mm: page cache: store only head pages in i_pages

Transparent Huge Pages are currently stored in i_pages as pointers to
consecutive subpages.  This patch changes that to storing consecutive
pointers to the head page in preparation for storing huge pages more
efficiently in i_pages.

Large parts of this are "inspired" by Kirill's patch
https://lore.kernel.org/lkml/20170126115819.58875-2-kirill.shutemov@linux.intel.com/

Kirill and Huang Ying contributed several fixes.

[willy@infradead.org: use compound_nr, squish uninit-var warning]
Link: http://lkml.kernel.org/r/20190731210400.7419-1-willy@infradead.org
Signed-off-by: Matthew Wilcox <willy@infradead.org>
Acked-by: Jan Kara <jack@suse.cz>
Reviewed-by: Kirill Shutemov <kirill@shutemov.name>
Reviewed-by: Song Liu <songliubraving@fb.com>
Tested-by: Song Liu <songliubraving@fb.com>
Tested-by: William Kucharski <william.kucharski@oracle.com>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Tested-by: Qian Cai <cai@lca.pw>
Tested-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Song Liu <songliubraving@fb.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index c755245..37a4d9e 100644 (file)
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -333,6 +333,16 @@ static inline struct page *grab_cache_page_nowait(struct address_space *mapping,
                        mapping_gfp_mask(mapping));
 }
 
+static inline struct page *find_subpage(struct page *page, pgoff_t offset)
+{
+       if (PageHuge(page))
+               return page;
+
+       VM_BUG_ON_PAGE(PageTail(page), page);
+
+       return page + (offset & (compound_nr(page) - 1));
+}
+
 struct page *find_get_entry(struct address_space *mapping, pgoff_t offset);
 struct page *find_lock_entry(struct address_space *mapping, pgoff_t offset);
 unsigned find_get_entries(struct address_space *mapping, pgoff_t start,

diff --git a/mm/filemap.c b/mm/filemap.c
index d5462d7..533f271 100644 (file)
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -281,11 +281,11 @@ EXPORT_SYMBOL(delete_from_page_cache);
  * @pvec: pagevec with pages to delete
  *
  * The function walks over mapping->i_pages and removes pages passed in @pvec
- * from the mapping. The function expects @pvec to be sorted by page index.
+ * 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 and takes care to delete all corresponding tail pages from the
- * mapping as well.
+ * @pvec.
  *
  * The function expects the i_pages lock to be held.
  */
@@ -294,40 +294,43 @@ static void page_cache_delete_batch(struct address_space *mapping,
 {
        XA_STATE(xas, &mapping->i_pages, pvec->pages[0]->index);
        int total_pages = 0;
-       int i = 0, tail_pages = 0;
+       int i = 0;
        struct page *page;
 
        mapping_set_update(&xas, mapping);
        xas_for_each(&xas, page, ULONG_MAX) {
-               if (i >= pagevec_count(pvec) && !tail_pages)
+               if (i >= pagevec_count(pvec))
                        break;
+
+               /* A swap/dax/shadow entry got inserted? Skip it. */
                if (xa_is_value(page))
                        continue;
-               if (!tail_pages) {
-                       /*
-                        * Some page got inserted in our range? Skip it. We
-                        * have our pages locked so they are protected from
-                        * being removed.
-                        */
-                       if (page != pvec->pages[i]) {
-                               VM_BUG_ON_PAGE(page->index >
-                                               pvec->pages[i]->index, page);
-                               continue;
-                       }
-                       WARN_ON_ONCE(!PageLocked(page));
-                       if (PageTransHuge(page) && !PageHuge(page))
-                               tail_pages = HPAGE_PMD_NR - 1;
+               /*
+                * A page got inserted in our range? Skip it. We have our
+                * pages locked so they are protected from being removed.
+                * If we see a page whose index is higher than ours, it
+                * means our page has been removed, which shouldn't be
+                * possible because we're holding the PageLock.
+                */
+               if (page != pvec->pages[i]) {
+                       VM_BUG_ON_PAGE(page->index > pvec->pages[i]->index,
+                                       page);
+                       continue;
+               }
+
+               WARN_ON_ONCE(!PageLocked(page));
+
+               if (page->index == xas.xa_index)
                        page->mapping = NULL;
-                       /*
-                        * Leave page->index set: truncation lookup relies
-                        * upon it
-                        */
+               /* Leave page->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 (page->index + compound_nr(page) - 1 == xas.xa_index)
                        i++;
-               } else {
-                       VM_BUG_ON_PAGE(page->index + HPAGE_PMD_NR - tail_pages
-                                       != pvec->pages[i]->index, page);
-                       tail_pages--;
-               }
                xas_store(&xas, NULL);
                total_pages++;
        }
@@ -1520,7 +1523,7 @@ EXPORT_SYMBOL(page_cache_prev_miss);
 struct page *find_get_entry(struct address_space *mapping, pgoff_t offset)
 {
        XA_STATE(xas, &mapping->i_pages, offset);
-       struct page *head, *page;
+       struct page *page;
 
        rcu_read_lock();
 repeat:
@@ -1535,25 +1538,19 @@ repeat:
        if (!page || xa_is_value(page))
                goto out;
 
-       head = compound_head(page);
-       if (!page_cache_get_speculative(head))
-               goto repeat;
-
-       /* The page was split under us? */
-       if (compound_head(page) != head) {
-               put_page(head);
+       if (!page_cache_get_speculative(page))
                goto repeat;
-       }
 
        /*
-        * Has the page moved?
+        * Has the page moved or been split?
         * This is part of the lockless pagecache protocol. See
         * include/linux/pagemap.h for details.
         */
        if (unlikely(page != xas_reload(&xas))) {
-               put_page(head);
+               put_page(page);
                goto repeat;
        }
+       page = find_subpage(page, offset);
 out:
        rcu_read_unlock();
 
@@ -1735,7 +1732,6 @@ unsigned find_get_entries(struct address_space *mapping,
 
        rcu_read_lock();
        xas_for_each(&xas, page, ULONG_MAX) {
-               struct page *head;
                if (xas_retry(&xas, page))
                        continue;
                /*
@@ -1746,17 +1742,13 @@ unsigned find_get_entries(struct address_space *mapping,
                if (xa_is_value(page))
                        goto export;
 
-               head = compound_head(page);
-               if (!page_cache_get_speculative(head))
+               if (!page_cache_get_speculative(page))
                        goto retry;
 
-               /* The page was split under us? */
-               if (compound_head(page) != head)
-                       goto put_page;
-
-               /* Has the page moved? */
+               /* Has the page moved or been split? */
                if (unlikely(page != xas_reload(&xas)))
                        goto put_page;
+               page = find_subpage(page, xas.xa_index);
 
 export:
                indices[ret] = xas.xa_index;
@@ -1765,7 +1757,7 @@ export:
                        break;
                continue;
 put_page:
-               put_page(head);
+               put_page(page);
 retry:
                xas_reset(&xas);
        }
@@ -1807,33 +1799,27 @@ unsigned find_get_pages_range(struct address_space *mapping, pgoff_t *start,
 
        rcu_read_lock();
        xas_for_each(&xas, page, end) {
-               struct page *head;
                if (xas_retry(&xas, page))
                        continue;
                /* Skip over shadow, swap and DAX entries */
                if (xa_is_value(page))
                        continue;
 
-               head = compound_head(page);
-               if (!page_cache_get_speculative(head))
+               if (!page_cache_get_speculative(page))
                        goto retry;
 
-               /* The page was split under us? */
-               if (compound_head(page) != head)
-                       goto put_page;
-
-               /* Has the page moved? */
+               /* Has the page moved or been split? */
                if (unlikely(page != xas_reload(&xas)))
                        goto put_page;
 
-               pages[ret] = page;
+               pages[ret] = find_subpage(page, xas.xa_index);
                if (++ret == nr_pages) {
                        *start = xas.xa_index + 1;
                        goto out;
                }
                continue;
 put_page:
-               put_page(head);
+               put_page(page);
 retry:
                xas_reset(&xas);
        }
@@ -1878,7 +1864,6 @@ unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t index,
 
        rcu_read_lock();
        for (page = xas_load(&xas); page; page = xas_next(&xas)) {
-               struct page *head;
                if (xas_retry(&xas, page))
                        continue;
                /*
@@ -1888,24 +1873,19 @@ unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t index,
                if (xa_is_value(page))
                        break;
 
-               head = compound_head(page);
-               if (!page_cache_get_speculative(head))
+               if (!page_cache_get_speculative(page))
                        goto retry;
 
-               /* The page was split under us? */
-               if (compound_head(page) != head)
-                       goto put_page;
-
-               /* Has the page moved? */
+               /* Has the page moved or been split? */
                if (unlikely(page != xas_reload(&xas)))
                        goto put_page;
 
-               pages[ret] = page;
+               pages[ret] = find_subpage(page, xas.xa_index);
                if (++ret == nr_pages)
                        break;
                continue;
 put_page:
-               put_page(head);
+               put_page(page);
 retry:
                xas_reset(&xas);
        }
@@ -1941,7 +1921,6 @@ unsigned find_get_pages_range_tag(struct address_space *mapping, pgoff_t *index,
 
        rcu_read_lock();
        xas_for_each_marked(&xas, page, end, tag) {
-               struct page *head;
                if (xas_retry(&xas, page))
                        continue;
                /*
@@ -1952,26 +1931,21 @@ unsigned find_get_pages_range_tag(struct address_space *mapping, pgoff_t *index,
                if (xa_is_value(page))
                        continue;
 
-               head = compound_head(page);
-               if (!page_cache_get_speculative(head))
+               if (!page_cache_get_speculative(page))
                        goto retry;
 
-               /* The page was split under us? */
-               if (compound_head(page) != head)
-                       goto put_page;
-
-               /* Has the page moved? */
+               /* Has the page moved or been split? */
                if (unlikely(page != xas_reload(&xas)))
                        goto put_page;
 
-               pages[ret] = page;
+               pages[ret] = find_subpage(page, xas.xa_index);
                if (++ret == nr_pages) {
                        *index = xas.xa_index + 1;
                        goto out;
                }
                continue;
 put_page:
-               put_page(head);
+               put_page(page);
 retry:
                xas_reset(&xas);
        }
@@ -2652,7 +2626,7 @@ void filemap_map_pages(struct vm_fault *vmf,
        pgoff_t last_pgoff = start_pgoff;
        unsigned long max_idx;
        XA_STATE(xas, &mapping->i_pages, start_pgoff);
-       struct page *head, *page;
+       struct page *page;
 
        rcu_read_lock();
        xas_for_each(&xas, page, end_pgoff) {
@@ -2661,24 +2635,19 @@ void filemap_map_pages(struct vm_fault *vmf,
                if (xa_is_value(page))
                        goto next;
 
-               head = compound_head(page);
-
                /*
                 * Check for a locked page first, as a speculative
                 * reference may adversely influence page migration.
                 */
-               if (PageLocked(head))
+               if (PageLocked(page))
                        goto next;
-               if (!page_cache_get_speculative(head))
+               if (!page_cache_get_speculative(page))
                        goto next;
 
-               /* The page was split under us? */
-               if (compound_head(page) != head)
-                       goto skip;
-
-               /* Has the page moved? */
+               /* Has the page moved or been split? */
                if (unlikely(page != xas_reload(&xas)))
                        goto skip;
+               page = find_subpage(page, xas.xa_index);
 
                if (!PageUptodate(page) ||
                                PageReadahead(page) ||

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index de1f159..483b07b 100644 (file)
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2497,6 +2497,8 @@ static void __split_huge_page(struct page *page, struct list_head *list,
        struct page *head = compound_head(page);
        pg_data_t *pgdat = page_pgdat(head);
        struct lruvec *lruvec;
+       struct address_space *swap_cache = NULL;
+       unsigned long offset = 0;
        int i;
 
        lruvec = mem_cgroup_page_lruvec(head, pgdat);
@@ -2504,6 +2506,14 @@ static void __split_huge_page(struct page *page, struct list_head *list,
        /* complete memcg works before add pages to LRU */
        mem_cgroup_split_huge_fixup(head);
 
+       if (PageAnon(head) && PageSwapCache(head)) {
+               swp_entry_t entry = { .val = page_private(head) };
+
+               offset = swp_offset(entry);
+               swap_cache = swap_address_space(entry);
+               xa_lock(&swap_cache->i_pages);
+       }
+
        for (i = HPAGE_PMD_NR - 1; i >= 1; i--) {
                __split_huge_page_tail(head, i, lruvec, list);
                /* Some pages can be beyond i_size: drop them from page cache */
@@ -2513,6 +2523,12 @@ static void __split_huge_page(struct page *page, struct list_head *list,
                        if (IS_ENABLED(CONFIG_SHMEM) && PageSwapBacked(head))
                                shmem_uncharge(head->mapping->host, 1);
                        put_page(head + i);
+               } else if (!PageAnon(page)) {
+                       __xa_store(&head->mapping->i_pages, head[i].index,
+                                       head + i, 0);
+               } else if (swap_cache) {
+                       __xa_store(&swap_cache->i_pages, offset + i,
+                                       head + i, 0);
                }
        }
 
@@ -2523,10 +2539,12 @@ static void __split_huge_page(struct page *page, struct list_head *list,
        /* See comment in __split_huge_page_tail() */
        if (PageAnon(head)) {
                /* Additional pin to swap cache */
-               if (PageSwapCache(head))
+               if (PageSwapCache(head)) {
                        page_ref_add(head, 2);
-               else
+                       xa_unlock(&swap_cache->i_pages);
+               } else {
                        page_ref_inc(head);
+               }
        } else {
                /* Additional pin to page cache */
                page_ref_add(head, 2);

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index ccede24..04a54ff 100644 (file)
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1378,7 +1378,7 @@ static void collapse_shmem(struct mm_struct *mm,
                                result = SCAN_FAIL;
                                goto xa_locked;
                        }
-                       xas_store(&xas, new_page + (index % HPAGE_PMD_NR));
+                       xas_store(&xas, new_page);
                        nr_none++;
                        continue;
                }
@@ -1454,7 +1454,7 @@ static void collapse_shmem(struct mm_struct *mm,
                list_add_tail(&page->lru, &pagelist);
 
                /* Finally, replace with the new page. */
-               xas_store(&xas, new_page + (index % HPAGE_PMD_NR));
+               xas_store(&xas, new_page);
                continue;
 out_unlock:
                unlock_page(page);

diff --git a/mm/memfd.c b/mm/memfd.c
index 650e65a..2647c89 100644 (file)
--- a/mm/memfd.c
+++ b/mm/memfd.c
@@ -39,6 +39,7 @@ static void memfd_tag_pins(struct xa_state *xas)
        xas_for_each(xas, page, ULONG_MAX) {
                if (xa_is_value(page))
                        continue;
+               page = find_subpage(page, xas->xa_index);
                if (page_count(page) - page_mapcount(page) > 1)
                        xas_set_mark(xas, MEMFD_TAG_PINNED);
 
@@ -88,6 +89,7 @@ static int memfd_wait_for_pins(struct address_space *mapping)
                        bool clear = true;
                        if (xa_is_value(page))
                                continue;
+                       page = find_subpage(page, xas.xa_index);
                        if (page_count(page) - page_mapcount(page) != 1) {
                                /*
                                 * On the last scan, we clean up all those tags

diff --git a/mm/migrate.c b/mm/migrate.c
index aa72b49..374ef2f 100644 (file)
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -460,7 +460,7 @@ int migrate_page_move_mapping(struct address_space *mapping,
 
                for (i = 1; i < HPAGE_PMD_NR; i++) {
                        xas_next(&xas);
-                       xas_store(&xas, newpage + i);
+                       xas_store(&xas, newpage);
                }
        }
 

diff --git a/mm/shmem.c b/mm/shmem.c
index 15d26c8..57a6aed 100644 (file)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -631,7 +631,7 @@ static int shmem_add_to_page_cache(struct page *page,
                if (xas_error(&xas))
                        goto unlock;
 next:
-               xas_store(&xas, page + i);
+               xas_store(&xas, page);
                if (++i < nr) {
                        xas_next(&xas);
                        goto next;

diff --git a/mm/swap_state.c b/mm/swap_state.c
index f844af5..8e7ce9a 100644 (file)
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -133,7 +133,7 @@ int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp)
                for (i = 0; i < nr; i++) {
                        VM_BUG_ON_PAGE(xas.xa_index != idx + i, page);
                        set_page_private(page + i, entry.val + i);
-                       xas_store(&xas, page + i);
+                       xas_store(&xas, page);
                        xas_next(&xas);
                }
                address_space->nrpages += nr;
@@ -168,7 +168,7 @@ void __delete_from_swap_cache(struct page *page, swp_entry_t entry)
 
        for (i = 0; i < nr; i++) {
                void *entry = xas_store(&xas, NULL);
-               VM_BUG_ON_PAGE(entry != page + i, entry);
+               VM_BUG_ON_PAGE(entry != page, entry);
                set_page_private(page + i, 0);
                xas_next(&xas);
        }