linux-kernel - Re: [RFC v2 0/3] iommu/intel: Free empty page tables on unmaps

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Message-ID: <2daf168e-e2b2-4b19-9b39-d58b358c8cd9@redhat.com>
Date: Fri, 26 Apr 2024 08:42:34 +0200
From: David Hildenbrand <david@...hat.com>
To: Pasha Tatashin <pasha.tatashin@...een.com>, akpm@...ux-foundation.org,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org, rientjes@...gle.com,
 dwmw2@...radead.org, baolu.lu@...ux.intel.com, joro@...tes.org,
 will@...nel.org, robin.murphy@....com, iommu@...ts.linux.dev,
 Matthew Wilcox <willy@...radead.org>
Subject: Re: [RFC v2 0/3] iommu/intel: Free empty page tables on unmaps

On 26.04.24 05:43, Pasha Tatashin wrote:
> Changelog
> ================================================================
> v2: Use mapcount instead of refcount
>      Synchronized with IOMMU Observability changes.
> ================================================================
> 
> This series frees empty page tables on unmaps. It intends to be a
> low overhead feature.
> 
> The read-writer lock is used to synchronize page table, but most of
> time the lock is held is reader. It is held as a writer for short
> period of time when unmapping a page that is bigger than the current
> iova request. For all other cases this lock is read-only.
> 
> page->mapcount is used in order to track number of entries at each page
> table.

I'm wondering if this will conflict with page_type at some point? We're 
already converting other page table users to ptdesc. CCing Willy.

-- 
Cheers,

David / dhildenb