John, > Some drive manufacturers export a very large supported max discard > size. However, when the operating system sends I/O of the max size to > the device, extreme I/O latency can often be encountered. Since > hardware does not provide an optimal discard value in addition to the > max, and there is no way to foreshadow how well a drive handles the > large size, take the method from max_sectors setting, and use > BLK_DEF_MAX_SECTORS to set a more reasonable default discard max. This > should avoid the extreme latency while still allowing the user to > increase the value for specific needs. What's reasonable for one device may be completely unreasonable for another. 4 * BLK_DEF_MAX_SECTORS is *tiny* and will penalize performance on many devices. If there's a problem with a device returning something that doesn't make sense, let's quirk it. -- Martin K. Petersen Oracle Linux Engineering
