Re: [PATCH v7 1/3] bio: limit bio max size

[Changheun Lee]

> On 4/12/21 7:55 PM, Changheun Lee wrote:
> > +unsigned int bio_max_size(struct bio *bio)
> > +{
> > +   struct request_queue *q = bio->bi_bdev->bd_disk->queue;
> > +
> > +   if (blk_queue_limit_bio_size(q))
> > +           return blk_queue_get_max_sectors(q, bio_op(bio))
> > +                   << SECTOR_SHIFT;
> > +
> > +   return UINT_MAX;
> > +}
> 
> This patch adds an if-statement to the hot path and that may have a
> slight negative performance impact. I recommend to follow the approach
> of max_hw_sectors. That means removing QUEUE_FLAG_LIMIT_BIO_SIZE and to
> initialize the maximum bio size to UINT_MAX in blk_set_default_limits().
> 
> Thanks,
> 
> Bart.

I modified as Bart's approach. Thanks for your advice.
It's more simple than before. I think it looks good.
Please, review below. I'll prepare new version base on this.


diff --git a/block/bio.c b/block/bio.c
index 50e579088aca..9e5061ecc317 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -255,6 +255,13 @@ void bio_init(struct bio *bio, struct bio_vec *table,
 }
 EXPORT_SYMBOL(bio_init);
 
+unsigned int bio_max_size(struct bio *bio)
+{
+       struct request_queue *q = bio->bi_bdev->bd_disk->queue;
+
+       return q->limits.bio_max_bytes;
+}
+
 /**
  * bio_reset - reinitialize a bio
  * @bio:       bio to reset
@@ -866,7 +873,7 @@ bool __bio_try_merge_page(struct bio *bio, struct page 
*page,
                struct bio_vec *bv = &bio->bi_io_vec[bio->bi_vcnt - 1];
 
                if (page_is_mergeable(bv, page, len, off, same_page)) {
-                       if (bio->bi_iter.bi_size > UINT_MAX - len) {
+                       if (bio->bi_iter.bi_size > bio_max_size(bio) - len) {
                                *same_page = false;
                                return false;
                        }
diff --git a/block/blk-settings.c b/block/blk-settings.c
index b4aa2f37fab6..b167e8db856b 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -37,6 +37,7 @@ EXPORT_SYMBOL_GPL(blk_queue_rq_timeout);
  */
 void blk_set_default_limits(struct queue_limits *lim)
 {
+       lim->bio_max_bytes = UINT_MAX;
        lim->max_segments = BLK_MAX_SEGMENTS;
        lim->max_discard_segments = 1;
        lim->max_integrity_segments = 0;
@@ -167,6 +168,7 @@ void blk_queue_max_hw_sectors(struct request_queue *q, 
unsigned int max_hw_secto
        max_sectors = round_down(max_sectors,
                                 limits->logical_block_size >> SECTOR_SHIFT);
        limits->max_sectors = max_sectors;
+       limits->bio_max_bytes = max_sectors << SECTOR_SHIFT;
 
        q->backing_dev_info->io_pages = max_sectors >> (PAGE_SHIFT - 9);
 }
@@ -538,6 +540,8 @@ int blk_stack_limits(struct queue_limits *t, struct 
queue_limits *b,
 {
        unsigned int top, bottom, alignment, ret = 0;
 
+       t->bio_max_bytes = min_not_zero(t->bio_max_bytes, b->bio_max_bytes);
+
        t->max_sectors = min_not_zero(t->max_sectors, b->max_sectors);
        t->max_hw_sectors = min_not_zero(t->max_hw_sectors, b->max_hw_sectors);
        t->max_dev_sectors = min_not_zero(t->max_dev_sectors, 
b->max_dev_sectors);
diff --git a/include/linux/bio.h b/include/linux/bio.h
index d0246c92a6e8..e5add63da3af 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -106,6 +106,8 @@ static inline void *bio_data(struct bio *bio)
        return NULL;
 }
 
+extern unsigned int bio_max_size(struct bio *bio);
+
 /**
  * bio_full - check if the bio is full
  * @bio:       bio to check
@@ -119,7 +121,7 @@ static inline bool bio_full(struct bio *bio, unsigned len)
        if (bio->bi_vcnt >= bio->bi_max_vecs)
                return true;
 
-       if (bio->bi_iter.bi_size > UINT_MAX - len)
+       if (bio->bi_iter.bi_size > bio_max_size(bio) - len)
                return true;
 
        return false;
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 158aefae1030..c205d60ac611 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -312,6 +312,8 @@ enum blk_zoned_model {
 };
 
 struct queue_limits {
+       unsigned int            bio_max_bytes;
+
        unsigned long           bounce_pfn;
        unsigned long           seg_boundary_mask;
        unsigned long           virt_boundary_mask;