Re: configurable discard parameters

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>>>>> "Tom" == Tom Yan <tom.ty89@xxxxxxxxx> writes:

Tom> Today I check if blkdiscard really does a full device trim/wipe for
Tom> my Intel 530 SSD (240gb) with hexdump. I end up found that it fail
Tom> to do so because it report garbage info on its block limits VPD.

It is a SATA-attached drive, it has no block limits VPD. What you are
seeing is information prepared by libata's SATL.

Tom> The fact is, in each iteration, for this drive, blkdiscard can only
Tom> trim a maximum of 65528 sectors, which is the largest multiple of 8
Tom> sectors, which is the minimum possible.

  Maximum write same length: 0x3fffc0 blocks

That's 2GB-e per request for a drive with 512-byte logical blocks.

Tom> but still I would like to know why the kernel doesn't allow
Tom> "discard_granularity" and "discard_max_bytes" to be configurable
Tom> for users.

Because if the vendor got these trivial values wrong there is little to
no chance that they implemented discard correctly in their firmware.

-- 
Martin K. Petersen	Oracle Linux Engineering
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