On Mon, Jan 30, 2023 at 01:26:51PM -0800, Bart Van Assche wrote:
> Allow block drivers to configure the following:
> * Maximum number of hardware sectors values smaller than
> PAGE_SIZE >> SECTOR_SHIFT. With PAGE_SIZE = 4096 this means that values
> below 8 are supported.
> * A maximum segment size below the page size. This is most useful
> for page sizes above 4096 bytes.
>
> The blk_sub_page_segments static branch will be used in later patches to
> prevent that performance of block drivers that support segments >=
> PAGE_SIZE and max_hw_sectors >= PAGE_SIZE >> SECTOR_SHIFT would be affected.
This commit log seems to not make it clear if there is a functional
change or not.
> @@ -100,6 +106,55 @@ void blk_queue_bounce_limit(struct request_queue *q, enum blk_bounce bounce)
> }
> EXPORT_SYMBOL(blk_queue_bounce_limit);
>
> +/* For debugfs. */
> +int blk_sub_page_limit_queues_get(void *data, u64 *val)
> +{
> + *val = READ_ONCE(blk_nr_sub_page_limit_queues);
> +
> + return 0;
> +}
> +
> +/**
> + * blk_enable_sub_page_limits - enable support for max_segment_size values smaller than PAGE_SIZE and for max_hw_sectors values below PAGE_SIZE >> SECTOR_SHIFT
That's a really long line for kdoc, can't we just trim it?
And why not update the docs to reflect the change?
> @@ -122,12 +177,17 @@ EXPORT_SYMBOL(blk_queue_bounce_limit);
> void blk_queue_max_hw_sectors(struct request_queue *q, unsigned int max_hw_sectors)
> {
> struct queue_limits *limits = &q->limits;
> + unsigned int min_max_hw_sectors = PAGE_SIZE >> SECTOR_SHIFT;
> unsigned int max_sectors;
>
> - if ((max_hw_sectors << 9) < PAGE_SIZE) {
> - max_hw_sectors = 1 << (PAGE_SHIFT - 9);
> - printk(KERN_INFO "%s: set to minimum %d\n",
> - __func__, max_hw_sectors);
> + if (max_hw_sectors < min_max_hw_sectors) {
> + blk_enable_sub_page_limits(limits);
> + min_max_hw_sectors = 1;
> + }
Up to this part this a non-functional update, and so why not a
separate patch to clarify that.
> +
> + if (max_hw_sectors < min_max_hw_sectors) {
> + max_hw_sectors = min_max_hw_sectors;
> + pr_info("%s: set to minimum %u\n", __func__, max_hw_sectors);
But if I understand correctly here we're now changing
max_hw_sectors from 1 to whatever the driver set on
blk_queue_max_hw_sectors() if its smaller than PAGE_SIZE.
To determine if this is a functional change it begs the
question as to how many block drivers have a max hw sector
smaller than the equivalent PAGE_SIZE and wonder if that
could regress.
> }
>
> max_hw_sectors = round_down(max_hw_sectors,
> @@ -282,10 +342,16 @@ EXPORT_SYMBOL_GPL(blk_queue_max_discard_segments);
> **/
> void blk_queue_max_segment_size(struct request_queue *q, unsigned int max_size)
> {
> - if (max_size < PAGE_SIZE) {
> - max_size = PAGE_SIZE;
> - printk(KERN_INFO "%s: set to minimum %d\n",
> - __func__, max_size);
> + unsigned int min_max_segment_size = PAGE_SIZE;
> +
> + if (max_size < min_max_segment_size) {
> + blk_enable_sub_page_limits(&q->limits);
> + min_max_segment_size = SECTOR_SIZE;
> + }
> +
> + if (max_size < min_max_segment_size) {
> + max_size = min_max_segment_size;
> + pr_info("%s: set to minimum %u\n", __func__, max_size);
And similar thing here.
Luis
