[PATCH v2 7/9] iomap: Convert write_count to write_bytes_pending

[Matthew Wilcox (Oracle)]

Instead of counting bio segments, count the number of bytes submitted.
This insulates us from the block layer's definition of what a 'same page'
is, which is not necessarily clear once THPs are involved.

Signed-off-by: Matthew Wilcox (Oracle) <wi...@infradead.org>
Reviewed-by: Christoph Hellwig <h...@lst.de>
---
 fs/iomap/buffered-io.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 1cf976a8e55c..64a5cb383f30 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -27,7 +27,7 @@
  */
 struct iomap_page {
        atomic_t                read_bytes_pending;
-       atomic_t                write_count;
+       atomic_t                write_bytes_pending;
        spinlock_t              uptodate_lock;
        unsigned long           uptodate[];
 };
@@ -73,7 +73,7 @@ iomap_page_release(struct page *page)
        if (!iop)
                return;
        WARN_ON_ONCE(atomic_read(&iop->read_bytes_pending));
-       WARN_ON_ONCE(atomic_read(&iop->write_count));
+       WARN_ON_ONCE(atomic_read(&iop->write_bytes_pending));
        WARN_ON_ONCE(bitmap_full(iop->uptodate, nr_blocks) !=
                        PageUptodate(page));
        kfree(iop);
@@ -1047,7 +1047,7 @@ EXPORT_SYMBOL_GPL(iomap_page_mkwrite);
 
 static void
 iomap_finish_page_writeback(struct inode *inode, struct page *page,
-               int error)
+               int error, unsigned int len)
 {
        struct iomap_page *iop = to_iomap_page(page);
 
@@ -1057,9 +1057,9 @@ iomap_finish_page_writeback(struct inode *inode, struct 
page *page,
        }
 
        WARN_ON_ONCE(i_blocks_per_page(inode, page) > 1 && !iop);
-       WARN_ON_ONCE(iop && atomic_read(&iop->write_count) <= 0);
+       WARN_ON_ONCE(iop && atomic_read(&iop->write_bytes_pending) <= 0);
 
-       if (!iop || atomic_dec_and_test(&iop->write_count))
+       if (!iop || atomic_sub_and_test(len, &iop->write_bytes_pending))
                end_page_writeback(page);
 }
 
@@ -1093,7 +1093,8 @@ iomap_finish_ioend(struct iomap_ioend *ioend, int error)
 
                /* walk each page on bio, ending page IO on them */
                bio_for_each_segment_all(bv, bio, iter_all)
-                       iomap_finish_page_writeback(inode, bv->bv_page, error);
+                       iomap_finish_page_writeback(inode, bv->bv_page, error,
+                                       bv->bv_len);
                bio_put(bio);
        }
        /* The ioend has been freed by bio_put() */
@@ -1309,8 +1310,8 @@ iomap_add_to_ioend(struct inode *inode, loff_t offset, 
struct page *page,
 
        merged = __bio_try_merge_page(wpc->ioend->io_bio, page, len, poff,
                        &same_page);
-       if (iop && !same_page)
-               atomic_inc(&iop->write_count);
+       if (iop)
+               atomic_add(len, &iop->write_bytes_pending);
 
        if (!merged) {
                if (bio_full(wpc->ioend->io_bio, len)) {
@@ -1353,7 +1354,7 @@ iomap_writepage_map(struct iomap_writepage_ctx *wpc,
        LIST_HEAD(submit_list);
 
        WARN_ON_ONCE(i_blocks_per_page(inode, page) > 1 && !iop);
-       WARN_ON_ONCE(iop && atomic_read(&iop->write_count) != 0);
+       WARN_ON_ONCE(iop && atomic_read(&iop->write_bytes_pending) != 0);
 
        /*
         * Walk through the page to find areas to write back. If we run off the
-- 
2.28.0