add patch create-function-to-read-journal-inode

[ext4-patch-queue.git] / include-mpage-functions-into-readpage.c

ext4: copy mpage_readpage() and mpage_readpages() fs/ext4/readpage.c

Move the functions which we need from fs/mpage.c into
fs/ext4/readpage.c.  This will allow us to proceed with the
refactorization of these functions and eventual merger with the
functions in fs/ext4/page_io.c.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
---
 fs/ext4/readpage.c | 326 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 320 insertions(+), 6 deletions(-)

diff --git a/fs/ext4/readpage.c b/fs/ext4/readpage.c
index b5249db..3b29da1 100644
--- a/fs/ext4/readpage.c
+++ b/fs/ext4/readpage.c
@@ -23,6 +23,7 @@
 #include <linux/ratelimit.h>
 #include <linux/aio.h>
 #include <linux/bitops.h>
+#include <linux/cleancache.h>
 
 #include "ext4_jbd2.h"
 #include "xattr.h"
@@ -30,31 +31,344 @@
 
 #include <trace/events/ext4.h>
 
-int ext4_readpage(struct file *file, struct page *page)
+/*
+ * I/O completion handler for multipage BIOs.
+ *
+ * The mpage code never puts partial pages into a BIO (except for end-of-file).
+ * If a page does not map to a contiguous run of blocks then it simply falls
+ * back to block_read_full_page().
+ *
+ * Why is this?  If a page's completion depends on a number of different BIOs
+ * which can complete in any order (or at the same time) then determining the
+ * status of that page is hard.  See end_buffer_async_read() for the details.
+ * There is no point in duplicating all that complexity.
+ */
+static void mpage_end_io(struct bio *bio, int err)
+{
+       struct bio_vec *bv;
+       int i;
+
+       bio_for_each_segment_all(bv, bio, i) {
+               struct page *page = bv->bv_page;
+               page_endio(page, bio_data_dir(bio), err);
+       }
+
+       bio_put(bio);
+}
+
+static struct bio *mpage_bio_submit(int rw, struct bio *bio)
+{
+       bio->bi_end_io = mpage_end_io;
+       submit_bio(rw, bio);
+       return NULL;
+}
+
+static struct bio *
+mpage_alloc(struct block_device *bdev,
+               sector_t first_sector, int nr_vecs,
+               gfp_t gfp_flags)
+{
+       struct bio *bio;
+
+       bio = bio_alloc(gfp_flags, nr_vecs);
+
+       if (bio == NULL && (current->flags & PF_MEMALLOC)) {
+               while (!bio && (nr_vecs /= 2))
+                       bio = bio_alloc(gfp_flags, nr_vecs);
+       }
+
+       if (bio) {
+               bio->bi_bdev = bdev;
+               bio->bi_iter.bi_sector = first_sector;
+       }
+       return bio;
+}
+
+/*
+ * support function for mpage_readpages.  The fs supplied get_block might
+ * return an up to date buffer.  This is used to map that buffer into
+ * the page, which allows readpage to avoid triggering a duplicate call
+ * to get_block.
+ *
+ * The idea is to avoid adding buffers to pages that don't already have
+ * them.  So when the buffer is up to date and the page size == block size,
+ * this marks the page up to date instead of adding new buffers.
+ */
+static void
+map_buffer_to_page(struct page *page, struct buffer_head *bh, int page_block)
+{
+       struct inode *inode = page->mapping->host;
+       struct buffer_head *page_bh, *head;
+       int block = 0;
+
+       if (!page_has_buffers(page)) {
+               /*
+                * don't make any buffers if there is only one buffer on
+                * the page and the page just needs to be set up to date
+                */
+               if (inode->i_blkbits == PAGE_CACHE_SHIFT &&
+                   buffer_uptodate(bh)) {
+                       SetPageUptodate(page);
+                       return;
+               }
+               create_empty_buffers(page, 1 << inode->i_blkbits, 0);
+       }
+       head = page_buffers(page);
+       page_bh = head;
+       do {
+               if (block == page_block) {
+                       page_bh->b_state = bh->b_state;
+                       page_bh->b_bdev = bh->b_bdev;
+                       page_bh->b_blocknr = bh->b_blocknr;
+                       break;
+               }
+               page_bh = page_bh->b_this_page;
+               block++;
+       } while (page_bh != head);
+}
+
+/*
+ * This is the worker routine which does all the work of mapping the disk
+ * blocks and constructs largest possible bios, submits them for IO if the
+ * blocks are not contiguous on the disk.
+ *
+ * We pass a buffer_head back and forth and use its buffer_mapped() flag to
+ * represent the validity of its disk mapping and to decide when to do the next
+ * get_block() call.
+ */
+static struct bio *
+do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
+               sector_t *last_block_in_bio, struct buffer_head *map_bh,
+               unsigned long *first_logical_block, get_block_t get_block)
 {
-       int ret = -EAGAIN;
        struct inode *inode = page->mapping->host;
+       const unsigned blkbits = inode->i_blkbits;
+       const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
+       const unsigned blocksize = 1 << blkbits;
+       sector_t block_in_file;
+       sector_t last_block;
+       sector_t last_block_in_file;
+       sector_t blocks[MAX_BUF_PER_PAGE];
+       unsigned page_block;
+       unsigned first_hole = blocks_per_page;
+       struct block_device *bdev = NULL;
+       int length;
+       int fully_mapped = 1;
+       unsigned nblocks;
+       unsigned relative_block;
+
+       if (page_has_buffers(page))
+               goto confused;
+
+       block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
+       last_block = block_in_file + nr_pages * blocks_per_page;
+       last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
+       if (last_block > last_block_in_file)
+               last_block = last_block_in_file;
+       page_block = 0;
+
+       /*
+        * Map blocks using the result from the previous get_blocks call first.
+        */
+       nblocks = map_bh->b_size >> blkbits;
+       if (buffer_mapped(map_bh) && block_in_file > *first_logical_block &&
+                       block_in_file < (*first_logical_block + nblocks)) {
+               unsigned map_offset = block_in_file - *first_logical_block;
+               unsigned last = nblocks - map_offset;
+
+               for (relative_block = 0; ; relative_block++) {
+                       if (relative_block == last) {
+                               clear_buffer_mapped(map_bh);
+                               break;
+                       }
+                       if (page_block == blocks_per_page)
+                               break;
+                       blocks[page_block] = map_bh->b_blocknr + map_offset +
+                                               relative_block;
+                       page_block++;
+                       block_in_file++;
+               }
+               bdev = map_bh->b_bdev;
+       }
+
+       /*
+        * Then do more get_blocks calls until we are done with this page.
+        */
+       map_bh->b_page = page;
+       while (page_block < blocks_per_page) {
+               map_bh->b_state = 0;
+               map_bh->b_size = 0;
+
+               if (block_in_file < last_block) {
+                       map_bh->b_size = (last_block-block_in_file) << blkbits;
+                       if (get_block(inode, block_in_file, map_bh, 0))
+                               goto confused;
+                       *first_logical_block = block_in_file;
+               }
+
+               if (!buffer_mapped(map_bh)) {
+                       fully_mapped = 0;
+                       if (first_hole == blocks_per_page)
+                               first_hole = page_block;
+                       page_block++;
+                       block_in_file++;
+                       continue;
+               }
+
+               /* some filesystems will copy data into the page during
+                * the get_block call, in which case we don't want to
+                * read it again.  map_buffer_to_page copies the data
+                * we just collected from get_block into the page's buffers
+                * so readpage doesn't have to repeat the get_block call
+                */
+               if (buffer_uptodate(map_bh)) {
+                       map_buffer_to_page(page, map_bh, page_block);
+                       goto confused;
+               }
+
+               if (first_hole != blocks_per_page)
+                       goto confused;          /* hole -> non-hole */
+
+               /* Contiguous blocks? */
+               if (page_block && blocks[page_block-1] != map_bh->b_blocknr-1)
+                       goto confused;
+               nblocks = map_bh->b_size >> blkbits;
+               for (relative_block = 0; ; relative_block++) {
+                       if (relative_block == nblocks) {
+                               clear_buffer_mapped(map_bh);
+                               break;
+                       } else if (page_block == blocks_per_page)
+                               break;
+                       blocks[page_block] = map_bh->b_blocknr+relative_block;
+                       page_block++;
+                       block_in_file++;
+               }
+               bdev = map_bh->b_bdev;
+       }
+
+       if (first_hole != blocks_per_page) {
+               zero_user_segment(page, first_hole << blkbits, PAGE_CACHE_SIZE);
+               if (first_hole == 0) {
+                       SetPageUptodate(page);
+                       unlock_page(page);
+                       goto out;
+               }
+       } else if (fully_mapped) {
+               SetPageMappedToDisk(page);
+       }
+
+       if (fully_mapped && blocks_per_page == 1 && !PageUptodate(page) &&
+           cleancache_get_page(page) == 0) {
+               SetPageUptodate(page);
+               goto confused;
+       }
+
+       /*
+        * This page will go to BIO.  Do we need to send this BIO off first?
+        */
+       if (bio && (*last_block_in_bio != blocks[0] - 1))
+               bio = mpage_bio_submit(READ, bio);
+
+alloc_new:
+       if (bio == NULL) {
+               if (first_hole == blocks_per_page) {
+                       if (!bdev_read_page(bdev, blocks[0] << (blkbits - 9),
+                                                               page))
+                               goto out;
+               }
+               bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
+                               min_t(int, nr_pages, bio_get_nr_vecs(bdev)),
+                               GFP_KERNEL);
+               if (bio == NULL)
+                       goto confused;
+       }
+
+       length = first_hole << blkbits;
+       if (bio_add_page(bio, page, length, 0) < length) {
+               bio = mpage_bio_submit(READ, bio);
+               goto alloc_new;
+       }
+
+       relative_block = block_in_file - *first_logical_block;
+       nblocks = map_bh->b_size >> blkbits;
+       if ((buffer_boundary(map_bh) && relative_block == nblocks) ||
+           (first_hole != blocks_per_page))
+               bio = mpage_bio_submit(READ, bio);
+       else
+               *last_block_in_bio = blocks[blocks_per_page - 1];
+out:
+       return bio;
+
+confused:
+       if (bio)
+               bio = mpage_bio_submit(READ, bio);
+       if (!PageUptodate(page))
+               block_read_full_page(page, get_block);
+       else
+               unlock_page(page);
+       goto out;
+}
+
+int ext4_readpage(struct file *file, struct page *page)
+{
+       unsigned long           first_logical_block = 0;
+       struct buffer_head      map_bh;
+       struct inode            *inode = page->mapping->host;
+       struct bio              *bio = NULL;
+       sector_t                last_block_in_bio = 0;
+       int                     ret = -EAGAIN;
 
        trace_ext4_readpage(page);
 
        if (ext4_has_inline_data(inode))
                ret = ext4_readpage_inline(inode, page);
 
-       if (ret == -EAGAIN)
-               return mpage_readpage(page, ext4_get_block);
+       if (ret != -EAGAIN)
+               return ret;
 
-       return ret;
+       map_bh.b_state = 0;
+       map_bh.b_size = 0;
+       bio = do_mpage_readpage(bio, page, 1, &last_block_in_bio,
+                       &map_bh, &first_logical_block, ext4_get_block);
+       if (bio)
+               mpage_bio_submit(READ, bio);
+       return 0;
 }
 
 int ext4_readpages(struct file *file, struct address_space *mapping,
                   struct list_head *pages, unsigned nr_pages)
 {
        struct inode *inode = mapping->host;
+       struct bio *bio = NULL;
+       unsigned page_idx;
+       sector_t last_block_in_bio = 0;
+       struct buffer_head map_bh;
+       unsigned long first_logical_block = 0;
 
        /* If the file has inline data, no need to do readpages. */
        if (ext4_has_inline_data(inode))
                return 0;
 
-       return mpage_readpages(mapping, pages, nr_pages, ext4_get_block);
+       map_bh.b_state = 0;
+       map_bh.b_size = 0;
+       for (page_idx = 0; page_idx < nr_pages; page_idx++) {
+               struct page *page = list_entry(pages->prev, struct page, lru);
+
+               prefetchw(&page->flags);
+               list_del(&page->lru);
+               if (!add_to_page_cache_lru(page, mapping,
+                                       page->index, GFP_KERNEL)) {
+                       bio = do_mpage_readpage(bio, page,
+                                       nr_pages - page_idx,
+                                       &last_block_in_bio, &map_bh,
+                                       &first_logical_block,
+                                       ext4_get_block);
+               }
+               page_cache_release(page);
+       }
+       BUG_ON(!list_empty(pages));
+       if (bio)
+               mpage_bio_submit(READ, bio);
+       return 0;
 }