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    SubjectRe: [PATCH 1/2] fs: Do not dispatch FITRIM through separate super_operation
    On Wed, Nov 24, 2010 at 9:48 PM, Mark Lord <> wrote:
    > On 10-11-19 11:30 AM, Ted Ts'o wrote:
    >> On Fri, Nov 19, 2010 at 04:44:33PM +0100, Lukas Czerner wrote:
    >>>> But, oddly, it _is_ the default for mke2fs -t ext4,
    >>>> which really threw me for a loop recently.
    >>>> I though my system had locked up when suddenly everything
    >>>> went dead for a very long time (many minutes) while installing a
    >>>> new system.
    >> Yeah, the assumption was doing a single big discard (which is all
    >> mke2fs is doing) should be fast.  At least on sanely implemented SSD's
    >> (i.e., like the Intel X25-M) it should be, since all that should
    >> require is a flash write to the global mapping table, declaring all of
    >> the blocks as free.
    > But mke2fs probably is NOT doing a "single big discard", because for SATA
    > the
    > TRIM command is limited to 64K sectors per range.. and the in-kernel TRIM
    > code only ever does single ranges..
    > So doing a discard over an entire drive-encompassing partition, say.. 100GB,
    > will require 3000+ individual TRIM commands.  At (say) 200msecs each, that
    > adds up to about ten minutes of execution time.  Or less if the drive is
    > faster than that.
    > Whereas.. grouping them into 64-ranges per trim, could reduce the execution
    > time down to perhaps 1/50th of that, or in the range of 10-20 seconds
    > instead.
    > Cheers


    With recent kernels, this is supposed to work as you describe. ie. 64
    contiguous ranges per trim command.

    If you see a significant speed difference between mke2fs and running on that same filesystem immediately after formatting, then
    their is likely a bug worth chasing.

    Are you seeing an actual speed difference, or just assuming there is
    one? If mke2fs is slower than, what kernel are you testing

    Greg Freemyer
    Head of EDD Tape Extraction and Processing team
    Litigation Triage Solutions Specialist
    CNN/TruTV Aired Forensic Imaging Demo -

    The Norcross Group
    The Intersection of Evidence & Technology
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