@@ -1078,16 +1078,6 @@ static inline unsigned int __readahead_batch(struct readahead_control *rac,
VM_BUG_ON_PAGE(PageTail(page), page);
array[i++] = page;
rac->_batch_count += thp_nr_pages(page);
-
- /*
- * The page cache isn't using multi-index entries yet,
- * so the xas cursor needs to be manually moved to the
- * next index. This can be removed once the page cache
- * is converted.
- */
- if (PageHead(page))
- xas_set(&xas, rac->_index + rac->_batch_count);
-
if (i == array_sz)
break;
}
@@ -134,7 +134,6 @@ static void page_cache_delete(struct address_space *mapping,
}
VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
- VM_BUG_ON_FOLIO(nr != 1 && shadow, folio);
xas_store(&xas, shadow);
xas_init_marks(&xas);
@@ -276,8 +275,7 @@ void filemap_remove_folio(struct folio *folio)
* from the mapping. The function expects @pvec to be sorted by page index
* and is optimised for it to be dense.
* It tolerates holes in @pvec (mapping entries at those indices are not
- * modified). The function expects only THP head pages to be present in the
- * @pvec.
+ * modified). The function expects only folios to be present in the @pvec.
*
* The function expects the i_pages lock to be held.
*/
@@ -312,20 +310,12 @@ static void page_cache_delete_batch(struct address_space *mapping,
WARN_ON_ONCE(!folio_test_locked(folio));
- if (folio->index == xas.xa_index)
- folio->mapping = NULL;
- /* Leave page->index set: truncation lookup relies on it */
+ folio->mapping = NULL;
+ /* Leave folio->index set: truncation lookup relies on it */
- /*
- * Move to the next page in the vector if this is a regular
- * page or the index is of the last sub-page of this compound
- * page.
- */
- if (folio->index + folio_nr_pages(folio) - 1 ==
- xas.xa_index)
- i++;
+ i++;
xas_store(&xas, NULL);
- total_pages++;
+ total_pages += folio_nr_pages(folio);
}
mapping->nrpages -= total_pages;
}
@@ -2027,24 +2017,27 @@ unsigned find_lock_entries(struct address_space *mapping, pgoff_t start,
indices[pvec->nr] = xas.xa_index;
if (!pagevec_add(pvec, &folio->page))
break;
- goto next;
+ continue;
unlock:
folio_unlock(folio);
put:
folio_put(folio);
-next:
- if (!xa_is_value(folio) && folio_multi(folio)) {
- xas_set(&xas, folio->index + folio_nr_pages(folio));
- /* Did we wrap on 32-bit? */
- if (!xas.xa_index)
- break;
- }
}
rcu_read_unlock();
return pagevec_count(pvec);
}
+static inline
+bool folio_more_pages(struct folio *folio, pgoff_t index, pgoff_t max)
+{
+ if (folio_single(folio) || folio_test_hugetlb(folio))
+ return false;
+ if (index >= max)
+ return false;
+ return index < folio->index + folio_nr_pages(folio) - 1;
+}
+
/**
* find_get_pages_range - gang pagecache lookup
* @mapping: The address_space to search
@@ -2083,11 +2076,17 @@ unsigned find_get_pages_range(struct address_space *mapping, pgoff_t *start,
if (xa_is_value(folio))
continue;
+again:
pages[ret] = folio_file_page(folio, xas.xa_index);
if (++ret == nr_pages) {
*start = xas.xa_index + 1;
goto out;
}
+ if (folio_more_pages(folio, xas.xa_index, end)) {
+ xas.xa_index++;
+ folio_ref_inc(folio);
+ goto again;
+ }
}
/*
@@ -2145,9 +2144,15 @@ unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t index,
if (unlikely(folio != xas_reload(&xas)))
goto put_page;
- pages[ret] = &folio->page;
+again:
+ pages[ret] = folio_file_page(folio, xas.xa_index);
if (++ret == nr_pages)
break;
+ if (folio_more_pages(folio, xas.xa_index, ULONG_MAX)) {
+ xas.xa_index++;
+ folio_ref_inc(folio);
+ goto again;
+ }
continue;
put_page:
folio_put(folio);
@@ -3169,6 +3174,7 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf,
addr = vma->vm_start + ((start_pgoff - vma->vm_pgoff) << PAGE_SHIFT);
vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, addr, &vmf->ptl);
do {
+again:
page = folio_file_page(folio, xas.xa_index);
if (PageHWPoison(page))
goto unlock;
@@ -3190,9 +3196,18 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf,
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);
@@ -2638,6 +2638,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
{
struct page *head = compound_head(page);
struct deferred_split *ds_queue = get_deferred_split_queue(head);
+ XA_STATE(xas, &head->mapping->i_pages, head->index);
struct anon_vma *anon_vma = NULL;
struct address_space *mapping = NULL;
int extra_pins, ret;
@@ -2700,18 +2701,27 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
unmap_page(head);
+ if (mapping) {
+ xas_split_alloc(&xas, head, compound_order(head),
+ mapping_gfp_mask(mapping) & GFP_RECLAIM_MASK);
+ if (xas_error(&xas)) {
+ ret = xas_error(&xas);
+ goto out_unlock;
+ }
+ }
+
/* block interrupt reentry in xa_lock and spinlock */
local_irq_disable();
if (mapping) {
- XA_STATE(xas, &mapping->i_pages, page_index(head));
-
/*
* Check if the head page is present in page cache.
* We assume all tail are present too, if head is there.
*/
- xa_lock(&mapping->i_pages);
+ xas_lock(&xas);
+ xas_reset(&xas);
if (xas_load(&xas) != head)
goto fail;
+ xas_split(&xas, head, thp_order(head));
}
/* Prevent deferred_split_scan() touching ->_refcount */
@@ -2739,7 +2749,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
spin_unlock(&ds_queue->split_queue_lock);
fail:
if (mapping)
- xa_unlock(&mapping->i_pages);
+ xas_unlock(&xas);
local_irq_enable();
remap_page(head, thp_nr_pages(head));
ret = -EBUSY;
@@ -2753,6 +2763,8 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
if (mapping)
i_mmap_unlock_read(mapping);
out:
+ /* Free any memory we didn't use */
+ xas_nomem(&xas, 0);
count_vm_event(!ret ? THP_SPLIT_PAGE : THP_SPLIT_PAGE_FAILED);
return ret;
}
@@ -1664,7 +1664,10 @@ static void collapse_file(struct mm_struct *mm,
}
count_memcg_page_event(new_page, THP_COLLAPSE_ALLOC);
- /* This will be less messy when we use multi-index entries */
+ /*
+ * Ensure we have slots for all the pages in the range. This is
+ * almost certainly a no-op because most of the pages must be present
+ */
do {
xas_lock_irq(&xas);
xas_create_range(&xas);
@@ -1884,6 +1887,9 @@ static void collapse_file(struct mm_struct *mm,
__mod_lruvec_page_state(new_page, NR_SHMEM, nr_none);
}
+ /* Join all the small entries into a single multi-index entry */
+ xas_set_order(&xas, start, HPAGE_PMD_ORDER);
+ xas_store(&xas, new_page);
xa_locked:
xas_unlock_irq(&xas);
xa_unlocked:
@@ -2005,6 +2011,10 @@ static void khugepaged_scan_file(struct mm_struct *mm,
continue;
}
+ /*
+ * XXX: khugepaged should compact smaller compound pages
+ * into a PMD sized page
+ */
if (PageTransCompound(page)) {
result = SCAN_PAGE_COMPOUND;
break;
@@ -439,14 +439,6 @@ int folio_migrate_mapping(struct address_space *mapping,
}
xas_store(&xas, newfolio);
- if (nr > 1) {
- int i;
-
- for (i = 1; i < nr; i++) {
- xas_next(&xas);
- xas_store(&xas, newfolio);
- }
- }
/*
* Drop cache reference from old page by unfreezing
@@ -670,7 +670,6 @@ static int shmem_add_to_page_cache(struct page *page,
struct mm_struct *charge_mm)
{
XA_STATE_ORDER(xas, &mapping->i_pages, index, compound_order(page));
- unsigned long i = 0;
unsigned long nr = compound_nr(page);
int error;
@@ -700,17 +699,11 @@ static int shmem_add_to_page_cache(struct page *page,
void *entry;
xas_lock_irq(&xas);
entry = xas_find_conflict(&xas);
- if (entry != expected)
+ if (entry != expected) {
xas_set_err(&xas, -EEXIST);
- xas_create_range(&xas);
- if (xas_error(&xas))
goto unlock;
-next:
- xas_store(&xas, page);
- if (++i < nr) {
- xas_next(&xas);
- goto next;
}
+ xas_store(&xas, page);
if (PageTransHuge(page)) {
count_vm_event(THP_FILE_ALLOC);
__mod_lruvec_page_state(page, NR_SHMEM_THPS, nr);
We currently store order-N THPs as 2^N consecutive entries. While this consumes rather more memory than necessary, it also turns out to be buggy. A writeback operation which starts in the middle of a dirty THP will not notice as the dirty bit is only set on the head index. With multi-index entries, the dirty bit will be found no matter where in the THP the iteration starts. This does end up simplifying the page cache slightly, although not as much as I had hoped. Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> --- include/linux/pagemap.h | 10 ------- mm/filemap.c | 63 +++++++++++++++++++++++++---------------- mm/huge_memory.c | 20 ++++++++++--- mm/khugepaged.c | 12 +++++++- mm/migrate.c | 8 ------ mm/shmem.c | 11 ++----- 6 files changed, 68 insertions(+), 56 deletions(-)