Hello,

On Tue, Aug 09, 2016 at 10:45:47PM +0800, tom.ty89@gmail.com wrote:

From: Tom Yan <redacted>

Currently block layer limit max_hw_sectors is set to
ATA_MAX_SECTORS_LBA48 (65535), for devices with LBA48 support.

However, block layer limit max_sectors (which is the effective
one; also adjustable, upper-bounded by max_hw_sectors) is set to
BLK_DEF_MAX_SECTORS (currently 2560) by the scsi disk driver,
since libata's SATL does not report an Optimal Transfer Length.

This does not make much sense, especially when the current
BLK_DEF_MAX_SECTORS appears to be unsafe for some ATA devices
(see ATA_HORKAGE_MAX_SEC_1024). Truth is, the current value
appears to be arbitrary anyway. See commit d2be537c3ba3
("block: bump BLK_DEF_MAX_SECTORS to 2560").

Therefore, avoid setting dev->max_sectors when it is strictly
necessary. Leave it as 0 otherwise, so that both block layer
limits will remain as SCSI_DEFAULT_MAX_SECTORS (currently 1024).

These changes feel rather gratuitous.  What's the upside here?

Thanks.

-- 
tejun