[PATCH v6 07/19] mm: Put readahead pages in cache earlier

Matthew Wilcox
2020-02-17T18:47:37Z

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

At allocation time, put the pages in the cache unless we're using
->readpages. Add the readahead_for_each() iterator for the benefit of
the ->readpage fallback. This iterator supports huge pages, even though
none of the filesystems to be converted do yet.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
include/linux/pagemap.h | 24 ++++++++++++++++++++++++
mm/readahead.c | 34 +++++++++++++++++-----------------
2 files changed, 41 insertions(+), 17 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 982ecda2d4a2..3613154e79e4 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -639,8 +639,32 @@ struct readahead_control {
/* private: use the readahead_* accessors instead */
pgoff_t _start;
unsigned int _nr_pages;
+ unsigned int _batch_count;
};

+static inline struct page *readahead_page(struct readahead_control *rac)
+{
+ struct page *page;
+
+ if (!rac->_nr_pages)
+ return NULL;
+
+ page = xa_load(&rac->mapping->i_pages, rac->_start);
+ VM_BUG_ON_PAGE(!PageLocked(page), page);
+ rac->_batch_count = hpage_nr_pages(page);
+
+ return page;
+}
+
+static inline void readahead_next(struct readahead_control *rac)
+{
+ rac->_nr_pages -= rac->_batch_count;
+ rac->_start += rac->_batch_count;
+}
+
+#define readahead_for_each(rac, page) \
+ for (; (page = readahead_page(rac)); readahead_next(rac))
+
/* The number of pages in this readahead block */
static inline unsigned int readahead_count(struct readahead_control *rac)
{
diff --git a/mm/readahead.c b/mm/readahead.c
index bdc5759000d3..9e430daae42f 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -113,12 +113,11 @@ int read_cache_pages(struct address_space *mapping, struct list_head *pages,

EXPORT_SYMBOL(read_cache_pages);

-static void read_pages(struct readahead_control *rac, struct list_head *pages,
- gfp_t gfp)
+static void read_pages(struct readahead_control *rac, struct list_head *pages)
{
const struct address_space_operations *aops = rac->mapping->a_ops;
+ struct page *page;
struct blk_plug plug;
- unsigned page_idx;

blk_start_plug(&plug);

@@ -127,19 +126,13 @@ static void read_pages(struct readahead_control *rac, struct list_head *pages,
readahead_count(rac));
/* Clean up the remaining pages */
put_pages_list(pages);
- goto out;
- }
-
- for (page_idx = 0; page_idx < readahead_count(rac); page_idx++) {
- struct page *page = lru_to_page(pages);
- list_del(&page->lru);
- if (!add_to_page_cache_lru(page, rac->mapping, page->index,
- gfp))
+ } else {
+ readahead_for_each(rac, page) {
aops->readpage(rac->file, page);
- put_page(page);
+ put_page(page);
+ }
}

-out:
blk_finish_plug(&plug);
}

@@ -159,6 +152,7 @@ void __do_page_cache_readahead(struct address_space *mapping,
unsigned long i;
loff_t isize = i_size_read(inode);
gfp_t gfp_mask = readahead_gfp_mask(mapping);
+ bool use_list = mapping->a_ops->readpages;
struct readahead_control rac = {
.mapping = mapping,
.file = filp,
@@ -196,8 +190,14 @@ void __do_page_cache_readahead(struct address_space *mapping,
page = __page_cache_alloc(gfp_mask);
if (!page)
break;
- page->index = offset;
- list_add(&page->lru, &page_pool);
+ if (use_list) {
+ page->index = offset;
+ list_add(&page->lru, &page_pool);
+ } else if (add_to_page_cache_lru(page, mapping, offset,
+ gfp_mask) < 0) {
+ put_page(page);
+ goto read;
+ }
if (i == nr_to_read - lookahead_size)
SetPageReadahead(page);
rac._nr_pages++;
@@ -205,7 +205,7 @@ void __do_page_cache_readahead(struct address_space *mapping,
continue;
read:
if (readahead_count(&rac))
- read_pages(&rac, &page_pool, gfp_mask);
+ read_pages(&rac, &page_pool);
rac._nr_pages = 0;
rac._start = ++offset;
}
@@ -216,7 +216,7 @@ void __do_page_cache_readahead(struct address_space *mapping,
* will then handle the error.
*/
if (readahead_count(&rac))
- read_pages(&rac, &page_pool, gfp_mask);
+ read_pages(&rac, &page_pool);
BUG_ON(!list_empty(&page_pool));
}

--
2.25.0