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Re: [PATCH 3/3] block: by default, limit maximum discard size to 64MB

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On Tue, Jul 14 2015 at  2:48pm -0400,
Jens Axboe <axboe@fb.com> wrote:

> Lots of devices exhibit very high latencies for big discards, hurting
> reads and writes. By default, limit the max discard we will build to
> 64MB. This value has shown good results across a number of devices.
> 
> This will potentially hurt discard throughput, from a provisioning
> point of view (when the user does mkfs.xfs, for instance, and mkfs
> issues a full device discard). If that becomes an issue, we could
> have different behavior for provisioning vs runtime discards.
> 
> Signed-off-by: Jens Axboe <axboe@fb.com>

Christoph suggested you impose this default for the specific
drivers/devices that benefit.  I'm not following why imposing a 64MB
default is the right thing to do for all devices.

If this goes in I know for sure I'll need to work around it in DM-thinp.
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Re: [PATCH 3/3] block: by default, limit maximum discard size to 64MB Mike Snitzer <snitzer@redhat.com> - 2015-07-14 22:50 +0200
  Re: [PATCH 3/3] block: by default, limit maximum discard size to  64MB Jens Axboe <axboe@fb.com> - 2015-07-14 22:50 +0200
    Re: [PATCH 3/3] block: by default, limit maximum discard size to  64MB Austin S Hemmelgarn <ahferroin7@gmail.com> - 2015-07-15 13:50 +0200

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