Date: Tue, 21 May 2024 13:45:41 +0530
From: Nitesh Shetty <nj.shetty@...sung.com>
To: Damien Le Moal <dlemoal@...nel.org>
Cc: Jens Axboe <axboe@...nel.dk>, Jonathan Corbet <corbet@....net>, Alasdair
	Kergon <agk@...hat.com>, Mike Snitzer <snitzer@...nel.org>, Mikulas Patocka
	<mpatocka@...hat.com>, Keith Busch <kbusch@...nel.org>, Christoph Hellwig
	<hch@....de>, Sagi Grimberg <sagi@...mberg.me>, Chaitanya Kulkarni
	<kch@...dia.com>, Alexander Viro <viro@...iv.linux.org.uk>, Christian
	Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
	martin.petersen@...cle.com, bvanassche@....org, david@...morbit.com,
	hare@...e.de, damien.lemoal@...nsource.wdc.com, anuj20.g@...sung.com,
	joshi.k@...sung.com, nitheshshetty@...il.com, gost.dev@...sung.com,
	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org, dm-devel@...ts.linux.dev,
	linux-nvme@...ts.infradead.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v20 01/12] block: Introduce queue limits and sysfs for
 copy-offload support

On 20/05/24 04:33PM, Damien Le Moal wrote:
>On 2024/05/20 12:20, Nitesh Shetty wrote:
>> @@ -231,10 +237,11 @@ int blk_set_default_limits(struct queue_limits *lim)
>>  {
>>  	/*
>>  	 * Most defaults are set by capping the bounds in blk_validate_limits,
>> -	 * but max_user_discard_sectors is special and needs an explicit
>> -	 * initialization to the max value here.
>> +	 * but max_user_discard_sectors and max_user_copy_sectors are special
>> +	 * and needs an explicit initialization to the max value here.
>
>s/needs/need

acked
>
>>  	 */
>>  	lim->max_user_discard_sectors = UINT_MAX;
>> +	lim->max_user_copy_sectors = UINT_MAX;
>>  	return blk_validate_limits(lim);
>>  }
>>
>> @@ -316,6 +323,25 @@ void blk_queue_max_discard_sectors(struct request_queue *q,
>>  }
>>  EXPORT_SYMBOL(blk_queue_max_discard_sectors);
>>
>> +/*
>> + * blk_queue_max_copy_hw_sectors - set max sectors for a single copy payload
>> + * @q:	the request queue for the device
>> + * @max_copy_sectors: maximum number of sectors to copy
>> + */
>> +void blk_queue_max_copy_hw_sectors(struct request_queue *q,
>> +				   unsigned int max_copy_sectors)
>> +{
>> +	struct queue_limits *lim = &q->limits;
>> +
>> +	if (max_copy_sectors > (BLK_COPY_MAX_BYTES >> SECTOR_SHIFT))
>> +		max_copy_sectors = BLK_COPY_MAX_BYTES >> SECTOR_SHIFT;
>> +
>> +	lim->max_copy_hw_sectors = max_copy_sectors;
>> +	lim->max_copy_sectors =
>> +		min(max_copy_sectors, lim->max_user_copy_sectors);
>> +}
>> +EXPORT_SYMBOL_GPL(blk_queue_max_copy_hw_sectors);
>
>Hmm... Such helper seems to not fit with Christoph's changes of the limits
>initialization as that is not necessarily done using &q->limits but depending on
>the driver, a different limit structure. So shouldn't this function be passed a
>queue_limits struct pointer instead of the request queue pointer ?
>
Acked, we made a mistake, we are no longer using this function after moving
to atomic limits change. We will remove this function in next version.

>> +
>>  /**
>>   * blk_queue_max_secure_erase_sectors - set max sectors for a secure erase
>>   * @q:  the request queue for the device
>> @@ -633,6 +659,10 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
>>  	t->max_segment_size = min_not_zero(t->max_segment_size,
>>  					   b->max_segment_size);
>>
>> +	t->max_copy_sectors = min(t->max_copy_sectors, b->max_copy_sectors);
>> +	t->max_copy_hw_sectors = min(t->max_copy_hw_sectors,
>> +				     b->max_copy_hw_sectors);
>> +
>>  	t->misaligned |= b->misaligned;
>>
>>  	alignment = queue_limit_alignment_offset(b, start);
>> diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
>> index f0f9314ab65c..805c2b6b0393 100644
>> --- a/block/blk-sysfs.c
>> +++ b/block/blk-sysfs.c
>> @@ -205,6 +205,44 @@ static ssize_t queue_discard_zeroes_data_show(struct request_queue *q, char *pag
>>  	return queue_var_show(0, page);
>>  }
>>
>> +static ssize_t queue_copy_hw_max_show(struct request_queue *q, char *page)
>> +{
>> +	return sprintf(page, "%llu\n", (unsigned long long)
>> +		       q->limits.max_copy_hw_sectors << SECTOR_SHIFT);
>> +}
>> +
>> +static ssize_t queue_copy_max_show(struct request_queue *q, char *page)
>> +{
>> +	return sprintf(page, "%llu\n", (unsigned long long)
>> +		       q->limits.max_copy_sectors << SECTOR_SHIFT);
>> +}
>
>Given that you repeat the same pattern twice, may be add a queue_var64_show()
>helper ? (naming can be changed).
>
Acked

>> +
>> +static ssize_t queue_copy_max_store(struct request_queue *q, const char *page,
>> +				    size_t count)
>> +{
>> +	unsigned long max_copy_bytes;
>> +	struct queue_limits lim;
>> +	ssize_t ret;
>> +	int err;
>> +
>> +	ret = queue_var_store(&max_copy_bytes, page, count);
>> +	if (ret < 0)
>> +		return ret;
>> +
>> +	if (max_copy_bytes & (queue_logical_block_size(q) - 1))
>> +		return -EINVAL;
>> +
>> +	blk_mq_freeze_queue(q);
>> +	lim = queue_limits_start_update(q);
>> +	lim.max_user_copy_sectors = max_copy_bytes >> SECTOR_SHIFT;
>
>max_copy_bytes is an unsigned long, so 64 bits on 64-bit arch and
>max_user_copy_sectors is an unsigned int, so 32-bits. There are thus no
>guarantees that this will not overflow. A check is needed.
>
Acked

>> +	err = queue_limits_commit_update(q, &lim);
>> +	blk_mq_unfreeze_queue(q);
>> +
>> +	if (err)
>
>You can reuse ret here. No need for adding the err variable.
Acked

>
>> +		return err;
>> +	return count;
>> +}
>> +
>>  static ssize_t queue_write_same_max_show(struct request_queue *q, char *page)
>>  {
>>  	return queue_var_show(0, page);
>> @@ -505,6 +543,9 @@ QUEUE_RO_ENTRY(queue_nr_zones, "nr_zones");
>>  QUEUE_RO_ENTRY(queue_max_open_zones, "max_open_zones");
>>  QUEUE_RO_ENTRY(queue_max_active_zones, "max_active_zones");
>>
>> +QUEUE_RO_ENTRY(queue_copy_hw_max, "copy_max_hw_bytes");
>> +QUEUE_RW_ENTRY(queue_copy_max, "copy_max_bytes");
>> +
>>  QUEUE_RW_ENTRY(queue_nomerges, "nomerges");
>>  QUEUE_RW_ENTRY(queue_rq_affinity, "rq_affinity");
>>  QUEUE_RW_ENTRY(queue_poll, "io_poll");
>> @@ -618,6 +659,8 @@ static struct attribute *queue_attrs[] = {
>>  	&queue_discard_max_entry.attr,
>>  	&queue_discard_max_hw_entry.attr,
>>  	&queue_discard_zeroes_data_entry.attr,
>> +	&queue_copy_hw_max_entry.attr,
>> +	&queue_copy_max_entry.attr,
>>  	&queue_write_same_max_entry.attr,
>>  	&queue_write_zeroes_max_entry.attr,
>>  	&queue_zone_append_max_entry.attr,
>> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
>> index aefdda9f4ec7..109d9f905c3c 100644
>> --- a/include/linux/blkdev.h
>> +++ b/include/linux/blkdev.h
>> @@ -309,6 +309,10 @@ struct queue_limits {
>>  	unsigned int		discard_alignment;
>>  	unsigned int		zone_write_granularity;
>>
>> +	unsigned int		max_copy_hw_sectors;
>> +	unsigned int		max_copy_sectors;
>> +	unsigned int		max_user_copy_sectors;
>> +
>>  	unsigned short		max_segments;
>>  	unsigned short		max_integrity_segments;
>>  	unsigned short		max_discard_segments;
>> @@ -933,6 +937,8 @@ void blk_queue_max_secure_erase_sectors(struct request_queue *q,
>>  		unsigned int max_sectors);
>>  extern void blk_queue_max_discard_sectors(struct request_queue *q,
>>  		unsigned int max_discard_sectors);
>> +extern void blk_queue_max_copy_hw_sectors(struct request_queue *q,
>> +					  unsigned int max_copy_sectors);
>>  extern void blk_queue_max_write_zeroes_sectors(struct request_queue *q,
>>  		unsigned int max_write_same_sectors);
>>  extern void blk_queue_logical_block_size(struct request_queue *, unsigned int);
>> @@ -1271,6 +1277,14 @@ static inline unsigned int bdev_discard_granularity(struct block_device *bdev)
>>  	return bdev_get_queue(bdev)->limits.discard_granularity;
>>  }
>>
>> +/* maximum copy offload length, this is set to 128MB based on current testing */
>
>Current testing will not be current in a while... So may be simply say
>"arbitrary" or something. Also please capitalize the first letter of the
>comment. So something like:
>
>/* Arbitrary absolute limit of 128 MB for copy offload. */
>
>> +#define BLK_COPY_MAX_BYTES		(1 << 27)
>
>Also, it is not clear from the name if this is a soft limit or a cap on the
>hardware limit... So at least please adjust the comment to say which one it is.
>
Acked, it is a soft limit.

Thank You,
Nitesh Shetty

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