end;
 
                addr += (xas.xa_index - last_pgoff) << PAGE_SHIFT;
                vmf->pte += xas.xa_index - last_pgoff;
                last_pgoff = xas.xa_index;
+               end = folio->index + folio_nr_pages(folio) - 1;
+               nr_pages = min(end, end_pgoff) - xas.xa_index + 1;
 
                /*
                 * NOTE: If there're PTE markers, we'll leave them to be
@@ -3545,32 +3561,17 @@ again:
                if (!pte_none(ptep_get(vmf->pte)))
                        goto unlock;
 
-               /* We're about to handle the fault */
-               if (vmf->address == addr)
-                       ret = VM_FAULT_NOPAGE;
+               ret |= filemap_map_folio_range(vmf, folio,
+                               xas.xa_index - folio->index, addr, nr_pages);
 
-               do_set_pte(vmf, page, addr);
-               /* no need to invalidate: a not-present page won't be cached */
-               update_mmu_cache(vma, addr, vmf->pte);
-               if (folio_more_pages(folio, xas.xa_index, end_pgoff)) {
-                       xas.xa_index++;
-                       folio_ref_inc(folio);
-                       goto again;
-               }
-               folio_unlock(folio);
-               continue;
 unlock:
-               if (folio_more_pages(folio, xas.xa_index, end_pgoff)) {
-                       xas.xa_index++;
-                       goto again;
-               }
                folio_unlock(folio);
                folio_put(folio);
-       } while ((folio = next_map_page(mapping, &xas, end_pgoff)) != NULL);
+               folio = next_uptodate_folio(&xas, mapping, end_pgoff);
+       } while (folio);
        pte_unmap_unlock(vmf->pte, vmf->ptl);
 out:
        rcu_read_unlock();
-       WRITE_ONCE(file->f_ra.mmap_miss, mmap_miss);
        return ret;
 }
 EXPORT_SYMBOL(filemap_map_pages);