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From: "Morten Brørup" <mb@smartsharesystems.com>
To: "Patrick Robb" <probb@iol.unh.edu>
Cc: "Nicholas Pratte" <npratte@iol.unh.edu>,
	<paul.szczepanek@arm.com>, <juraj.linkes@pantheon.tech>,
	<yoan.picchi@foss.arm.com>, <thomas@monjalon.net>,
	<wathsala.vithanage@arm.com>, <Honnappa.Nagarahalli@arm.com>,
	<dev@dpdk.org>, "Jeremy Spewock" <jspewock@iol.unh.edu>
Subject: RE: [PATCH] dts: Change hugepage runtime config to 2MB Exclusively
Date: Sun, 7 Apr 2024 00:04:24 +0200	[thread overview]
Message-ID: <98CBD80474FA8B44BF855DF32C47DC35E9F376@smartserver.smartshare.dk> (raw)
In-Reply-To: <CAJvnSUA2eV46jkVo_5Utn-wbCGrn_CKujEb8SBR20rN2eQFgsA@mail.gmail.com>

> From: Patrick Robb [mailto:probb@iol.unh.edu]
> Sent: Saturday, 6 April 2024 21.21
> 
> On Sat, Apr 6, 2024 at 4:47 AM Morten Brørup <mb@smartsharesystems.com>
> wrote:
> >
> >
> > This change seems very CPU specific.
> >
> > E.g. in x86 32-bit mode, the hugepage size is 4 MB, not 2 MB.
> >
> > I don't know the recommended hugepage size on other architectures.
> >
> 
> Thanks Morten, that's an important insight which we weren't aware of
> when we initially discussed this ticket.
> 
> We read on some dpdk docs that 1gb hugepages should be set at boot (I
> think the reason is because that's when you can guarantee there is gbs
> of contiguous available memory), and that after boot, only 2gb
> hugepages should be set. I assume that even for other arches which
> don't support the 2mb pages specifically, we still want to allocate
> hugepages using the smallest page size possible per arch (for the same
> reason).

Correct; for very large hugepages, they need to be set at boot.
I don't remember why, but that's the way the Linux kernel works.
2 MB is way below that threshold, and 1 GB is above.

You can also not set nr_overcommit_hugepages for those very large hugepages, only nr_hugepages.

> 
> So I think we can add some dict which stores the smallest valid
> hugepage size per arch. Then during config init, use the config's arch
> value to determine that size, and set the total hugepages allocation
> based on that size and the hugepages count set in the conf.yaml. Or
> maybe we can store the list of all valid hugepgage sizes per arch
> (which are also valid to be set post boot), allow for a new
> hugepage_size value on the conf.yaml, validate the input at config
> init, and then set according to those values. I prefer the former
> option though as I don't think the added flexibility offered by the
> latter seems important.

I agree; the former option suffices.

A tiny detail...
ARM supports multiple (4, I think) different hugepage sizes, where the smallest size is 64 KB.
So you might want to choose another hugepage size than the smallest; but I still agree with your proposed concept of using one specific hugepage size per arch.

Like x86_64, ARM also supports 2 MB and 1 GB hugepage sizes, and 2 MB hugepages is also the typical default on Linux.

I don't know which hugepage sizes are supported by other architectures.
It might only be 32-bit x86 that needs a different hugepage size than 2 MB.


  reply	other threads:[~2024-04-06 22:04 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-04-04 15:31 Nicholas Pratte
2024-04-05 14:27 ` Patrick Robb
2024-04-06  8:47 ` Morten Brørup
2024-04-06 19:20   ` Patrick Robb
2024-04-06 22:04     ` Morten Brørup [this message]
2024-04-08  8:10       ` Bruce Richardson
2024-04-08  9:35         ` Morten Brørup
2024-04-09 16:57           ` Nicholas Pratte
2024-04-09 17:28 ` [PATCH v2] " Nicholas Pratte
2024-04-10  7:23   ` Morten Brørup
2024-04-10 13:50     ` Patrick Robb
2024-04-10 10:43   ` Juraj Linkeš
2024-04-16 18:18 ` [PATCH v3] " Nicholas Pratte
2024-04-16 18:25   ` Morten Brørup
2024-04-16 18:26   ` Nicholas Pratte
2024-04-17 13:46   ` Juraj Linkeš
2024-04-18 16:10 ` [PATCH v4] " Nicholas Pratte
2024-04-25  8:00   ` Juraj Linkeš
2024-04-29 17:26     ` Nicholas Pratte
2024-04-30  8:42       ` Juraj Linkeš

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