mm: put readahead pages in cache earlier

When populating the page cache for readahead, mappings that use
->readpages must populate the page cache themselves as the pages are
passed on a linked list which would normally be used for the page
cache's LRU.  For mappings that use ->readpage or the upcoming
->readahead method, we can put the pages into the page cache as soon as
they're allocated, which solves a race between readahead and direct IO.
It also lets us remove the gfp argument from read_pages().

Use the new readahead_page() API to implement the repeated calls to
->readpage(), just like most filesystems will.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Cc: Chao Yu <yuchao0@huawei.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Darrick J. Wong <darrick.wong@oracle.com>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Gao Xiang <gaoxiang25@huawei.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Link: http://lkml.kernel.org/r/20200414150233.24495-11-willy@infradead.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/readahead.c b/mm/readahead.c
index ddc63d3b07b8ddaa1ad48a71c67061eabacf9122..e52b3a7b9da58ca3f8c13134f978c1575b31edb6 100644 (file)
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -114,14 +114,14 @@ 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)
+               bool skip_page)
 {
        const struct address_space_operations *aops = rac->mapping->a_ops;
+       struct page *page;
        struct blk_plug plug;
-       unsigned page_idx;
 
        if (!readahead_count(rac))
-               return;
+               goto out;
 
        blk_start_plug(&plug);
 
@@ -130,23 +130,23 @@ 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))
+               rac->_index += rac->_nr_pages;
+               rac->_nr_pages = 0;
+       } else {
+               while ((page = readahead_page(rac))) {
                        aops->readpage(rac->file, page);
-               put_page(page);
+                       put_page(page);
+               }
        }
 
-out:
        blk_finish_plug(&plug);
 
        BUG_ON(!list_empty(pages));
-       rac->_nr_pages = 0;
+       BUG_ON(readahead_count(rac));
+
+out:
+       if (skip_page)
+               rac->_index++;
 }
 
 /*
@@ -168,6 +168,7 @@ void __do_page_cache_readahead(struct address_space *mapping,
        struct readahead_control rac = {
                .mapping = mapping,
                .file = filp,
+               ._index = index,
        };
        unsigned long i;
 
@@ -183,6 +184,8 @@ void __do_page_cache_readahead(struct address_space *mapping,
                if (index + i > end_index)
                        break;
 
+               BUG_ON(index + i != rac._index + rac._nr_pages);
+
                page = xa_load(&mapping->i_pages, index + i);
                if (page && !xa_is_value(page)) {
                        /*
@@ -190,15 +193,22 @@ void __do_page_cache_readahead(struct address_space *mapping,
                         * contiguous pages before continuing with the next
                         * batch.
                         */
-                       read_pages(&rac, &page_pool, gfp_mask);
+                       read_pages(&rac, &page_pool, true);
                        continue;
                }
 
                page = __page_cache_alloc(gfp_mask);
                if (!page)
                        break;
-               page->index = index + i;
-               list_add(&page->lru, &page_pool);
+               if (mapping->a_ops->readpages) {
+                       page->index = index + i;
+                       list_add(&page->lru, &page_pool);
+               } else if (add_to_page_cache_lru(page, mapping, index + i,
+                                       gfp_mask) < 0) {
+                       put_page(page);
+                       read_pages(&rac, &page_pool, true);
+                       continue;
+               }
                if (i == nr_to_read - lookahead_size)
                        SetPageReadahead(page);
                rac._nr_pages++;
@@ -209,7 +219,7 @@ void __do_page_cache_readahead(struct address_space *mapping,
         * uptodate then the caller will launch readpage again, and
         * will then handle the error.
         */
-       read_pages(&rac, &page_pool, gfp_mask);
+       read_pages(&rac, &page_pool, false);
 }
 
 /*