> > @@ -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);
> > }
>
> Can the new shift operation overflow? If so, how about using
> check_shl_overflow()?
Actually, overflow might be not heppen in case of physical device.
But I modified as below. feedback about this.
@@ -168,6 +169,9 @@ void blk_queue_max_hw_sectors(struct request_queue *q, unsigned int max_hw_secto
limits->logical_block_size >> SECTOR_SHIFT);
limits->max_sectors = max_sectors;
+ limits->bio_max_bytes = check_shl_overflow(max_sectors, SECTOR_SHIFT,
+ &limits->bio_max_bytes) ? UINT_MAX : max_sectors << SECTOR_SHIFT;
+
q->backing_dev_info->io_pages = max_sectors >> (PAGE_SHIFT - 9);
}
EXPORT_SYMBOL(blk_queue_max_hw_sectors);
>
> >>> @@ -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);
> >>
> >> The above will limit bio_max_bytes for all stacked block devices, which
> >> is something we do not want. I propose to set t->bio_max_bytes to
> >> UINT_MAX in blk_stack_limits() and to let the stacked driver (e.g.
> >> dm-crypt) decide whether or not to lower that value.
> >
> > Actually, bio size should be limited in dm-crypt too. Because almost I/O
> > from user space will be gone to dm-crypt first. I/O issue timing will be
> > delayed if bio size is not limited in dm-crypt.
> > Do you have any idea to decide whether takes lower bio max size, or not
> > in the stacked driver?
> > Add a flag to decide this in driver layer like before?
> > Or insert code manually in each stacked driver if it is needed?
>
> There will be fewer stacked drivers for which the bio size has to be
> limited than for which the bio size has not to be limited. Hence the
> proposal to set t->bio_max_bytes to UINT_MAX in blk_stack_limits() and
> to let the stacked driver (e.g. dm-crypt) decide whether or not to lower
> that value.
I see what you said. I'll set t->bio_max_bytes to UINT_MAX in
blk_stack_limits() as you mentioned.
>
> > 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);
>
> You may want to define bio_max_size() as an inline function in bio.h
> such that no additional function calls are introduced in the hot path.
I tried, but it is not easy. because request_queue structure of blkdev.h
should be referred in bio.h. I think it's not good to apply as a inline function.
Thanks,
Changheun Lee.
