The atomic write unit max value is limited by any stacked device stripe size.
It is required that the atomic write unit is a power-of-2 factor of the stripe size. Currently we use io_min limit to hold the stripe size, and check for a io_min <= SECTOR_SIZE when deciding if we have a striped stacked device. Nilay reports that this causes a problem when the physical block size is greater than SECTOR_SIZE [0]. Furthermore, io_min may be mutated when stacking devices, and this makes it a poor candidate to hold the stripe size. Such an example (of when io_min may change) would be when the io_min is less than the physical block size. Use chunk_sectors to hold the stripe size, which is more appropriate. [0] https://lore.kernel.org/linux-block/888f3b1d-7817-4007-b3b3-1a2ea04df...@linux.ibm.com/T/#mecca17129f72811137d3c2f1e477634e77f06781 Reviewed-by: Nilay Shroff <ni...@linux.ibm.com> Signed-off-by: John Garry <john.g.ga...@oracle.com> --- block/blk-settings.c | 51 +++++++++++++++++++++++++------------------- 1 file changed, 29 insertions(+), 22 deletions(-) diff --git a/block/blk-settings.c b/block/blk-settings.c index 7ca21fb32598..20d3563f5d3f 100644 --- a/block/blk-settings.c +++ b/block/blk-settings.c @@ -596,41 +596,47 @@ static bool blk_stack_atomic_writes_boundary_head(struct queue_limits *t, return true; } +static inline unsigned int max_pow_of_two_factor(const unsigned int nr) +{ + return 1 << (ffs(nr) - 1); +} -/* Check stacking of first bottom device */ -static bool blk_stack_atomic_writes_head(struct queue_limits *t, - struct queue_limits *b) +static void blk_stack_atomic_writes_chunk_sectors(struct queue_limits *t) { - if (b->atomic_write_hw_boundary && - !blk_stack_atomic_writes_boundary_head(t, b)) - return false; + unsigned int chunk_bytes = t->chunk_sectors << SECTOR_SHIFT; - if (t->io_min <= SECTOR_SIZE) { - /* No chunk sectors, so use bottom device values directly */ - t->atomic_write_hw_unit_max = b->atomic_write_hw_unit_max; - t->atomic_write_hw_unit_min = b->atomic_write_hw_unit_min; - t->atomic_write_hw_max = b->atomic_write_hw_max; - return true; - } + if (!t->chunk_sectors) + return; /* * Find values for limits which work for chunk size. * b->atomic_write_hw_unit_{min, max} may not be aligned with chunk - * size (t->io_min), as chunk size is not restricted to a power-of-2. + * size, as the chunk size is not restricted to a power-of-2. * So we need to find highest power-of-2 which works for the chunk * size. - * As an example scenario, we could have b->unit_max = 16K and - * t->io_min = 24K. For this case, reduce t->unit_max to a value - * aligned with both limits, i.e. 8K in this example. + * As an example scenario, we could have t->unit_max = 16K and + * t->chunk_sectors = 24KB. For this case, reduce t->unit_max to a + * value aligned with both limits, i.e. 8K in this example. */ - t->atomic_write_hw_unit_max = b->atomic_write_hw_unit_max; - while (t->io_min % t->atomic_write_hw_unit_max) - t->atomic_write_hw_unit_max /= 2; + t->atomic_write_hw_unit_max = min(t->atomic_write_hw_unit_max, + max_pow_of_two_factor(chunk_bytes)); - t->atomic_write_hw_unit_min = min(b->atomic_write_hw_unit_min, + t->atomic_write_hw_unit_min = min(t->atomic_write_hw_unit_min, t->atomic_write_hw_unit_max); - t->atomic_write_hw_max = min(b->atomic_write_hw_max, t->io_min); + t->atomic_write_hw_max = min(t->atomic_write_hw_max, chunk_bytes); +} +/* Check stacking of first bottom device */ +static bool blk_stack_atomic_writes_head(struct queue_limits *t, + struct queue_limits *b) +{ + if (b->atomic_write_hw_boundary && + !blk_stack_atomic_writes_boundary_head(t, b)) + return false; + + t->atomic_write_hw_unit_max = b->atomic_write_hw_unit_max; + t->atomic_write_hw_unit_min = b->atomic_write_hw_unit_min; + t->atomic_write_hw_max = b->atomic_write_hw_max; return true; } @@ -658,6 +664,7 @@ static void blk_stack_atomic_writes_limits(struct queue_limits *t, if (!blk_stack_atomic_writes_head(t, b)) goto unsupported; + blk_stack_atomic_writes_chunk_sectors(t); return; unsupported: -- 2.43.5
