From: Jason Gunthorpe via iommu <iommu@lists.linux-foundation.org>
To: Robin Murphy <robin.murphy@arm.com>
Cc: Kevin Tian <kevin.tian@intel.com>,
Ashok Raj <ashok.raj@intel.com>,
linux-kernel@vger.kernel.org,
Christoph Hellwig <hch@infradead.org>,
iommu@lists.linux-foundation.org,
Joao Martins <joao.m.martins@oracle.com>,
Will Deacon <will@kernel.org>
Subject: Re: [RFC PATCHES 1/2] iommu: Add RCU-protected page free support
Date: Thu, 9 Jun 2022 10:32:34 -0300 [thread overview]
Message-ID: <20220609133234.GA1343366@nvidia.com> (raw)
In-Reply-To: <9a339b42-2993-f7e2-3122-764a486e796f@arm.com>
On Thu, Jun 09, 2022 at 02:19:06PM +0100, Robin Murphy wrote:
> Is there a significant benefit to keeping both paths, or could we get away
> with just always using RCU? Realistically, pagetable pages aren't likely to
> be freed all that frequently, except perhaps at domain teardown, but that
> shouldn't really be performance-critical, and I guess we could stick an RCU
> sync point in iommu_domain_free() if we're really worried about releasing
> larger quantities of pages back to the allocator ASAP?
I think you are right, anything that uses the iommu_iotlb_gather may
as well use RCU too.
IIRC the allocators already know that RCU is often sitting on
freed-memory and have some contigency to flush it out before OOMing,
so nothing special should be needed.
Jason
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WARNING: multiple messages have this Message-ID (diff)
From: Jason Gunthorpe <jgg@nvidia.com>
To: Robin Murphy <robin.murphy@arm.com>
Cc: Lu Baolu <baolu.lu@linux.intel.com>,
Joerg Roedel <joro@8bytes.org>, Kevin Tian <kevin.tian@intel.com>,
Ashok Raj <ashok.raj@intel.com>,
Christoph Hellwig <hch@infradead.org>,
Will Deacon <will@kernel.org>,
Joao Martins <joao.m.martins@oracle.com>,
iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCHES 1/2] iommu: Add RCU-protected page free support
Date: Thu, 9 Jun 2022 10:32:34 -0300 [thread overview]
Message-ID: <20220609133234.GA1343366@nvidia.com> (raw)
In-Reply-To: <9a339b42-2993-f7e2-3122-764a486e796f@arm.com>
On Thu, Jun 09, 2022 at 02:19:06PM +0100, Robin Murphy wrote:
> Is there a significant benefit to keeping both paths, or could we get away
> with just always using RCU? Realistically, pagetable pages aren't likely to
> be freed all that frequently, except perhaps at domain teardown, but that
> shouldn't really be performance-critical, and I guess we could stick an RCU
> sync point in iommu_domain_free() if we're really worried about releasing
> larger quantities of pages back to the allocator ASAP?
I think you are right, anything that uses the iommu_iotlb_gather may
as well use RCU too.
IIRC the allocators already know that RCU is often sitting on
freed-memory and have some contigency to flush it out before OOMing,
so nothing special should be needed.
Jason
next prev parent reply other threads:[~2022-06-09 13:32 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-09 7:08 [RFC PATCHES 1/2] iommu: Add RCU-protected page free support Lu Baolu
2022-06-09 7:08 ` Lu Baolu
2022-06-09 7:08 ` [RFC PATCHES 2/2] iommu: Replace put_pages_list() with iommu_free_pgtbl_pages() Lu Baolu
2022-06-09 7:08 ` Lu Baolu
2022-06-09 12:49 ` [RFC PATCHES 1/2] iommu: Add RCU-protected page free support Jason Gunthorpe via iommu
2022-06-09 12:49 ` Jason Gunthorpe
2022-06-09 13:19 ` Robin Murphy
2022-06-09 13:19 ` Robin Murphy
2022-06-09 13:32 ` Jason Gunthorpe via iommu [this message]
2022-06-09 13:32 ` Jason Gunthorpe
2022-06-10 5:59 ` Baolu Lu
2022-06-10 5:59 ` Baolu Lu
2022-06-10 5:37 ` Baolu Lu
2022-06-10 5:37 ` Baolu Lu
2022-06-15 15:40 ` Jason Gunthorpe via iommu
2022-06-15 15:40 ` Jason Gunthorpe
2022-06-16 2:27 ` Baolu Lu
2022-06-16 2:27 ` Baolu Lu
2022-06-20 4:04 ` Jason Gunthorpe via iommu
2022-06-20 4:04 ` Jason Gunthorpe
2022-06-09 17:06 ` Raj, Ashok
2022-06-09 17:06 ` Raj, Ashok
2022-06-10 6:05 ` Baolu Lu
2022-06-10 6:05 ` Baolu Lu
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