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| Started by | Mike Snitzer <snitzer@redhat.com> |
|---|---|
| First post | 2015-07-14 22:50 +0200 |
| Last post | 2015-07-15 13:50 +0200 |
| Articles | 3 — 3 participants |
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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
| From | Mike Snitzer <snitzer@redhat.com> |
|---|---|
| Date | 2015-07-14 22:50 +0200 |
| Subject | Re: [PATCH 3/3] block: by default, limit maximum discard size to 64MB |
| Message-ID | <pMfjj-2VX-15@gated-at.bofh.it> |
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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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| From | Jens Axboe <axboe@fb.com> |
|---|---|
| Date | 2015-07-14 22:50 +0200 |
| Subject | Re: [PATCH 3/3] block: by default, limit maximum discard size to 64MB |
| Message-ID | <pMfjk-2VX-23@gated-at.bofh.it> |
| In reply to | #1183990 |
On 07/14/2015 02:44 PM, Mike Snitzer wrote: > 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. I'd argue that's most of them... But the testing we did was on NVMe. I can limit it to NVMe, no big deal. > If this goes in I know for sure I'll need to work around it in DM-thinp. In any case, that's a good point, dm/md should not have their own lower restrictions. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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| From | Austin S Hemmelgarn <ahferroin7@gmail.com> |
|---|---|
| Date | 2015-07-15 13:50 +0200 |
| Subject | Re: [PATCH 3/3] block: by default, limit maximum discard size to 64MB |
| Message-ID | <pMtmi-6p4-21@gated-at.bofh.it> |
| In reply to | #1183993 |
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On 2015-07-14 17:48, Jens Axboe wrote: > On 07/14/2015 02:45 PM, Jens Axboe wrote: >> On 07/14/2015 02:44 PM, Mike Snitzer wrote: >>> 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. >> >> I'd argue that's most of them... But the testing we did was on NVMe. I >> can limit it to NVMe, no big deal. > > Oh, and LSI flash too, so not just NVMe. > While I don't have time to test it, I have a feeling that such a limit would help with many of the consumer SSD's out there. Secondarily, once this gets in and discard is fixed for BTRFS, I'll have some performance testing to do WRT dm-thinp.
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