[PATCH 62/62] mm: Convert page-writeback to XArray

Matthew Wilcox
2017-11-22T21:08:50Z

Includes moving mapping_tagged() to fs.h as a static inline, and
changing it to return bool.

Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
---
include/linux/fs.h | 17 +++++++++------
mm/page-writeback.c | 63 +++++++++++++++++++----------------------------------
2 files changed, 33 insertions(+), 47 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index a5c105d292a7..14b7406e03e0 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -470,15 +470,18 @@ struct block_device {
struct mutex bd_fsfreeze_mutex;
} __randomize_layout;

+/* XArray tags, for tagging dirty and writeback pages in the pagecache. */
+#define PAGECACHE_TAG_DIRTY XA_TAG_0
+#define PAGECACHE_TAG_WRITEBACK XA_TAG_1
+#define PAGECACHE_TAG_TOWRITE XA_TAG_2
+
/*
- * Radix-tree tags, for tagging dirty and writeback pages within the pagecache
- * radix trees
+ * Returns true if any of the pages in the mapping are marked with the tag.
*/
-#define PAGECACHE_TAG_DIRTY 0
-#define PAGECACHE_TAG_WRITEBACK 1
-#define PAGECACHE_TAG_TOWRITE 2
-
-int mapping_tagged(struct address_space *mapping, int tag);
+static inline bool mapping_tagged(struct address_space *mapping, xa_tag_t tag)
+{
+ return xa_tagged(&mapping->pages, tag);
+}

static inline void i_mmap_lock_write(struct address_space *mapping)
{
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 6a5b92629727..28175cba7e72 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2100,33 +2100,26 @@ void __init page_writeback_init(void)
* dirty pages in the file (thus it is important for this function to be quick
* so that it can tag pages faster than a dirtying process can create them).
*/
-/*
- * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce xa_lock latency.
- */
void tag_pages_for_writeback(struct address_space *mapping,
pgoff_t start, pgoff_t end)
{
-#define WRITEBACK_TAG_BATCH 4096
- unsigned long tagged = 0;
- struct radix_tree_iter iter;
- void **slot;
+ XA_STATE(xas, start);
+ struct xarray *xa = &mapping->pages;
+ unsigned int tagged = 0;
+ void *page;

- xa_lock_irq(&mapping->pages);
- radix_tree_for_each_tagged(slot, &mapping->pages, &iter, start,
- PAGECACHE_TAG_DIRTY) {
- if (iter.index > end)
- break;
- radix_tree_iter_tag_set(&mapping->pages, &iter,
- PAGECACHE_TAG_TOWRITE);
- tagged++;
- if ((tagged % WRITEBACK_TAG_BATCH) != 0)
+ xa_lock_irq(xa);
+ xas_for_each_tag(xa, &xas, page, end, PAGECACHE_TAG_DIRTY) {
+ xas_set_tag(xa, &xas, PAGECACHE_TAG_TOWRITE);
+ if (++tagged % XA_CHECK_SCHED)
continue;
- slot = radix_tree_iter_resume(slot, &iter);
- xa_unlock_irq(&mapping->pages);
+
+ xas_pause(&xas);
+ xa_unlock_irq(xa);
cond_resched();
- xa_lock_irq(&mapping->pages);
+ xa_lock_irq(xa);
}
- xa_unlock_irq(&mapping->pages);
+ xa_unlock_irq(xa);
}
EXPORT_SYMBOL(tag_pages_for_writeback);

@@ -2166,7 +2159,7 @@ int write_cache_pages(struct address_space *mapping,
pgoff_t done_index;
int cycled;
int range_whole = 0;
- int tag;
+ xa_tag_t tag;

pagevec_init(&pvec);
if (wbc->range_cyclic) {
@@ -2447,7 +2440,7 @@ void account_page_cleaned(struct page *page, struct address_space *mapping,

/*
* For address_spaces which do not use buffers. Just tag the page as dirty in
- * its radix tree.
+ * the xarray.
*
* This is also used when a single buffer is being dirtied: we want to set the
* page dirty in that case, but not all the buffers. This is a "bottom-up"
@@ -2473,7 +2466,7 @@ int __set_page_dirty_nobuffers(struct page *page)
BUG_ON(page_mapping(page) != mapping);
WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
account_page_dirtied(page, mapping);
- radix_tree_tag_set(&mapping->pages, page_index(page),
+ __xa_set_tag(&mapping->pages, page_index(page),
PAGECACHE_TAG_DIRTY);
xa_unlock_irqrestore(&mapping->pages, flags);
unlock_page_memcg(page);
@@ -2636,13 +2629,13 @@ EXPORT_SYMBOL(__cancel_dirty_page);
* Returns true if the page was previously dirty.
*
* This is for preparing to put the page under writeout. We leave the page
- * tagged as dirty in the radix tree so that a concurrent write-for-sync
+ * tagged as dirty in the xarray so that a concurrent write-for-sync
* can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage
* implementation will run either set_page_writeback() or set_page_dirty(),
- * at which stage we bring the page's dirty flag and radix-tree dirty tag
+ * at which stage we bring the page's dirty flag and xarray dirty tag
* back into sync.
*
- * This incoherency between the page's dirty flag and radix-tree tag is
+ * This incoherency between the page's dirty flag and xarray tag is
* unfortunate, but it only exists while the page is locked.
*/
int clear_page_dirty_for_io(struct page *page)
@@ -2723,7 +2716,7 @@ int test_clear_page_writeback(struct page *page)
xa_lock_irqsave(&mapping->pages, flags);
ret = TestClearPageWriteback(page);
if (ret) {
- radix_tree_tag_clear(&mapping->pages, page_index(page),
+ __xa_clear_tag(&mapping->pages, page_index(page),
PAGECACHE_TAG_WRITEBACK);
if (bdi_cap_account_writeback(bdi)) {
struct bdi_writeback *wb = inode_to_wb(inode);
@@ -2775,7 +2768,7 @@ int __test_set_page_writeback(struct page *page, bool keep_write)
on_wblist = mapping_tagged(mapping,
PAGECACHE_TAG_WRITEBACK);

- radix_tree_tag_set(&mapping->pages, page_index(page),
+ __xa_set_tag(&mapping->pages, page_index(page),
PAGECACHE_TAG_WRITEBACK);
if (bdi_cap_account_writeback(bdi))
inc_wb_stat(inode_to_wb(inode), WB_WRITEBACK);
@@ -2789,10 +2782,10 @@ int __test_set_page_writeback(struct page *page, bool keep_write)
sb_mark_inode_writeback(mapping->host);
}
if (!PageDirty(page))
- radix_tree_tag_clear(&mapping->pages, page_index(page),
+ __xa_clear_tag(&mapping->pages, page_index(page),
PAGECACHE_TAG_DIRTY);
if (!keep_write)
- radix_tree_tag_clear(&mapping->pages, page_index(page),
+ __xa_clear_tag(&mapping->pages, page_index(page),
PAGECACHE_TAG_TOWRITE);
xa_unlock_irqrestore(&mapping->pages, flags);
} else {
@@ -2808,16 +2801,6 @@ int __test_set_page_writeback(struct page *page, bool keep_write)
}
EXPORT_SYMBOL(__test_set_page_writeback);

-/*
- * Return true if any of the pages in the mapping are marked with the
- * passed tag.
- */
-int mapping_tagged(struct address_space *mapping, int tag)
-{
- return radix_tree_tagged(&mapping->pages, tag);
-}
-EXPORT_SYMBOL(mapping_tagged);
-
/**
* wait_for_stable_page() - wait for writeback to finish, if necessary.
* @page: The page to wait on.
--
2.15.0