[PATCH V6 01/30] block: simplify bio_check_pages_dirty

Ming Lei
2018-06-09T12:31:00Z

From: Christoph Hellwig <hch@lst.de>

bio_check_pages_dirty currently inviolates the invariant that bv_page of
a bio_vec inside bi_vcnt shouldn't be zero, and that is going to become
really annoying with multpath biovecs. Fortunately there isn't any
all that good reason for it - once we decide to defer freeing the bio
to a workqueue holding onto a few additional pages isn't really an
issue anymore. So just check if there is a clean page that needs
dirtying in the first path, and do a second pass to free them if there
was none, while the cache is still hot.

Also use the chance to micro-optimize bio_dirty_fn a bit by not saving
irq state - we know we are called from a workqueue.

Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
block/bio.c | 56 +++++++++++++++++++++-----------------------------------
1 file changed, 21 insertions(+), 35 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index 5f7563598b1c..3e7d117c3346 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1647,19 +1647,15 @@ static void bio_release_pages(struct bio *bio)
struct bio_vec *bvec;
int i;

- bio_for_each_segment_all(bvec, bio, i) {
- struct page *page = bvec->bv_page;
-
- if (page)
- put_page(page);
- }
+ bio_for_each_segment_all(bvec, bio, i)
+ put_page(bvec->bv_page);
}

/*
* bio_check_pages_dirty() will check that all the BIO's pages are still dirty.
* If they are, then fine. If, however, some pages are clean then they must
* have been written out during the direct-IO read. So we take another ref on
- * the BIO and the offending pages and re-dirty the pages in process context.
+ * the BIO and re-dirty the pages in process context.
*
* It is expected that bio_check_pages_dirty() will wholly own the BIO from
* here on. It will run one put_page() against each page and will run one
@@ -1677,52 +1673,42 @@ static struct bio *bio_dirty_list;
*/
static void bio_dirty_fn(struct work_struct *work)
{
- unsigned long flags;
- struct bio *bio;
+ struct bio *bio, *next;

- spin_lock_irqsave(&bio_dirty_lock, flags);
- bio = bio_dirty_list;
+ spin_lock_irq(&bio_dirty_lock);
+ next = bio_dirty_list;
bio_dirty_list = NULL;
- spin_unlock_irqrestore(&bio_dirty_lock, flags);
+ spin_unlock_irq(&bio_dirty_lock);

- while (bio) {
- struct bio *next = bio->bi_private;
+ while ((bio = next) != NULL) {
+ next = bio->bi_private;

bio_set_pages_dirty(bio);
bio_release_pages(bio);
bio_put(bio);
- bio = next;
}
}

void bio_check_pages_dirty(struct bio *bio)
{
struct bio_vec *bvec;
- int nr_clean_pages = 0;
+ unsigned long flags;
int i;

bio_for_each_segment_all(bvec, bio, i) {
- struct page *page = bvec->bv_page;
-
- if (PageDirty(page) || PageCompound(page)) {
- put_page(page);
- bvec->bv_page = NULL;
- } else {
- nr_clean_pages++;
- }
+ if (!PageDirty(bvec->bv_page) && !PageCompound(bvec->bv_page))
+ goto defer;
}

- if (nr_clean_pages) {
- unsigned long flags;
-
- spin_lock_irqsave(&bio_dirty_lock, flags);
- bio->bi_private = bio_dirty_list;
- bio_dirty_list = bio;
- spin_unlock_irqrestore(&bio_dirty_lock, flags);
- schedule_work(&bio_dirty_work);
- } else {
- bio_put(bio);
- }
+ bio_release_pages(bio);
+ bio_put(bio);
+ return;
+defer:
+ spin_lock_irqsave(&bio_dirty_lock, flags);
+ bio->bi_private = bio_dirty_list;
+ bio_dirty_list = bio;
+ spin_unlock_irqrestore(&bio_dirty_lock, flags);
+ schedule_work(&bio_dirty_work);
}
EXPORT_SYMBOL_GPL(bio_check_pages_dirty);

--
2.9.5