Hi,
在 2025/08/18 13:56, Christoph Hellwig 写道:
On Mon, Aug 18, 2025 at 11:40:54AM +0800, Yu Kuai wrote:
Then code will be much complex insdie md code, and we'll have to
reimplement the stack limits logical with the consideration if each rdev
is already a stacked rdev. I really do not like this ...
You don't. You get the stacked value as input and then simply decide
if you want to take it or override it. The easiest way to do the
latter is to just stash it away in a local variable before calling
queue_limits_stack_bdev and then reapplying it afterwards.
And in theroy, we can't handle this case just in md code:
scsi disk -> mdarray -> device mapper/loop/nbd ... -> mdarray
I don't see how the code in this series could handle that either.
.
Please take a look at the first patch, nothing special, the new flag
will be passed to the top device.
diff --git a/block/blk-settings.c b/block/blk-settings.c
index 07874e9b609f..46ee538b2be9 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -782,6 +782,7 @@ int blk_stack_limits(struct queue_limits *t, struct
queue_limits *b,
t->features &= ~BLK_FEAT_POLL;
t->flags |= (b->flags & BLK_FLAG_MISALIGNED);
+ t->flags |= (b->flags & BLK_FLAG_STACK_IO_OPT);
t->max_sectors = min_not_zero(t->max_sectors, b->max_sectors);
t->max_user_sectors = min_not_zero(t->max_user_sectors,
@@ -839,7 +840,10 @@ int blk_stack_limits(struct queue_limits *t, struct
queue_limits *b,
b->physical_block_size);
t->io_min = max(t->io_min, b->io_min);
- t->io_opt = lcm_not_zero(t->io_opt, b->io_opt);
+ if (!t->io_opt || !(t->flags & BLK_FLAG_STACK_IO_OPT) ||
+ (b->flags & BLK_FLAG_STACK_IO_OPT))
+ t->io_opt = lcm_not_zero(t->io_opt, b->io_opt);
+
For the case scsi->mdraid:
t->io_opt is set, the flag is set for t and not for b, hence
lcm_not_zero() is skipped
For the case mdraid->dm/loop/nbd ... -> mdarray:
the flag will be set for both t and b, lcm_not_zero() will not be
skipped.
Thanks,
Kuai
t->dma_alignment = max(t->dma_alignment, b->dma_alignment);
/* Set non-power-of-2 compatible chunk_sectors boundary */
