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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 <kernel@teksavvy.com> 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

    Mark,

    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
    wiper.sh 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 wiper.sh, what kernel are you testing
    with?

    Greg
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